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Ardizzone et al 06
Marine Ecology. ISSN 0173-9565
ORIGINAL ARTICLE
Long-term change in the structure of a Posidonia oceanica
landscape and its reference for a monitoring plan
Giandomenico Ardizzone, Andrea Belluscio & Luigi Maiorano
Animal and Human Biology Department, University of Rome ‘‘La Sapienza’’, Rome, Italy
Keywords Abstract On the basis of a detailed cartographic survey carried out by Side
Cartography; central Tyrrhenian Sea; Scan Sonar and a towed underwater video camera during 2005, and from a ser-
Posidonia oceanica; regression; sampling
ies of historical maps (1959, 1980, 1990), an extensive regression of Posidonia
design; towed video camera.
oceanica (L.) Delile beds was evidenced for a vast area of the central Tyrrhenian
Correspondence Sea (Latium coast, Italy). The total loss of P. oceanica surface was assessed
Giandomenico Ardizzone, Dipartimento di through GIS estimate. In 1959, the Posidonia beds extended over 7290 ha, while
`
Biologia Animale e dell’Uomo, Universita di in the 2005 survey they had regressed to 2899 ha, a loss of about 60% of their
`
Roma ‘‘La Sapienza’’, Viale dell’Universita, coverage. Also the seagrass lower limit showed a general depth decrease in
32 - 00185 Roma, Italy. time. Total seagrass coverage loss and lower limit regression were not uniform
E-mail: giandomenico.ardizzone@uniroma1.it
along the whole investigated areas and three main sub-areas have been identi-
Accepted: 25 September, 2006
fied with different degrees of regression somehow related with coastal potential
human-mediated impacts. From different coverage estimates of the present sur-
doi:10.1111/j.1439-0485.2006.00128.x vey and of the previous maps, minimum sampling areas were calculated
through bootstrapping simulation routines from small sampling areas (Land-
scape Units) to reach the nearest estimate of the observed condition in the dif-
ferent periods.
industrial sewage and urban discharge (Bourcier 1989;
Problem
Pergent-Martini & Pergent 1995, 1996; Balestri et al.
Several studies have documented important regression 2004; Boudouresque 2004), trawl fishing (Ardizzone &
trends for many seagrasses along most of the world’s Pelusi 1984; Sanchez-Lizaso et al. 1990; Sanchez-Jerez &
`
coasts (Walker & McCombe 1992; Marba et al. 1996; `
Ramon-Espla 1996; Ardizzone et al. 2000), and fish farms
Short & Wyllie-Echeveria 1996; Hemminga & Duarte (Delgado et al. 1997, 1999; Ruiz et al. 2001) have been
2000; Duarte 2002). Pollution, in its broadest sense of described. In addition, there are marine operations which
man-induced disturbance of the coastal marine environ- have caused negative impacts on seagrass beds such as
ment, is recognized as the main source of perturbation boat anchoring (Garcia-Charton et al. 1993; Francour
with local direct and indirect impacts which may have an et al. 1999) and dredge operations (Guidetti & Fabiano
effect on the seagrass condition far away from the source 2000; Short & Coles 2001; Gambi et al. 2005; Badalamenti
of disturbance (Boudouresque et al. 2006). et al. 2006). Other authors report about natural causes of
Posidonia oceanica, a well studied seagrass in the Medi- `
Posidonia beds regression (Gallegos et al. 1993; Marba &
terranean Sea, is considered a key species because of its Duarte 1994, 1997). On the contrary, other studies do
´ `
vast distribution along the infralittoral bottoms (Peres & not report significant loss of a Posidonia bed in the last
Picard 1964). years in a bay with a variety of human activities (Leriche
Important problems of regression for Posidonia beds et al. 2006).
have been reported and different sources of impact, such Three main factors of disturbance can be identified
´ `
as coastal development (Peres & Picard 1972; Meinesz among different sources of potential environmental modi-
et al. 1991; Pasqualini et al. 1999; Ruiz & Romero 2003), fications:
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 299
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
1 reduction of light penetration in the water column How, then, can we understand which is the trend of a
due to increased primary production, induced by eutro- Posidonia landscape modification at a reasonable macro-
phic load in the coastal waters, and because of suspended scale? The first step is to map the distribution of Posidon-
inorganic sediments; ia beds with a good level of accuracy for relatively large
2 mechanical direct damage from fishing activity such as areas; the second (if available) is to evaluate reliable his-
trawling, dragging and anchoring in the nearby coastal torical maps, and the third is to set up a monitoring sys-
waters, particularly in recreational areas; tem, trying to minimize the costs of these expensive
3 change in the sediment quality of the sea bottom, surveys over large areas through a partial sampling of the
mainly from well sorted fine sand to silt, due to inputs area to be monitored. While the spatial pattern of terrest-
coming from modification and building up of the coast- rial communities has been studied in depth by landscape
line. ecologists (Forman & Gordon 1986; Turner 1989), little
All these sources of disturbance have markedly experience is at the moment available for the marine
increased during the last 50 years because of the rapid environment and particularly for benthic species, which
growth of human settlement along the Mediterranean are especially suitable for this approach (Garrabou et al.
coastline, where the resident population is doubling every 1998; Kendrick et al. 1999). The temporal evolution of
thirty years and the tourist presence every 15 years (UNEP the spatial pattern of seagrass beds seems to be an inter-
1989, 1996). Much information is available on the sources esting subject for the landscape ecology approach and a
of impact and their effect on seagrass meadows, and dif- GIS application in this broad context will prove to be a
ferent studies have described quantitatively the spatial fundamental tool (Lathrop & Bognar 1998; Zharikov
modification of Posidonia beds (Leriche et al. 2004; Bou- et al. 2005). To map P. oceanica beds in the Mediterra-
douresque et al. 2006). Such information could be helpful nean Sea different methods have been used. We only
in evaluating significant trends to be generalized at a land- remember the use of underwater inspections by SCUBA
scape scale for regional assessment (Borum et al. 2004). diving (Gili & Ros 1985; Falconetti & Meinesz 1989; Ball-
International conventions, EU regulations and national esta et al. 2000), aerial photography (Pasqualini et al.
legislation protect Posidonia beds, try to limit any danger- 1998, 2001; De Falco et al. 2000), Side Scan Sonar (SSS)
ous activity (Relini 1999), but an important obstacle to (Meinesz & Laurent 1978; Colantoni et al. 1982; Cinelli
the formulation of conservation policies is the scarcity of et al. 1995; Pasqualini et al. 1998), underwater videogra-
information on the loss rate of seagrass beds due to the phy (Ardizzone 1991; Norris et al. 1997; Bianchi et al.
scarcity of monitoring programmes. Many projects of sea- 2003), and the integration between these methods (Piazzi
grass coverage cartography have been carried out in many et al. 2000; Brown et al. 2002; Montefalcone et al. 2006).
Mediterranean countries and almost all the Posidonia beds In particular, towed underwater videocameras have been
along the coasts of Spain, France and Italy are known, used to map Caulerpa prolifera beds along the French
but few monitoring programmes and estimates of loss coasts (Meinesz et al. 2001) and coral reef in tropical
rates of seagrass are available (Procaccini et al. 2003). waters (Carleton & Done 1995; Miller 1999). A complete
Since 1990, for example, the Italian Ministry of the Envi- review of P. oceanica beds data acquisition and an appli-
ronment has been funding surveys for many millions of cation of the comparison of ancient Posidonia maps are
Euro to know the extension of the Posidonia beds along in Leriche et al. (2004).
all the Italian coasts (Liguria, Tuscany, Latium, Apulia in The aims of this paper were to evaluate the present cov-
the 1989–1991 and, again, 2001–2003, Sicily and Sardinia erage of large P. oceanica beds off the coast of Latium (Tyr-
in the 1999–2002, Campania and Calabria in the 2002– rhenian Sea, Italy), to compare this condition with three
2004), and nowadays the whole national distribution is historical maps dating back over fifty years, and to calcu-
well known (Ministero dell’Ambiente e del Territorio late through bootstrapping simulations the optimal confid-
2003). This information constitutes an important starting ence limits to obtain the percentage of sea bottom to be
point but it cannot give an estimate of the regression rate. assessed (minimum sampling area) to understand the
The actual condition is therefore that few specific research change in relation to known reference conditions.
studies on modification of spatial distribution of Posidon-
ia beds have been carried out.
Study area
The lack of old historical references and the high costs
of new surveys in areas where these data have been collec- This research was funded by the Latium Regional Admin-
ted in recent years prevent any regular vast-area monitor- istration to obtain an updated map of the Posidonia beds
ing programme. Nevertheless, the critical conservation to be utilized as reference data during reclamation activit-
status of the Posidonia beds along the Italian coasts is by ies on the local beaches that will be operative in the com-
now a matter of general concern. ing future (Regione Lazio 2004).
300 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
The study area is located in the central Tyrrhenian Sea, used. The pixel resolution was 0.30 m. The transducer
between Cape Circeo and Sperlonga (southern Latium, was dragged at an average speed of 3 knots. The ship’s
Italy) an area corresponding to a coastline 30-km long position was determined by a differential global position-
between latitude 41°10¢ N and 41°18¢ N and longitude ing system (DGPS-RTK Leica 500, precision 0.50 m). The
013°05¢ E and 013°25¢ E (Fig. 1). SSS data acquisition software (CODA) was real time
interfaced with the DGPS data acquisition software
PDS2000. Sixty navigation lines ran parallel to the coast
Material and Methods
145 m apart, to allow sonograms to overlap. Six-hundred
Field work kilometres of sonar images were obtained along the Cir-
Side Scan Sonar (SSS) was used to detect the boundaries ceo – Sperlonga coast during a survey carried out in April
of Posidonia beds and their general characteristics; direct 2005.
observations by underwater towed video camera (Ardiz- The acquisition software of SSS applies the slant-range
zone 1991) were utilized to estimate the different bottom corrections to the raw data, using navigation and depth
coverage (Posidonia, dead matte, soft or hard bottom), data supplied from the ship computer log. This process-
the position of the margins, and generally to validate the ing eliminates the distortions caused by the slant of the
SSS interpretation. Integration of direct and indirect beam and fluctuations in the speed of the vessel and its
methods was adopted during this survey to produce the sensor. The system generates real-time printing of the
most accurate possible information on the sea bottom data received at a scale of between 1/1000 and 1/2000 and
coverage. simultaneously stores the digital data on the hard disk.
When we talk of ‘dead matte’ we refer to the inter- The resolution of restitution was 2 and 4 pixels, 100 DPI
twined dead rhizomes of Posidonia oceanica, the inter- 8 bits.
stices of which are filled with sediment. When P. oceanica The images obtained (sonograms) indicated the distri-
leaves die the dead matte is visible at the bottom and the bution and boundaries of the different sediment or mea-
rhizome decays very slowly and may persist for years or dow formations which are characterized by different
centuries according to the sedimentary regime. The pres- shades of grey. The sonograms were used to discriminate
ence of dead matte is therefore indicative of the past pres- P. oceanica beds from both rocky and sandy bottoms.
ence of the meadow. Direct observations by the towed vehicle were used to
The SSS used in this study was a Towfish EdgeTech validate the indirect methods and to obtain more detailed
model 272 TD, equipped with a transducer transmitting information about the Posidonia beds. An underwater
an acoustic signal at a frequency varying from 100 to video camera mounted on a sledge-like frame was towed
500 kHz. For the present work, a 100-kHz TVG Range a few metres over the bottom by a supply vessel at low
(100 kHz) signal with a maximum slant range of 75 m speed (max 2 knots). An umbilical cable 100-m long con-
per channel on each side of the tow-fish transducer was nected the camera with the control unit on board. The
towed camera was equipped with a compass and a digital
depth meter. The images transmitted directly to the sur-
face allowed observations in real time. The video observa-
tions were carried out along routes orthogonal to the
coast with a shooting width of around 10 m. The bathy-
metric interval ranged from 4 to 40 m. About 42 km of
sea bottom was inspected by means of this video camera
and 165 waypoints were fixed to validate the SSS sono-
grams. All the video images were recorded through digital
media (DVCam tapes) for all the lab processing work.
The boat, the DGPS and the DGPS data acquisition soft-
ware were the same as those used for the SSS survey.
Historical map
The current distribution of P. oceanica in the study area
was compared with the three historical maps dating back
to the last 50 years: Fusco 1961 (1959 survey), Ardizzone
& Migliuolo 1982 (1980 survey), Diviacco et al. 2001
Fig. 1. The study area off the coast of Latium (Tyrrhenian Sea, Italy). (1990 survey). The first one is a map from the Italian
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 301
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
Merchant Navy made by means of discrete data from eco- phological structures of Posidonia beds in relation to
sounder and dredge observations. The original scale of depth (Balestri et al. 2003). To obtain the minimum
the map is 1:100,000. The second map has been made sampling area of Posidonia bed that needs to be surveyed
starting from the first map, and carried out with an accu- to obtain reliable estimates of the modification, resampled
rate SCUBA diving survey. The third map has been car- simulations were performed through bootstrapping re-
ried out within a survey on P. oceanica beds along the sampling technique (it means that the data zj in the ori-
Latium coasts. The survey was carried out by SSS, Remote ginal sample of size s are randomly resampled with
Operate Vehicle, SCUBA diving and DGPS positioning; replacement (j ¼ 1, …s) (Kleijnen et al. 1998). The simu-
the original scale of the map is 1:10,000. lations were done on three (1959, 1990, 2005) of the four
ArcGIS 9.0 and ArcView 3.2 (ESRI) software were used maps that represent the most diverse conditions, to evalu-
to homogenize and to overlay the different maps. Once ate significant surface values in relation to the Posidonia
the total Posidonia coverage was obtained for the four dif- status. For the bootstrapping simulation, the study area
ferent periods (1959, 1980, 1990 and the present 2005), was divided into 2895 LUs. Each simulation was com-
the percentage decrease in the area occupied over time posed of 2895 steps: during the first step, one LU was
was estimated. selected randomly and the percentage of area of LU occu-
pied by Posidonia was measured. The second step added a
second random LU to the first one and the percentage of
Computer simulation
area occupied by Posidonia was measured as the sum of
The last objective of this work was to try to find a monit- the two LUs. During each of the subsequent steps, the
oring method that is the least expensive and at the same simulation randomly added LUs and measured the per-
time efficient in terms of estimating the area occupied by centage of area occupied by Posidonia. At the final step,
Posidonia. Given a reliable starting point, this monitoring the simulation considered all the 2895 LUs and measured
method would eliminate the need for full coverage sur- the percentage of area occupied by Posidonia in the sum
veys (SSS), and thus allow an easier and cheaper monitor- of all the LUs (i.e. we measured the total area of Posidon-
ing design. Ideally the sampling scheme should provide a ia in the three maps). Each step of the simulation was
reliable measure of the area of Posidonia with the lowest considered as a different sampling scheme. The first step
possible number of samples. Such a sampling scheme simulated a sampling scheme with only one LU, the sec-
would be useful in monitoring the conservation status of ond step a scheme with two LUs, and the last step one
Posidonia beds over time (by monitoring we mean a regu- with 2895 LUs covering the entire study area. For each of
lar activity of control in an area where the distribution of the three maps considered, the simulation was carried out
Posidonia has already been mapped and can be utilized as 50 times, giving a total of 144,750 steps for each map.
reference condition). Moreover, the ability to implement Using the results of the simulations, it was possible to
a low-cost up-to-date distribution in relation to historical build for each step (and for each map) the distribution of
coverage, could allow a valid examination of the coher- percentages. As an example, let us take the 1959 map: the
ence of the long-term conservation trends, and offer the simulation built the distribution of percentage areas occu-
chance for timely action. For this purpose, a GIS simula- pied by Posidonia when a sampling scheme with a single
tion of the sampling effort was carried out, considering LU was considered; the same was true up to 2895 LUs
the information collected by the towed video camera on and for the three maps. In this way, we calculated for
bottom strips as potentially useful sampling units of the each step (i.e. for each sampling scheme) the mean per
Posidonia surface. The aim was to calculate from a mini- cent area occupied by Posidonia and the associated stand-
mum surface coverage (the Landscape Unit) operated by ard deviation. As a reference, we considered reliable all
a towed video camera, the minimum level of information the sampling schemes that gave a standard deviation
that was enough to describe with high accuracy and pre- smaller than 5%, but all the distribution was calculated
cision the status of the beds in the different periods. The and any standard deviation value can be considered. The
complete information on the percentage presence of Posi- simulations were carried out in ArcGIS9 (ESRI) using an
donia was derived from the maps available. AML script.
Considering the characteristics of the data sets collected
using the towed video camera, each sampling unit, here-
Results
after called Landscape Unit (LU), was built as a north–
south oriented 10-m-wide strip (the same as the shooting The present day coverage of Posidonia beds has changed
coverage of the video camera), and limited by the coast- radically compared with the other reference periods
line (to the North) and by the depth of 35 m (to the (Fig. 2). In fact, an estimate of 2899 ha of Posidonia and
South), according to the different functional and mor- 1800 ha of dead matte was calculated for the 2005 survey.
302 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
For these three sub-areas, the trend in the reduction of
Posidonia coverage and the modification of the lower
limit were estimated and different conditions were found
(Fig. 3). In 1959, the lower limit of the Posidonia bed was
c. 35 m in the entire study area (Fusco 1961), but it had
markedly changed 20 years later (Ardizzone & Migliuolo
1982) with a mean value of c. 22–24 m in the most
regressed central area and 25 m east of Terracina. In the
1990 survey, the lower limit showed different conditions:
almost the same depth (c. 30–35 m) off Cape Circeo, 20–
22 m in the central part of the area, and 24–25 m east of
Terracina (Diviacco et al. 2001). In the present survey,
the Circeo area is the least modified one, while in the
central area the lower limit further decreased, reaching a
depth of 18–20 m. In the eastern area the present limit is
at 23–25 m.
The upper limit changed less than the lower one, going
from 14 m in 1959 to 17–18 m in the present study,
without any great diversification in the different sub-
areas. The only important exception is off the harbour of
Circeo. From the first estimate of Posidonia coverage of
7290 ha in 1959, the total area in 1980 had become
5054 ha, and 3581 ha in 1990 down to the present value
of 2899 ha. At the same time, no important increase in
the dead matte has been observed. We do not have any
information on the dead matte area in 1959 and 1980 but
a limited increase was observed in the last 10 years, com-
paring the estimated area of 1663 ha in the 1990 to the
present value of 1800 ha, when most of the regression
had already been observed.
The simulation of the different sampling schemes
showed different values in relation to the status of the
Posidonia meadows. The percentages of Posidonia meas-
ured considering the entire surface of the study area
were 69.39% in 1959, 34.31% in 1990 and 27.72% in
Fig. 2. The Posidonia oceanica meadows in the historical maps 2005. For the 1959 map that represents the best and
(1959: from Fusco 1961; 1980: from Ardizzone & Migliuolo 1982; the most regular condition, the simulation suggested
1990: from Diviacco et al. 2001), and in the 2005 survey (present that a sampling scheme with only nine randomly selec-
paper).
ted LUs provided the minimum possible effort for
obtaining a reliable estimate of the area of Posidonia. In
fact, nine randomly selected LUs gave a mean estimate
Three sub-areas, characterized by different conditions can of 70.05% of Posidonia with a standard deviation of
be identified (Fig. 2). The first sub-area (the westernmost 4.92%. In 1990, the minimum sampling effort required
one) is that off Cape Circeo where Posidonia beds were to estimate the condition of Posidonia was of 18 ran-
the least modified over the years. The second sub-area domly selected LUs, corresponding to a mean percent-
(the central one) is located between Cape Circeo and Ter- age of 34.91% with a standard deviation of 4.98%.
racina; here the Posidonia beds display the most consis- In 2005, 21 randomly selected LUs gave a mean of
tent regression in time. This coast has suffered from 27.42% with a standard deviation of 4.89% (Fig. 4). To
important urban change that influenced both water qual- reduce the standard deviation to a value of roughly 1%,
ity and sediment type. The third sub-area (the eastern- we need 221 LUs for 1959 (mean 69.16, SD 0.99%),
most one), located from Terracina to Sperlonga, showed 340 LUs for the 1990 distribution (mean 34.25, SD
a medium regressive status of the Posidonia beds, mainly 0.99%) and 480 LUs for the 2005 distribution (mean
characterized by the decreasing of their lower limits. 27.73, SD 0.99%).
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 303
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
Fig. 3. Trend of the Posidonia oceanica bed coverage (above) and of lower and upper limits of the Posidonia beds (below) in the 1959, 1980,
1990 and 2005 maps and in the different sub-areas.
The validation of old maps is a main test for their use-
Discussion
fulness (Leriche et al. 2004). The 1990 and the present
The very heterogeneous status of the Posidonia beds maps can be considered fully reliable, in our case the lat-
observed in the 30-km long study area stresses the need ter being implemented by SSS full coverage sonograms,
for large-scale studies to understand the complex level of validated by video camera and located by DGPS. The
modification, which is particularly important in cases of other old maps deriving from the interpolation of discrete
regression. The relatively rapid regression observed here data, are important for the upper and lower limits of
can be summarized in the reduction of the bottom cover- tidily distributed Posidonia.
age by c. 60% since 1959, 19% of which has occurred Contrary to the rapid regressive condition of the mea-
since the last survey dating back to 1990. The total loss of dow, the coverage of dead matte does not appear to be
Posidonia beds amounted to 4391 ha in the last 50 years. proportionally increasing. The reason for this lies in the
The extent of this loss is however different in the three structure of the matte. The low-lying matte of the study
main sub-areas. The zone off Cape Circeo showed a little area suffers from physical impact (trawl fishing) and
reduction of the overall surface and lower limits, probably heavy siltation. The dead matte, somewhat eroded and
because the seagrass meadows are located offshore and somewhat covered up by sediment, tends to disappear
therefore are less influenced by continental inputs. How- and therefore is detectable neither by SSS nor by video
ever, this area is also characterized by the presence of camera. The 1990 maps and present maps can explain
hard bottoms, that prevent damage as a consequence of this condition. These two maps have similar total dead
illegal coastal trawling. The exception is the zone immedi- matte surfaces (1663 and 1800 ha) but with different geo-
ately off the harbour of Circeo. This important coastal graphic position due to the shifting of the dead matte
harbour, realized in the 1960s, markedly modified the strip towards the lower Posidonia limit. This limit is mov-
Posidonia bed creating a big discontinuity in its distribu- ing towards the coastline, the new dead matte is following
tion that can be clearly seen from the first image to the the limit, and the old dead matte is disappearing, being
present condition (Fig. 2). eroded and covered by sediment.
The middle area showed the most dramatic coverage This current critical condition is not the result of cata-
and meadow limits reduction. As stated before, this area strophic pollution but is certainly due to the anthropo-
was subjected in the past years to different human genic modifications very common in almost every
impacts that lead to a heavy coastal erosion and turbidity Mediterranean coastal zone (Boudouresque et al. 2006).
of seawaters. Furthermore, an illegal trawling activity is Rapid growth of the human settlements, building of new
today carried out. Finally the third sub-area, from Terra- harbours and breakwaters, input of nutrient coming from
cina to Sperlonga, displayed a medium condition of mea- the intensive agriculture of the area, and the illegal trawl
dow extension and limits regression (Figs 2 and 4). This fishing still being carried on (Ardizzone et al. 2000), are
area is less subject to erosional phenomena, turbid water, without any doubt the joint causes of the observed regres-
illegal trawling and, more general, to human impacts. sions.
304 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
Mediterranean countries, as well. The general status of
regression reported in many scientific works is mainly
linked to spot information on the amount of dead matte
observed in a present day distribution, thus preventing
any evaluation of the dynamic trend of the meadow cov-
erage. But this problem is not only a Mediterranean one.
As reported by Short & Wyllie-Echeverria (1996) ‘a realis-
tic estimate of present seagrasses loss worldwide is not
possible and the few available quantitative reports are cer-
tainly an underestimate of overall loss’. Australia, the
most important continent as to the number of species of
seagrasses and sea bottom coverage, is reported to be
endangered for some species, which have regressed by
45,000 ha in 11 sites (Walker & McCombe 1992), but is
this an important area in relation to the overall amount
of Australian seagrasses or is it negligible? We cannot
answer this question. A similar question is that of the
90,000 ha loss reported for the worldwide decline (Short
& Wyllie-Echeverria 1996).
The results obtained with the simulations for the three
different maps of the Posidonia beds over time showed
that significant information can be obtained on the status
of a meadow already mapped, with a limited sampling
effort and with high accuracy and precision (SD < 5%)
being yielded in the description of the Posidonia surface.
The sampling effort necessary to reach 1% of the standard
deviation value is very high (respectively 221, 340, 480
LUs) and therefore the objective of low cost monitoring
is lost. With only 9, 18, and 21 LUs, we obtained a good
description of the bottom coverage in 1959, 1990, and
2005, respectively, with a 5% standard deviation value.
Moreover, it is evident that the number of the minimum
LUs samples increased in time, as the more regular is the
Posidonia distribution, as in the case of the oldest map,
the more limited is the sampling effort needed. The sur-
Fig. 4. Average percentage of Posidonia oceanica coverage ±SD face percentage covered by the towed video camera,
obtained from GIS simulation for the 1959, 1990 and 2005 maps. which is useful to describe the whole Posidonia distribu-
tion, amounted therefore to 0.3% of the total area for the
1959 map, 0.6% for that of 1990 and 0.7% for the 2005
Evidence of the connection between coastal modifica- one.
tion and regression of Posidonia can be found also when Modern techniques to produce Posidonia bed carto-
comparing the described Posidonia to the status of the graphy at a vast macro-scale are nowadays very
Posidonia meadows in the Pontine Islands, just off the advanced and include different kinds of surveys (SSS,
study area. None of the above mentioned impact factors video camera or ROV, diving), data analysis and GIS
is present in those islands and the Posidonia coverage of elaboration. Their cost is anyhow still very expensive.
the sea bottom is stable, and certainly has been so in the While an initial important effort to obtain detailed refer-
last 15 years (G.D. Ardizzone 1991, unpublished observa- ence cartography for each Posidonia meadow is under-
tions 2005), and without any sign of modification such as standable, the same effort is not feasible and realistic in
the presence of dead matte. a regular monitoring programme. The evidence of
A good knowledge of the Posidonia distribution but at reduction in survey costs with these limited sampling
the same time little well-documented information on his- surfaces could allow the planning of regular monitoring
torical modification of the meadows is the present general programmes implemented by towed video camera sys-
condition of the Italian coastal areas and that of other tems. The costs of these instruments is relatively low,
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 305
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
their use is very simple, needing small craft and a posi-
Acknowledgements
tioning system by means of GPS or DGPS implemented
by a plotter system. Sampling units orthogonal to the This study has been realized thanks to the financial con-
coast, which are useful to estimate significant portions tributions of Latium Regional Administration.
of seagrass beds, should always be adopted and the need
for a stratified sampling design should be considered in
References
the allocation of the random LUs when different charac-
teristics of the distribution are present. Ardizzone G.D. (1991) Cartografia bentonica con sistemi video
This kind of survey is currently being used to validate controllati a distanza. Oebalia, XVII(Suppl), 421–452.
aerial photographs or SSS sonograms for the correct iden- Ardizzone G.D., Migliuolo A. (1982) Modificazioni di una pra-
tification of unidentified patches. The experience already teria di Posidonia oceanica (L.) Delile del Medio Tirreno sot-
obtained evidenced the potentiality of towed underwater `
toposta ad attivita di pesca a strascico. Naturalista Siciliano,
video surveys to monitor very large and already mapped S. IV VI(Suppl. 3), 509–515.
Posidonia beds with limited and low-cost surveys. Ardizzone G.D., Pelusi P. (1984) Yield and damage evaluation
of bottom trawling on Posidonia meadows. In: Boudou-
resque C.F., Jeudy de Grissac A. Oliver J. (Eds), First Inter-
Summary national Workshop on Posidonia oceanica Beds. GIS
Posidonie Publ., France: 1, 63–72.
During a monitoring work along the Latium coast (Cen-
Ardizzone G.D., Tucci P., Somaschini A., Belluscio A.
tral Tyrrhenian Sea) a detailed cartography of Posidonia
(2000) Is bottom trawling responsible for the regression
oceanica beds was implemented by means of SSS and
of Posidonia oceanica meadows in the Mediterranean Sea?
towed video camera techniques in 2005. This cartography In: Kaiser M.J., Groot de S.J. (Eds), Effects of Fishing on
has been compared with several historical maps dating Non-target Species and Habitats. Blackwell Science, Oxford,
back over the last 50 years (1959, 1980 and 1990). More- UK: 37–46.
over, using bootstrap simulations, we were able to obtain Badalamenti F., Di Carlo G., D’Anna G., Gristina M., Toccaceli
the percentage of sea bottom that should be assessed to M. (2006) Effects of dredging activities on population
understand the change in relation to a reference condi- dynamics of Posidonia oceanica (L.) Delile in the Mediterra-
tion. In 1959, the lower limit of the Posidonia bed was nean sea: the case study of Capo Feto (SW Sicily, Italy).
around 35 m in the entire study area. Only 20 years later Hydrobiologia, 555, 253–261.
the value was around 22–24 m, while in the 1990 survey Balestri E., Cinelli F., Lardicci C. (2003) Spatial variation in
the lower limit was at 20–22 m, and in 2005 it was Posidonia oceanica structural, morphological and dynamic
reduced to 18–20 m depth. The total area of Posidonia features in a northwestern Mediterranean coastal area: a
changed from 7290 ha in 1959 to 5054 ha in 1980, and multi-scale analysis. Marine Ecology Progress Series, 250,
from the 3581 ha in 1990 down to the current value of 51–60.
2899 ha, to a total loss of about 60%. The current critical Balestri E., Benedetti Cecchi L., Lardicci C. (2004) Variability
condition is due to anthropogenic modifications very in patterns of growth and morphology of Posidonia oceanica
common in almost every Mediterranean coastal zone. exposed to urban and industrial wastes: contrasts with two
Computer simulations were made on the three maps reference locations. Journal of Experimental Marine Biology
(1959, 1990, 2005) that represent the most diverse condi- and Ecology, 308, 1–21.
Ballesta L., Pasqualini V., Pergent G., Pergent-Martini C.
tions. Sampling units (Landscape Units, LUs) were set up
(2000) Distribution and dynamics of Posidonia oceanica beds
as a north–south oriented strip 10 m wide, and limited
` ´
along the Alberes coastline. Academie de Sciences/Editions
by the coastline and by the 35 m depth. The results
´
scientifiques et medicales. Life Sciences, 323, 407–414.
obtained with the simulations showed that significant
Bianchi C.N., Ardizzone G.D., Belluscio A., Colantoni P.,
information could be obtained on the status of a mea-
Diviacco G., Morri C., Tunesi L. (2003) La cartografia del
dow already mapped, with a limited sampling effort and benthos. In: Gambi M.C., Dappiano M (Eds), Manuale di
yielding a 95% significant description of the Posidonia metodologie di campionamento e studio del benthos marino
surface. With only 9, 18 and 21 LUs, respectively, we mediterraneo. Biologia Marina Mediterranea, 10(Suppl.),
obtained a good description of the bottom coverage in 367–394.
the three periods 1959, 1990 and 2005. The evidence of Borum J., Duarte C.M., Krause-Jensen D., Greve T.M.
reduction of survey costs with these limited sampling (2004) European Seagrasses: An Introduction to Monitoring
surfaces could allow the planning of regular monitoring and Management. EU Project Monitoring and Managing
programmes implemented by towed video camera sys- of European Seagrasses (M&MS) EVK3-CT-2000-00044:
tems. 95 pp.
306 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
Boudouresque C.F. (2004) Marine biodiversity in the Mediter- Francour P., Ganteaume A., Poulain M. (1999) Effects of boat
ranean: status of species, populations and communities. anchoring in Posidonia oceanica seagrass beds in the Port-
Scientific Report of Port-Cros national Park, 20, 97–146. Cros national Park (north-western Mediterranean Sea).
Boudouresque C.F., Bernard G., Bonhomme P., Charbonnel Aquatic Conservation: Marine and Freshwater Ecosystems, 9,
E., Diviacco G., Meinesz A., Pergent G., Pergent-Martini C., 391–400.
Ruitton S., Tunesi L. (2006), Preservation et conservation des Fusco N. (1961) Carta da Pesca n. 3. Da Capo Circeo a Capo
herbiers a Posidonia oceanica. RAMOGE Pub., France: pp. Miseno. Ministero Marina Mercantile. Direzione Generale
1–202. Pesca Marittima.
´
Bourcier M. (1989) Regression des herbiers a Posidonia ocea- `
Gallegos M., Merino M., Marba N., Duarte C.M. (1993) Bio-
´
nica (L.) Delile a l’Est de Marseille, sous l’action conjuguee mass and dynamics of Thalassia testudinum in the Mexican
des activities humaines et des modifications climatiques. In: Caribbean: elucidating rhizome growth. Marine Ecology Pro-
Boudouresque C.F., Meinesz A., Fresi E., Gravez V. (Eds), gress Series, 95, 85–192.
Second International Workshop on Posidonia oceanica beds 2. Gambi M.C., Dappiano M., Lorenti M., Iacono B., Flagella S.,
GIS Posidonie Publ., France: 287–292. Buia M.C. (2005) ‘‘Chronicle of a death foretold’’ – features
Brown C.J., Cooper K.M., Meadows W.J., Limpenny D.S., Rees of a Posidonia oceanica bed impacted by sand extraction. In:
H.L. (2002) Small scale mapping of sea bed assemblages in ¨
Ozhan E. (Ed), Proceedings of the Seventh International Con-
the eastern English Channel using sonar and remote samp- ference on the Mediterranean Coastal Environment, MED-
ling techniques. Estuarine Coastal and Shelf Science, 54, 263– COAST 05, 25–29 October 2005. Kusadasi, Turkey: 441–450.
278. `
Garcia-Charton J.A., Bayle J.T., Sanchez-Lizaso J.L., Chiesa P.,
Carleton J.H., Done T.J. (1995) Quantitative video sampling of ` ´
Llaurado C., Perez C., Djian H. (1993) Respusta de la pra-
coral reef benthos: large-scale application. Coral Reefs, 14(1), dera de Posidonia oceanica y su ictiofauna asociada al anclaje
35–46. de embarcaciones en el parque Nacional de Port Cros, Fran-
Cinelli F., Pardi G., Papi I., Benedetti Cecchi L. (1995) Mappa- cia. Publication Especial del Instituto Espanol de Oceanografia,
tura delle praterie di Posidonia oceanica (L.) Delile intorno 11, 423–430.
`
alle isole minori dell’Arcipelago Toscano. Atti Societa Tos- Garrabou J., Riera J., Zabala M. (1998) Landscape pattern
cana Scienze Naturali, 102, 93–110. indices applied to Mediterranean subtidal rocky benthic
Colantoni P., Gallignani P., Fresi E., Cinelli F. (1982) Patterns communities. Landscape Ecology, 13, 225–247.
of Posidonia oceanica (L.) Delile beds around the island of Gili J. M., Ros J. (1985) Study and cartography of the benthic
Ischia (Gulf of Naples) and adjacent waters. P.S.Z.N.I: Mar- communities of Medes Islands (NE Spain). P.S.Z.N.I: Mar-
ine Ecology, 3 (1), 53–74. ine Ecology, 6(3), 219–238.
De Falco G., Murru E., Baroli M., Piergallini G., Cancemi G. Guidetti P., Fabiano M. (2000) The use of lepidochronology to
(2000) Photo aerial image processing and sediment analysis assess the impact of terrigenous discharges on the primary
as indicators of environmental impact on Posidonia oceanica leaf production of the Mediterranean seagrass Posidonia
in the Mediterranean. Biologia Marina Mediterranea, 7(2), oceanica. Marine Pollution Bulletin, 40, 449–453.
349–352. Hemminga M.A., Duarte C. (2000) Seagrass ecology. Cam-
Delgado O., Grau A., Pou S., Riera F., Massuti C., Zabala M., bridge University Press, Cambridge: 298 pp.
Ballesteros E. (1997) Seagrass regression caused by fish cul- Kendrick G.A., Eckersley J., Walker D.I. (1999) Landscape-
tures in Fornells Bay (Menorca, Western Mediterranean). scale changes in seagrass distribution over time: a case study
Oceanologica Acta, 20, 557–563. from Success Bank, Western Australia. Aquatic Botany, 65,
´
Delgado O., Ruiz J.M., Perez M., Romero J., Ballesteros E. 293–309.
(1999) Effects of fish farming on seagrass (Posidonia oceanic- Kleijnen J.P.C., Feelders A.J., Cheng R.C.H. (1998) Bootstrap-
a) in a Mediterranean bay: seagrass decline after organic ping and validation of metamodels in simulation. In: Medei-
loading cessation. Oceanologica Acta, 22(1), 109–117. ros D.J., Watson E.F., Carson J.S., Manivannan M.S. (Eds),
Diviacco G., Spada E., Virno Lamberti C. (2001) Le Fanero- Proceedings of the 1998 Winter Simulation Conference,
game marine del Lazio. Descrizione e cartografia delle praterie December 13–16, 1998, Washington, DC, USA. 701–706.
di Posidonia oceanica e dei prati di Cymodocea nodosa. Lathrop R.G. Jr, Bognar J.A. (1998) Applying GIS and
Quaderno ICRAM, Roma: 113 pp. landscape ecological principles to evaluate land conserva-
Duarte C.M. (2002) The future of seagrass meadows. Environ- tion alternatives. Landscape and Urban Planning, 41,
mental Conservation, 29, 192–206. 27–41.r.
Falconetti C., Meinesz A. (1989) Charting the seaward limit of Leriche A., Boudouresque C.F., Bernard G., Bonhomme P.,
Posidonia oceanica meadows and of circalittoral biocoenoses Denis J. (2004) A one-century suite of seagrass bed maps:
along the coast of Monaco. Oceanologica Acta, 12 (4), 443– can we trust ancient maps? Estuarine Coastal and Shelf
447. Science, 59, 353–362.
Forman R.T.T., Gordon M. (1986) Landscape Ecology. Wiley, Leriche A., Pasqualini V., Boudouresque C.F., Bernard G.,
New York: 619 pp. Bonhomme P., Clabaut P., Denis J. (2006) Spatial, temporal
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 307
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
and structural variations of a Posidonia oceanica seagrass photogrammetry, and GIS techologies in seagrass mapping.
meadow facing human activities. Aquatic Botany, 84, 287– Photogrammetric Engineering & Remote Sensing, 67, 99–105.
293. Pasqualini V., Pergent-Martini C., Pergent G. (1999) Environ-
`
Marba N., Duarte C.M. (1994) Growth response of the sea- mental impact identification along the Corsican coast
grass Cymodocea nodosa to experimental burial and erosion. (Mediterranean Sea) using image processing. Aquatic Botany,
Marine Ecology Progress Series, 107, 307–311. 65, 311–320.
`
Marba N., Duarte C.M. (1997) Interannual changes in seagrass ´ `
Peres J.M., Picard J. (1964) Nouveau manuel de bionomie
(Posidonia oceanica) growth and environmental changes in ´ ´
benthique de la Mer Mediterranee. Recueil des Travaux de la
the Mediterranean littoral zone. Limnology and Oceanogra- Station Marine d’Endoume, 31, 1–137.
phy, 42, 800–810. ´ ` ´
Peres J.M., Picard J. (1972) Causes de la rarefaction et de
`
Marba N., Duarte C.N., Cebrian J., Enriquez S., Gallegos E., la disparition des herbiers de Posidonia oceanica sur les
Olesen B., Sand-Jensen K. (1996) Growth and population ´ ´
cotes francaises de la Mediterranee. Aquatic Botany, 1,
dynamics of Posidonia oceanica on the Spanish Mediterra- 133–139.
nean coast: elucidating seagrass decline. Marine Ecology Pergent-Martini C., Pergent G. (1995) Impact of a Sewage
Progress Series, 137, 203–213. Treatment Plant on the Posidonia oceanica meadow: assess-
´
Meinesz A., Laurent R. (1978) Cartographie et etat de la limite ment criteria. Proceedings of the Second International Confer-
´
inferiore de l’herbier de Posidonia oceanica dans les Alpes- ence on the Mediterranean Coastal Environment MEDCOAST
maritimes (France). Campagne Poseidon 1976. Botanica ‘95: 1389–1399.
Marina, 21 (8), 513–526.e Pergent-Martini C., Pergent G. (1996) Spatio-temporal dynam-
Meinesz A., Belsher T., Thibaut T., Antolic B., Ben Mustapha ics of Posidonia oceanica beds near a sewage outfall (Medi-
K., Boudouresque C.-F., Chiaverini D., Cinelli F., Cottalorda terranean – France). In: Kuo J., Phillips R.C., Walker D.I.,
J.M., El Abed A., Orestano C., Grau A.M., Ivesa L., Jaklin A., Kirkman H. (Eds), Seagrass Biology: Proceedings of an inter-
Langar R.H., Massuti-Pascual E., Peiraino A., Tunesi L., national workshop. Faculty of Sciences, University of Western
De Vaugelas J., Zavodnik N., Zuliejevic A. (2001) The intro- Australia, Australia: 229–306.
duced green alga Caulerpa taxifolia continues to spread in the Piazzi L., Acunto S., Cinelli F. (2000) Mapping of Posidonia
Mediterranean. Biological Invasion, 3, 201–210. oceanica beds around Elba Island (western Mediterranean)
`
Meinesz A., Lefevre J.R., Astier J.M. (1991) Impact of coastal with integration of direct and indirect methods. Oceanolog-
development on the infralittoral zone along the southern ica Acta, 23 (3), 339–346.
Mediterranean shore of continental France. Marine Pollution Procaccini G., Buia M.C., Gambi M.C., Perez M., Pergent G.,
Bulletin, 23, 343–347. Pergent-Martini C., Romero J. (2003) The Seagrass of the
Millier I.R., Muller R. (1999) Validity and reproducibility of Western Mediterranean. In: Green E.P., Short F.T. (Eds),
benthic cover estimates made during broadscale surveys of World Atlas of Seagrasses. University of California Press,
coral reefs by mantra tow. Coral Reef, 18, 353–356. Berkeley, CA, USA, 48–58.
Ministero dell’Ambiente e del Territorio (2003) Completamento Regione Lazio (2004) Il Progetto BeachMed: Recupero ambi-
delle conoscenze naturalistiche di base. Descrizione di base in entale e mantenimento dei litorali in erosione con l’utilizzo
scala 1:250,000 delle biocenosi marine costiere. Ministero di depositi sabbiosi marini. 3° Quaderno Tecnico, Fase C.
dell’Ambiente. Servizio Conservazione della Natura, ConS- Convenzione 2002-01-4.3-I-028. Regione Lazio Direzione
CN250. `
Generale Ambiente e Protezione Civile – Comunita Europea:
Montefalcone M., Albertelli G., Bianchi C.N., Mariani M., 275 pp.
Morri C. (2006) A new synthetic index and a protocol for Relini G. (1999) L’Italia e la protezione della biodiversita`
monitoring the status of Posidonia oceanica meadows: a in Mediterraneo. Biologia Marina Mediterranea, 6 (1),
case study at Sanremo (Ligurian Sea, NW Mediterranean). 151–171.
Aquatic Conservation: Marine & Freshwater Ecosystems, 16, Ruiz J.M., Romero J. (2003) Effects of disturbances caused by
29–42. coastal constructions on spatial structure, growth dynamics
Norris J.G., Wyllie-Echeverria S., Mumford T., Bailey A., and photosynthesis of the seagrass Posidonia oceanica.
Turner T. (1997) Estimating basal area coverage of subtidal Marine Pollution Bulletin, 46, 1523–1533.
seagrass beds using underwater videography. Aquatic Botany, ´
Ruiz J.M., Peres M., Romero J. (2001) Effect of fish farm loa-
58(3–4), 269–287. dings on seagrass (Posidonia oceanica) distribution, growth
Pasqualini V., Pergent Martini C., Clabaut P., Pergent G and photosynthesis. Marine Pollution Bulletin, 42(9), 749–
(1998) Mapping of Posidonia oceanica using aerial photo- 760.
graphs and side scan sonar: application off the Island of `
Sanchez-Jerez B., Ramon-Espla A.A. (1996) Detection of envi-
Corsica (France). Estuarine Coastal and Shelf Science, 47, ronmental impacts by bottom trawling on Posidonia
359–367. oceanica (L.) Delile meadows: sensitivity of fish and macro-
Pasqualini V., Pergent-Martini C., Clabaut P., Marteel E., benthic communities. Journal of Aquatic Ecosystem Health, 5,
Pergent G. (2001) Integration of aerial remote sensing, 239–253.
308 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
´
Sanchez-Lizaso J.L., Guillen J.E., Ramos A. (1990) The regres- UNEP (1989) State of the Mediterranean marine environment.
sion of Posidonia oceanica meadows in El Campello (Spain). Athens, Greece. MAP Technical Report Series, 28, 48 pp.
´ ´
Rapports et Proces-Verbaux des Reunions de la Commission UNEP (1996) Etat du milieu marin et littoral de la Region
´
internationale pour l’Exploration scientifique de la Mediterra- ´ ´
mediterraneenne. UNEP. MAP Technical Report, 101, 1–148.
`
nee, 32, 7. Walker D.I., McCombe A.J. (1992) Seagrass degradation in
Short F.T., Coles R.G. (2001) Global Seagrass Research Meth- Australian coastal waters. Marine Pollution Bulletin, 25,
ods. Elsevier Science Publishers B.V., Amsterdam, 482 pp. 191–195.
Short F., Wyllie-Echeverria S. (1996) Natural and human Zharikov Y., Skilleter G.A., Loneragan N.R., Taranto T.,
induced disturbance of seagrasses. Environmental Conserva- Bronwyn E.C. (2005) Mapping and characterising
tion, 23 (1), 17–27 subtropical estuarine landscapes using aerial photogra-
Turner M.G. (1989) Landscape ecology: the effect of pattern phy and GIS for potential application in wildlife conserva-
on process. Annual Review of Ecology and Systematics, 20, tion and management. Biological Conservation, 125, 87–
171–197. 100.
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 309
ORIGINAL ARTICLE
Long-term change in the structure of a Posidonia oceanica
landscape and its reference for a monitoring plan
Giandomenico Ardizzone, Andrea Belluscio & Luigi Maiorano
Animal and Human Biology Department, University of Rome ‘‘La Sapienza’’, Rome, Italy
Keywords Abstract On the basis of a detailed cartographic survey carried out by Side
Cartography; central Tyrrhenian Sea; Scan Sonar and a towed underwater video camera during 2005, and from a ser-
Posidonia oceanica; regression; sampling
ies of historical maps (1959, 1980, 1990), an extensive regression of Posidonia
design; towed video camera.
oceanica (L.) Delile beds was evidenced for a vast area of the central Tyrrhenian
Correspondence Sea (Latium coast, Italy). The total loss of P. oceanica surface was assessed
Giandomenico Ardizzone, Dipartimento di through GIS estimate. In 1959, the Posidonia beds extended over 7290 ha, while
`
Biologia Animale e dell’Uomo, Universita di in the 2005 survey they had regressed to 2899 ha, a loss of about 60% of their
`
Roma ‘‘La Sapienza’’, Viale dell’Universita, coverage. Also the seagrass lower limit showed a general depth decrease in
32 - 00185 Roma, Italy. time. Total seagrass coverage loss and lower limit regression were not uniform
E-mail: giandomenico.ardizzone@uniroma1.it
along the whole investigated areas and three main sub-areas have been identi-
Accepted: 25 September, 2006
fied with different degrees of regression somehow related with coastal potential
human-mediated impacts. From different coverage estimates of the present sur-
doi:10.1111/j.1439-0485.2006.00128.x vey and of the previous maps, minimum sampling areas were calculated
through bootstrapping simulation routines from small sampling areas (Land-
scape Units) to reach the nearest estimate of the observed condition in the dif-
ferent periods.
industrial sewage and urban discharge (Bourcier 1989;
Problem
Pergent-Martini & Pergent 1995, 1996; Balestri et al.
Several studies have documented important regression 2004; Boudouresque 2004), trawl fishing (Ardizzone &
trends for many seagrasses along most of the world’s Pelusi 1984; Sanchez-Lizaso et al. 1990; Sanchez-Jerez &
`
coasts (Walker & McCombe 1992; Marba et al. 1996; `
Ramon-Espla 1996; Ardizzone et al. 2000), and fish farms
Short & Wyllie-Echeveria 1996; Hemminga & Duarte (Delgado et al. 1997, 1999; Ruiz et al. 2001) have been
2000; Duarte 2002). Pollution, in its broadest sense of described. In addition, there are marine operations which
man-induced disturbance of the coastal marine environ- have caused negative impacts on seagrass beds such as
ment, is recognized as the main source of perturbation boat anchoring (Garcia-Charton et al. 1993; Francour
with local direct and indirect impacts which may have an et al. 1999) and dredge operations (Guidetti & Fabiano
effect on the seagrass condition far away from the source 2000; Short & Coles 2001; Gambi et al. 2005; Badalamenti
of disturbance (Boudouresque et al. 2006). et al. 2006). Other authors report about natural causes of
Posidonia oceanica, a well studied seagrass in the Medi- `
Posidonia beds regression (Gallegos et al. 1993; Marba &
terranean Sea, is considered a key species because of its Duarte 1994, 1997). On the contrary, other studies do
´ `
vast distribution along the infralittoral bottoms (Peres & not report significant loss of a Posidonia bed in the last
Picard 1964). years in a bay with a variety of human activities (Leriche
Important problems of regression for Posidonia beds et al. 2006).
have been reported and different sources of impact, such Three main factors of disturbance can be identified
´ `
as coastal development (Peres & Picard 1972; Meinesz among different sources of potential environmental modi-
et al. 1991; Pasqualini et al. 1999; Ruiz & Romero 2003), fications:
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 299
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
1 reduction of light penetration in the water column How, then, can we understand which is the trend of a
due to increased primary production, induced by eutro- Posidonia landscape modification at a reasonable macro-
phic load in the coastal waters, and because of suspended scale? The first step is to map the distribution of Posidon-
inorganic sediments; ia beds with a good level of accuracy for relatively large
2 mechanical direct damage from fishing activity such as areas; the second (if available) is to evaluate reliable his-
trawling, dragging and anchoring in the nearby coastal torical maps, and the third is to set up a monitoring sys-
waters, particularly in recreational areas; tem, trying to minimize the costs of these expensive
3 change in the sediment quality of the sea bottom, surveys over large areas through a partial sampling of the
mainly from well sorted fine sand to silt, due to inputs area to be monitored. While the spatial pattern of terrest-
coming from modification and building up of the coast- rial communities has been studied in depth by landscape
line. ecologists (Forman & Gordon 1986; Turner 1989), little
All these sources of disturbance have markedly experience is at the moment available for the marine
increased during the last 50 years because of the rapid environment and particularly for benthic species, which
growth of human settlement along the Mediterranean are especially suitable for this approach (Garrabou et al.
coastline, where the resident population is doubling every 1998; Kendrick et al. 1999). The temporal evolution of
thirty years and the tourist presence every 15 years (UNEP the spatial pattern of seagrass beds seems to be an inter-
1989, 1996). Much information is available on the sources esting subject for the landscape ecology approach and a
of impact and their effect on seagrass meadows, and dif- GIS application in this broad context will prove to be a
ferent studies have described quantitatively the spatial fundamental tool (Lathrop & Bognar 1998; Zharikov
modification of Posidonia beds (Leriche et al. 2004; Bou- et al. 2005). To map P. oceanica beds in the Mediterra-
douresque et al. 2006). Such information could be helpful nean Sea different methods have been used. We only
in evaluating significant trends to be generalized at a land- remember the use of underwater inspections by SCUBA
scape scale for regional assessment (Borum et al. 2004). diving (Gili & Ros 1985; Falconetti & Meinesz 1989; Ball-
International conventions, EU regulations and national esta et al. 2000), aerial photography (Pasqualini et al.
legislation protect Posidonia beds, try to limit any danger- 1998, 2001; De Falco et al. 2000), Side Scan Sonar (SSS)
ous activity (Relini 1999), but an important obstacle to (Meinesz & Laurent 1978; Colantoni et al. 1982; Cinelli
the formulation of conservation policies is the scarcity of et al. 1995; Pasqualini et al. 1998), underwater videogra-
information on the loss rate of seagrass beds due to the phy (Ardizzone 1991; Norris et al. 1997; Bianchi et al.
scarcity of monitoring programmes. Many projects of sea- 2003), and the integration between these methods (Piazzi
grass coverage cartography have been carried out in many et al. 2000; Brown et al. 2002; Montefalcone et al. 2006).
Mediterranean countries and almost all the Posidonia beds In particular, towed underwater videocameras have been
along the coasts of Spain, France and Italy are known, used to map Caulerpa prolifera beds along the French
but few monitoring programmes and estimates of loss coasts (Meinesz et al. 2001) and coral reef in tropical
rates of seagrass are available (Procaccini et al. 2003). waters (Carleton & Done 1995; Miller 1999). A complete
Since 1990, for example, the Italian Ministry of the Envi- review of P. oceanica beds data acquisition and an appli-
ronment has been funding surveys for many millions of cation of the comparison of ancient Posidonia maps are
Euro to know the extension of the Posidonia beds along in Leriche et al. (2004).
all the Italian coasts (Liguria, Tuscany, Latium, Apulia in The aims of this paper were to evaluate the present cov-
the 1989–1991 and, again, 2001–2003, Sicily and Sardinia erage of large P. oceanica beds off the coast of Latium (Tyr-
in the 1999–2002, Campania and Calabria in the 2002– rhenian Sea, Italy), to compare this condition with three
2004), and nowadays the whole national distribution is historical maps dating back over fifty years, and to calcu-
well known (Ministero dell’Ambiente e del Territorio late through bootstrapping simulations the optimal confid-
2003). This information constitutes an important starting ence limits to obtain the percentage of sea bottom to be
point but it cannot give an estimate of the regression rate. assessed (minimum sampling area) to understand the
The actual condition is therefore that few specific research change in relation to known reference conditions.
studies on modification of spatial distribution of Posidon-
ia beds have been carried out.
Study area
The lack of old historical references and the high costs
of new surveys in areas where these data have been collec- This research was funded by the Latium Regional Admin-
ted in recent years prevent any regular vast-area monitor- istration to obtain an updated map of the Posidonia beds
ing programme. Nevertheless, the critical conservation to be utilized as reference data during reclamation activit-
status of the Posidonia beds along the Italian coasts is by ies on the local beaches that will be operative in the com-
now a matter of general concern. ing future (Regione Lazio 2004).
300 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
The study area is located in the central Tyrrhenian Sea, used. The pixel resolution was 0.30 m. The transducer
between Cape Circeo and Sperlonga (southern Latium, was dragged at an average speed of 3 knots. The ship’s
Italy) an area corresponding to a coastline 30-km long position was determined by a differential global position-
between latitude 41°10¢ N and 41°18¢ N and longitude ing system (DGPS-RTK Leica 500, precision 0.50 m). The
013°05¢ E and 013°25¢ E (Fig. 1). SSS data acquisition software (CODA) was real time
interfaced with the DGPS data acquisition software
PDS2000. Sixty navigation lines ran parallel to the coast
Material and Methods
145 m apart, to allow sonograms to overlap. Six-hundred
Field work kilometres of sonar images were obtained along the Cir-
Side Scan Sonar (SSS) was used to detect the boundaries ceo – Sperlonga coast during a survey carried out in April
of Posidonia beds and their general characteristics; direct 2005.
observations by underwater towed video camera (Ardiz- The acquisition software of SSS applies the slant-range
zone 1991) were utilized to estimate the different bottom corrections to the raw data, using navigation and depth
coverage (Posidonia, dead matte, soft or hard bottom), data supplied from the ship computer log. This process-
the position of the margins, and generally to validate the ing eliminates the distortions caused by the slant of the
SSS interpretation. Integration of direct and indirect beam and fluctuations in the speed of the vessel and its
methods was adopted during this survey to produce the sensor. The system generates real-time printing of the
most accurate possible information on the sea bottom data received at a scale of between 1/1000 and 1/2000 and
coverage. simultaneously stores the digital data on the hard disk.
When we talk of ‘dead matte’ we refer to the inter- The resolution of restitution was 2 and 4 pixels, 100 DPI
twined dead rhizomes of Posidonia oceanica, the inter- 8 bits.
stices of which are filled with sediment. When P. oceanica The images obtained (sonograms) indicated the distri-
leaves die the dead matte is visible at the bottom and the bution and boundaries of the different sediment or mea-
rhizome decays very slowly and may persist for years or dow formations which are characterized by different
centuries according to the sedimentary regime. The pres- shades of grey. The sonograms were used to discriminate
ence of dead matte is therefore indicative of the past pres- P. oceanica beds from both rocky and sandy bottoms.
ence of the meadow. Direct observations by the towed vehicle were used to
The SSS used in this study was a Towfish EdgeTech validate the indirect methods and to obtain more detailed
model 272 TD, equipped with a transducer transmitting information about the Posidonia beds. An underwater
an acoustic signal at a frequency varying from 100 to video camera mounted on a sledge-like frame was towed
500 kHz. For the present work, a 100-kHz TVG Range a few metres over the bottom by a supply vessel at low
(100 kHz) signal with a maximum slant range of 75 m speed (max 2 knots). An umbilical cable 100-m long con-
per channel on each side of the tow-fish transducer was nected the camera with the control unit on board. The
towed camera was equipped with a compass and a digital
depth meter. The images transmitted directly to the sur-
face allowed observations in real time. The video observa-
tions were carried out along routes orthogonal to the
coast with a shooting width of around 10 m. The bathy-
metric interval ranged from 4 to 40 m. About 42 km of
sea bottom was inspected by means of this video camera
and 165 waypoints were fixed to validate the SSS sono-
grams. All the video images were recorded through digital
media (DVCam tapes) for all the lab processing work.
The boat, the DGPS and the DGPS data acquisition soft-
ware were the same as those used for the SSS survey.
Historical map
The current distribution of P. oceanica in the study area
was compared with the three historical maps dating back
to the last 50 years: Fusco 1961 (1959 survey), Ardizzone
& Migliuolo 1982 (1980 survey), Diviacco et al. 2001
Fig. 1. The study area off the coast of Latium (Tyrrhenian Sea, Italy). (1990 survey). The first one is a map from the Italian
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 301
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
Merchant Navy made by means of discrete data from eco- phological structures of Posidonia beds in relation to
sounder and dredge observations. The original scale of depth (Balestri et al. 2003). To obtain the minimum
the map is 1:100,000. The second map has been made sampling area of Posidonia bed that needs to be surveyed
starting from the first map, and carried out with an accu- to obtain reliable estimates of the modification, resampled
rate SCUBA diving survey. The third map has been car- simulations were performed through bootstrapping re-
ried out within a survey on P. oceanica beds along the sampling technique (it means that the data zj in the ori-
Latium coasts. The survey was carried out by SSS, Remote ginal sample of size s are randomly resampled with
Operate Vehicle, SCUBA diving and DGPS positioning; replacement (j ¼ 1, …s) (Kleijnen et al. 1998). The simu-
the original scale of the map is 1:10,000. lations were done on three (1959, 1990, 2005) of the four
ArcGIS 9.0 and ArcView 3.2 (ESRI) software were used maps that represent the most diverse conditions, to evalu-
to homogenize and to overlay the different maps. Once ate significant surface values in relation to the Posidonia
the total Posidonia coverage was obtained for the four dif- status. For the bootstrapping simulation, the study area
ferent periods (1959, 1980, 1990 and the present 2005), was divided into 2895 LUs. Each simulation was com-
the percentage decrease in the area occupied over time posed of 2895 steps: during the first step, one LU was
was estimated. selected randomly and the percentage of area of LU occu-
pied by Posidonia was measured. The second step added a
second random LU to the first one and the percentage of
Computer simulation
area occupied by Posidonia was measured as the sum of
The last objective of this work was to try to find a monit- the two LUs. During each of the subsequent steps, the
oring method that is the least expensive and at the same simulation randomly added LUs and measured the per-
time efficient in terms of estimating the area occupied by centage of area occupied by Posidonia. At the final step,
Posidonia. Given a reliable starting point, this monitoring the simulation considered all the 2895 LUs and measured
method would eliminate the need for full coverage sur- the percentage of area occupied by Posidonia in the sum
veys (SSS), and thus allow an easier and cheaper monitor- of all the LUs (i.e. we measured the total area of Posidon-
ing design. Ideally the sampling scheme should provide a ia in the three maps). Each step of the simulation was
reliable measure of the area of Posidonia with the lowest considered as a different sampling scheme. The first step
possible number of samples. Such a sampling scheme simulated a sampling scheme with only one LU, the sec-
would be useful in monitoring the conservation status of ond step a scheme with two LUs, and the last step one
Posidonia beds over time (by monitoring we mean a regu- with 2895 LUs covering the entire study area. For each of
lar activity of control in an area where the distribution of the three maps considered, the simulation was carried out
Posidonia has already been mapped and can be utilized as 50 times, giving a total of 144,750 steps for each map.
reference condition). Moreover, the ability to implement Using the results of the simulations, it was possible to
a low-cost up-to-date distribution in relation to historical build for each step (and for each map) the distribution of
coverage, could allow a valid examination of the coher- percentages. As an example, let us take the 1959 map: the
ence of the long-term conservation trends, and offer the simulation built the distribution of percentage areas occu-
chance for timely action. For this purpose, a GIS simula- pied by Posidonia when a sampling scheme with a single
tion of the sampling effort was carried out, considering LU was considered; the same was true up to 2895 LUs
the information collected by the towed video camera on and for the three maps. In this way, we calculated for
bottom strips as potentially useful sampling units of the each step (i.e. for each sampling scheme) the mean per
Posidonia surface. The aim was to calculate from a mini- cent area occupied by Posidonia and the associated stand-
mum surface coverage (the Landscape Unit) operated by ard deviation. As a reference, we considered reliable all
a towed video camera, the minimum level of information the sampling schemes that gave a standard deviation
that was enough to describe with high accuracy and pre- smaller than 5%, but all the distribution was calculated
cision the status of the beds in the different periods. The and any standard deviation value can be considered. The
complete information on the percentage presence of Posi- simulations were carried out in ArcGIS9 (ESRI) using an
donia was derived from the maps available. AML script.
Considering the characteristics of the data sets collected
using the towed video camera, each sampling unit, here-
Results
after called Landscape Unit (LU), was built as a north–
south oriented 10-m-wide strip (the same as the shooting The present day coverage of Posidonia beds has changed
coverage of the video camera), and limited by the coast- radically compared with the other reference periods
line (to the North) and by the depth of 35 m (to the (Fig. 2). In fact, an estimate of 2899 ha of Posidonia and
South), according to the different functional and mor- 1800 ha of dead matte was calculated for the 2005 survey.
302 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
For these three sub-areas, the trend in the reduction of
Posidonia coverage and the modification of the lower
limit were estimated and different conditions were found
(Fig. 3). In 1959, the lower limit of the Posidonia bed was
c. 35 m in the entire study area (Fusco 1961), but it had
markedly changed 20 years later (Ardizzone & Migliuolo
1982) with a mean value of c. 22–24 m in the most
regressed central area and 25 m east of Terracina. In the
1990 survey, the lower limit showed different conditions:
almost the same depth (c. 30–35 m) off Cape Circeo, 20–
22 m in the central part of the area, and 24–25 m east of
Terracina (Diviacco et al. 2001). In the present survey,
the Circeo area is the least modified one, while in the
central area the lower limit further decreased, reaching a
depth of 18–20 m. In the eastern area the present limit is
at 23–25 m.
The upper limit changed less than the lower one, going
from 14 m in 1959 to 17–18 m in the present study,
without any great diversification in the different sub-
areas. The only important exception is off the harbour of
Circeo. From the first estimate of Posidonia coverage of
7290 ha in 1959, the total area in 1980 had become
5054 ha, and 3581 ha in 1990 down to the present value
of 2899 ha. At the same time, no important increase in
the dead matte has been observed. We do not have any
information on the dead matte area in 1959 and 1980 but
a limited increase was observed in the last 10 years, com-
paring the estimated area of 1663 ha in the 1990 to the
present value of 1800 ha, when most of the regression
had already been observed.
The simulation of the different sampling schemes
showed different values in relation to the status of the
Posidonia meadows. The percentages of Posidonia meas-
ured considering the entire surface of the study area
were 69.39% in 1959, 34.31% in 1990 and 27.72% in
Fig. 2. The Posidonia oceanica meadows in the historical maps 2005. For the 1959 map that represents the best and
(1959: from Fusco 1961; 1980: from Ardizzone & Migliuolo 1982; the most regular condition, the simulation suggested
1990: from Diviacco et al. 2001), and in the 2005 survey (present that a sampling scheme with only nine randomly selec-
paper).
ted LUs provided the minimum possible effort for
obtaining a reliable estimate of the area of Posidonia. In
fact, nine randomly selected LUs gave a mean estimate
Three sub-areas, characterized by different conditions can of 70.05% of Posidonia with a standard deviation of
be identified (Fig. 2). The first sub-area (the westernmost 4.92%. In 1990, the minimum sampling effort required
one) is that off Cape Circeo where Posidonia beds were to estimate the condition of Posidonia was of 18 ran-
the least modified over the years. The second sub-area domly selected LUs, corresponding to a mean percent-
(the central one) is located between Cape Circeo and Ter- age of 34.91% with a standard deviation of 4.98%.
racina; here the Posidonia beds display the most consis- In 2005, 21 randomly selected LUs gave a mean of
tent regression in time. This coast has suffered from 27.42% with a standard deviation of 4.89% (Fig. 4). To
important urban change that influenced both water qual- reduce the standard deviation to a value of roughly 1%,
ity and sediment type. The third sub-area (the eastern- we need 221 LUs for 1959 (mean 69.16, SD 0.99%),
most one), located from Terracina to Sperlonga, showed 340 LUs for the 1990 distribution (mean 34.25, SD
a medium regressive status of the Posidonia beds, mainly 0.99%) and 480 LUs for the 2005 distribution (mean
characterized by the decreasing of their lower limits. 27.73, SD 0.99%).
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 303
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
Fig. 3. Trend of the Posidonia oceanica bed coverage (above) and of lower and upper limits of the Posidonia beds (below) in the 1959, 1980,
1990 and 2005 maps and in the different sub-areas.
The validation of old maps is a main test for their use-
Discussion
fulness (Leriche et al. 2004). The 1990 and the present
The very heterogeneous status of the Posidonia beds maps can be considered fully reliable, in our case the lat-
observed in the 30-km long study area stresses the need ter being implemented by SSS full coverage sonograms,
for large-scale studies to understand the complex level of validated by video camera and located by DGPS. The
modification, which is particularly important in cases of other old maps deriving from the interpolation of discrete
regression. The relatively rapid regression observed here data, are important for the upper and lower limits of
can be summarized in the reduction of the bottom cover- tidily distributed Posidonia.
age by c. 60% since 1959, 19% of which has occurred Contrary to the rapid regressive condition of the mea-
since the last survey dating back to 1990. The total loss of dow, the coverage of dead matte does not appear to be
Posidonia beds amounted to 4391 ha in the last 50 years. proportionally increasing. The reason for this lies in the
The extent of this loss is however different in the three structure of the matte. The low-lying matte of the study
main sub-areas. The zone off Cape Circeo showed a little area suffers from physical impact (trawl fishing) and
reduction of the overall surface and lower limits, probably heavy siltation. The dead matte, somewhat eroded and
because the seagrass meadows are located offshore and somewhat covered up by sediment, tends to disappear
therefore are less influenced by continental inputs. How- and therefore is detectable neither by SSS nor by video
ever, this area is also characterized by the presence of camera. The 1990 maps and present maps can explain
hard bottoms, that prevent damage as a consequence of this condition. These two maps have similar total dead
illegal coastal trawling. The exception is the zone immedi- matte surfaces (1663 and 1800 ha) but with different geo-
ately off the harbour of Circeo. This important coastal graphic position due to the shifting of the dead matte
harbour, realized in the 1960s, markedly modified the strip towards the lower Posidonia limit. This limit is mov-
Posidonia bed creating a big discontinuity in its distribu- ing towards the coastline, the new dead matte is following
tion that can be clearly seen from the first image to the the limit, and the old dead matte is disappearing, being
present condition (Fig. 2). eroded and covered by sediment.
The middle area showed the most dramatic coverage This current critical condition is not the result of cata-
and meadow limits reduction. As stated before, this area strophic pollution but is certainly due to the anthropo-
was subjected in the past years to different human genic modifications very common in almost every
impacts that lead to a heavy coastal erosion and turbidity Mediterranean coastal zone (Boudouresque et al. 2006).
of seawaters. Furthermore, an illegal trawling activity is Rapid growth of the human settlements, building of new
today carried out. Finally the third sub-area, from Terra- harbours and breakwaters, input of nutrient coming from
cina to Sperlonga, displayed a medium condition of mea- the intensive agriculture of the area, and the illegal trawl
dow extension and limits regression (Figs 2 and 4). This fishing still being carried on (Ardizzone et al. 2000), are
area is less subject to erosional phenomena, turbid water, without any doubt the joint causes of the observed regres-
illegal trawling and, more general, to human impacts. sions.
304 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
Mediterranean countries, as well. The general status of
regression reported in many scientific works is mainly
linked to spot information on the amount of dead matte
observed in a present day distribution, thus preventing
any evaluation of the dynamic trend of the meadow cov-
erage. But this problem is not only a Mediterranean one.
As reported by Short & Wyllie-Echeverria (1996) ‘a realis-
tic estimate of present seagrasses loss worldwide is not
possible and the few available quantitative reports are cer-
tainly an underestimate of overall loss’. Australia, the
most important continent as to the number of species of
seagrasses and sea bottom coverage, is reported to be
endangered for some species, which have regressed by
45,000 ha in 11 sites (Walker & McCombe 1992), but is
this an important area in relation to the overall amount
of Australian seagrasses or is it negligible? We cannot
answer this question. A similar question is that of the
90,000 ha loss reported for the worldwide decline (Short
& Wyllie-Echeverria 1996).
The results obtained with the simulations for the three
different maps of the Posidonia beds over time showed
that significant information can be obtained on the status
of a meadow already mapped, with a limited sampling
effort and with high accuracy and precision (SD < 5%)
being yielded in the description of the Posidonia surface.
The sampling effort necessary to reach 1% of the standard
deviation value is very high (respectively 221, 340, 480
LUs) and therefore the objective of low cost monitoring
is lost. With only 9, 18, and 21 LUs, we obtained a good
description of the bottom coverage in 1959, 1990, and
2005, respectively, with a 5% standard deviation value.
Moreover, it is evident that the number of the minimum
LUs samples increased in time, as the more regular is the
Posidonia distribution, as in the case of the oldest map,
the more limited is the sampling effort needed. The sur-
Fig. 4. Average percentage of Posidonia oceanica coverage ±SD face percentage covered by the towed video camera,
obtained from GIS simulation for the 1959, 1990 and 2005 maps. which is useful to describe the whole Posidonia distribu-
tion, amounted therefore to 0.3% of the total area for the
1959 map, 0.6% for that of 1990 and 0.7% for the 2005
Evidence of the connection between coastal modifica- one.
tion and regression of Posidonia can be found also when Modern techniques to produce Posidonia bed carto-
comparing the described Posidonia to the status of the graphy at a vast macro-scale are nowadays very
Posidonia meadows in the Pontine Islands, just off the advanced and include different kinds of surveys (SSS,
study area. None of the above mentioned impact factors video camera or ROV, diving), data analysis and GIS
is present in those islands and the Posidonia coverage of elaboration. Their cost is anyhow still very expensive.
the sea bottom is stable, and certainly has been so in the While an initial important effort to obtain detailed refer-
last 15 years (G.D. Ardizzone 1991, unpublished observa- ence cartography for each Posidonia meadow is under-
tions 2005), and without any sign of modification such as standable, the same effort is not feasible and realistic in
the presence of dead matte. a regular monitoring programme. The evidence of
A good knowledge of the Posidonia distribution but at reduction in survey costs with these limited sampling
the same time little well-documented information on his- surfaces could allow the planning of regular monitoring
torical modification of the meadows is the present general programmes implemented by towed video camera sys-
condition of the Italian coastal areas and that of other tems. The costs of these instruments is relatively low,
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 305
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
their use is very simple, needing small craft and a posi-
Acknowledgements
tioning system by means of GPS or DGPS implemented
by a plotter system. Sampling units orthogonal to the This study has been realized thanks to the financial con-
coast, which are useful to estimate significant portions tributions of Latium Regional Administration.
of seagrass beds, should always be adopted and the need
for a stratified sampling design should be considered in
References
the allocation of the random LUs when different charac-
teristics of the distribution are present. Ardizzone G.D. (1991) Cartografia bentonica con sistemi video
This kind of survey is currently being used to validate controllati a distanza. Oebalia, XVII(Suppl), 421–452.
aerial photographs or SSS sonograms for the correct iden- Ardizzone G.D., Migliuolo A. (1982) Modificazioni di una pra-
tification of unidentified patches. The experience already teria di Posidonia oceanica (L.) Delile del Medio Tirreno sot-
obtained evidenced the potentiality of towed underwater `
toposta ad attivita di pesca a strascico. Naturalista Siciliano,
video surveys to monitor very large and already mapped S. IV VI(Suppl. 3), 509–515.
Posidonia beds with limited and low-cost surveys. Ardizzone G.D., Pelusi P. (1984) Yield and damage evaluation
of bottom trawling on Posidonia meadows. In: Boudou-
resque C.F., Jeudy de Grissac A. Oliver J. (Eds), First Inter-
Summary national Workshop on Posidonia oceanica Beds. GIS
Posidonie Publ., France: 1, 63–72.
During a monitoring work along the Latium coast (Cen-
Ardizzone G.D., Tucci P., Somaschini A., Belluscio A.
tral Tyrrhenian Sea) a detailed cartography of Posidonia
(2000) Is bottom trawling responsible for the regression
oceanica beds was implemented by means of SSS and
of Posidonia oceanica meadows in the Mediterranean Sea?
towed video camera techniques in 2005. This cartography In: Kaiser M.J., Groot de S.J. (Eds), Effects of Fishing on
has been compared with several historical maps dating Non-target Species and Habitats. Blackwell Science, Oxford,
back over the last 50 years (1959, 1980 and 1990). More- UK: 37–46.
over, using bootstrap simulations, we were able to obtain Badalamenti F., Di Carlo G., D’Anna G., Gristina M., Toccaceli
the percentage of sea bottom that should be assessed to M. (2006) Effects of dredging activities on population
understand the change in relation to a reference condi- dynamics of Posidonia oceanica (L.) Delile in the Mediterra-
tion. In 1959, the lower limit of the Posidonia bed was nean sea: the case study of Capo Feto (SW Sicily, Italy).
around 35 m in the entire study area. Only 20 years later Hydrobiologia, 555, 253–261.
the value was around 22–24 m, while in the 1990 survey Balestri E., Cinelli F., Lardicci C. (2003) Spatial variation in
the lower limit was at 20–22 m, and in 2005 it was Posidonia oceanica structural, morphological and dynamic
reduced to 18–20 m depth. The total area of Posidonia features in a northwestern Mediterranean coastal area: a
changed from 7290 ha in 1959 to 5054 ha in 1980, and multi-scale analysis. Marine Ecology Progress Series, 250,
from the 3581 ha in 1990 down to the current value of 51–60.
2899 ha, to a total loss of about 60%. The current critical Balestri E., Benedetti Cecchi L., Lardicci C. (2004) Variability
condition is due to anthropogenic modifications very in patterns of growth and morphology of Posidonia oceanica
common in almost every Mediterranean coastal zone. exposed to urban and industrial wastes: contrasts with two
Computer simulations were made on the three maps reference locations. Journal of Experimental Marine Biology
(1959, 1990, 2005) that represent the most diverse condi- and Ecology, 308, 1–21.
Ballesta L., Pasqualini V., Pergent G., Pergent-Martini C.
tions. Sampling units (Landscape Units, LUs) were set up
(2000) Distribution and dynamics of Posidonia oceanica beds
as a north–south oriented strip 10 m wide, and limited
` ´
along the Alberes coastline. Academie de Sciences/Editions
by the coastline and by the 35 m depth. The results
´
scientifiques et medicales. Life Sciences, 323, 407–414.
obtained with the simulations showed that significant
Bianchi C.N., Ardizzone G.D., Belluscio A., Colantoni P.,
information could be obtained on the status of a mea-
Diviacco G., Morri C., Tunesi L. (2003) La cartografia del
dow already mapped, with a limited sampling effort and benthos. In: Gambi M.C., Dappiano M (Eds), Manuale di
yielding a 95% significant description of the Posidonia metodologie di campionamento e studio del benthos marino
surface. With only 9, 18 and 21 LUs, respectively, we mediterraneo. Biologia Marina Mediterranea, 10(Suppl.),
obtained a good description of the bottom coverage in 367–394.
the three periods 1959, 1990 and 2005. The evidence of Borum J., Duarte C.M., Krause-Jensen D., Greve T.M.
reduction of survey costs with these limited sampling (2004) European Seagrasses: An Introduction to Monitoring
surfaces could allow the planning of regular monitoring and Management. EU Project Monitoring and Managing
programmes implemented by towed video camera sys- of European Seagrasses (M&MS) EVK3-CT-2000-00044:
tems. 95 pp.
306 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
Boudouresque C.F. (2004) Marine biodiversity in the Mediter- Francour P., Ganteaume A., Poulain M. (1999) Effects of boat
ranean: status of species, populations and communities. anchoring in Posidonia oceanica seagrass beds in the Port-
Scientific Report of Port-Cros national Park, 20, 97–146. Cros national Park (north-western Mediterranean Sea).
Boudouresque C.F., Bernard G., Bonhomme P., Charbonnel Aquatic Conservation: Marine and Freshwater Ecosystems, 9,
E., Diviacco G., Meinesz A., Pergent G., Pergent-Martini C., 391–400.
Ruitton S., Tunesi L. (2006), Preservation et conservation des Fusco N. (1961) Carta da Pesca n. 3. Da Capo Circeo a Capo
herbiers a Posidonia oceanica. RAMOGE Pub., France: pp. Miseno. Ministero Marina Mercantile. Direzione Generale
1–202. Pesca Marittima.
´
Bourcier M. (1989) Regression des herbiers a Posidonia ocea- `
Gallegos M., Merino M., Marba N., Duarte C.M. (1993) Bio-
´
nica (L.) Delile a l’Est de Marseille, sous l’action conjuguee mass and dynamics of Thalassia testudinum in the Mexican
des activities humaines et des modifications climatiques. In: Caribbean: elucidating rhizome growth. Marine Ecology Pro-
Boudouresque C.F., Meinesz A., Fresi E., Gravez V. (Eds), gress Series, 95, 85–192.
Second International Workshop on Posidonia oceanica beds 2. Gambi M.C., Dappiano M., Lorenti M., Iacono B., Flagella S.,
GIS Posidonie Publ., France: 287–292. Buia M.C. (2005) ‘‘Chronicle of a death foretold’’ – features
Brown C.J., Cooper K.M., Meadows W.J., Limpenny D.S., Rees of a Posidonia oceanica bed impacted by sand extraction. In:
H.L. (2002) Small scale mapping of sea bed assemblages in ¨
Ozhan E. (Ed), Proceedings of the Seventh International Con-
the eastern English Channel using sonar and remote samp- ference on the Mediterranean Coastal Environment, MED-
ling techniques. Estuarine Coastal and Shelf Science, 54, 263– COAST 05, 25–29 October 2005. Kusadasi, Turkey: 441–450.
278. `
Garcia-Charton J.A., Bayle J.T., Sanchez-Lizaso J.L., Chiesa P.,
Carleton J.H., Done T.J. (1995) Quantitative video sampling of ` ´
Llaurado C., Perez C., Djian H. (1993) Respusta de la pra-
coral reef benthos: large-scale application. Coral Reefs, 14(1), dera de Posidonia oceanica y su ictiofauna asociada al anclaje
35–46. de embarcaciones en el parque Nacional de Port Cros, Fran-
Cinelli F., Pardi G., Papi I., Benedetti Cecchi L. (1995) Mappa- cia. Publication Especial del Instituto Espanol de Oceanografia,
tura delle praterie di Posidonia oceanica (L.) Delile intorno 11, 423–430.
`
alle isole minori dell’Arcipelago Toscano. Atti Societa Tos- Garrabou J., Riera J., Zabala M. (1998) Landscape pattern
cana Scienze Naturali, 102, 93–110. indices applied to Mediterranean subtidal rocky benthic
Colantoni P., Gallignani P., Fresi E., Cinelli F. (1982) Patterns communities. Landscape Ecology, 13, 225–247.
of Posidonia oceanica (L.) Delile beds around the island of Gili J. M., Ros J. (1985) Study and cartography of the benthic
Ischia (Gulf of Naples) and adjacent waters. P.S.Z.N.I: Mar- communities of Medes Islands (NE Spain). P.S.Z.N.I: Mar-
ine Ecology, 3 (1), 53–74. ine Ecology, 6(3), 219–238.
De Falco G., Murru E., Baroli M., Piergallini G., Cancemi G. Guidetti P., Fabiano M. (2000) The use of lepidochronology to
(2000) Photo aerial image processing and sediment analysis assess the impact of terrigenous discharges on the primary
as indicators of environmental impact on Posidonia oceanica leaf production of the Mediterranean seagrass Posidonia
in the Mediterranean. Biologia Marina Mediterranea, 7(2), oceanica. Marine Pollution Bulletin, 40, 449–453.
349–352. Hemminga M.A., Duarte C. (2000) Seagrass ecology. Cam-
Delgado O., Grau A., Pou S., Riera F., Massuti C., Zabala M., bridge University Press, Cambridge: 298 pp.
Ballesteros E. (1997) Seagrass regression caused by fish cul- Kendrick G.A., Eckersley J., Walker D.I. (1999) Landscape-
tures in Fornells Bay (Menorca, Western Mediterranean). scale changes in seagrass distribution over time: a case study
Oceanologica Acta, 20, 557–563. from Success Bank, Western Australia. Aquatic Botany, 65,
´
Delgado O., Ruiz J.M., Perez M., Romero J., Ballesteros E. 293–309.
(1999) Effects of fish farming on seagrass (Posidonia oceanic- Kleijnen J.P.C., Feelders A.J., Cheng R.C.H. (1998) Bootstrap-
a) in a Mediterranean bay: seagrass decline after organic ping and validation of metamodels in simulation. In: Medei-
loading cessation. Oceanologica Acta, 22(1), 109–117. ros D.J., Watson E.F., Carson J.S., Manivannan M.S. (Eds),
Diviacco G., Spada E., Virno Lamberti C. (2001) Le Fanero- Proceedings of the 1998 Winter Simulation Conference,
game marine del Lazio. Descrizione e cartografia delle praterie December 13–16, 1998, Washington, DC, USA. 701–706.
di Posidonia oceanica e dei prati di Cymodocea nodosa. Lathrop R.G. Jr, Bognar J.A. (1998) Applying GIS and
Quaderno ICRAM, Roma: 113 pp. landscape ecological principles to evaluate land conserva-
Duarte C.M. (2002) The future of seagrass meadows. Environ- tion alternatives. Landscape and Urban Planning, 41,
mental Conservation, 29, 192–206. 27–41.r.
Falconetti C., Meinesz A. (1989) Charting the seaward limit of Leriche A., Boudouresque C.F., Bernard G., Bonhomme P.,
Posidonia oceanica meadows and of circalittoral biocoenoses Denis J. (2004) A one-century suite of seagrass bed maps:
along the coast of Monaco. Oceanologica Acta, 12 (4), 443– can we trust ancient maps? Estuarine Coastal and Shelf
447. Science, 59, 353–362.
Forman R.T.T., Gordon M. (1986) Landscape Ecology. Wiley, Leriche A., Pasqualini V., Boudouresque C.F., Bernard G.,
New York: 619 pp. Bonhomme P., Clabaut P., Denis J. (2006) Spatial, temporal
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 307
Change in a Posidonia oceanica beds Ardizzone, Belluscio & Maiorano
and structural variations of a Posidonia oceanica seagrass photogrammetry, and GIS techologies in seagrass mapping.
meadow facing human activities. Aquatic Botany, 84, 287– Photogrammetric Engineering & Remote Sensing, 67, 99–105.
293. Pasqualini V., Pergent-Martini C., Pergent G. (1999) Environ-
`
Marba N., Duarte C.M. (1994) Growth response of the sea- mental impact identification along the Corsican coast
grass Cymodocea nodosa to experimental burial and erosion. (Mediterranean Sea) using image processing. Aquatic Botany,
Marine Ecology Progress Series, 107, 307–311. 65, 311–320.
`
Marba N., Duarte C.M. (1997) Interannual changes in seagrass ´ `
Peres J.M., Picard J. (1964) Nouveau manuel de bionomie
(Posidonia oceanica) growth and environmental changes in ´ ´
benthique de la Mer Mediterranee. Recueil des Travaux de la
the Mediterranean littoral zone. Limnology and Oceanogra- Station Marine d’Endoume, 31, 1–137.
phy, 42, 800–810. ´ ` ´
Peres J.M., Picard J. (1972) Causes de la rarefaction et de
`
Marba N., Duarte C.N., Cebrian J., Enriquez S., Gallegos E., la disparition des herbiers de Posidonia oceanica sur les
Olesen B., Sand-Jensen K. (1996) Growth and population ´ ´
cotes francaises de la Mediterranee. Aquatic Botany, 1,
dynamics of Posidonia oceanica on the Spanish Mediterra- 133–139.
nean coast: elucidating seagrass decline. Marine Ecology Pergent-Martini C., Pergent G. (1995) Impact of a Sewage
Progress Series, 137, 203–213. Treatment Plant on the Posidonia oceanica meadow: assess-
´
Meinesz A., Laurent R. (1978) Cartographie et etat de la limite ment criteria. Proceedings of the Second International Confer-
´
inferiore de l’herbier de Posidonia oceanica dans les Alpes- ence on the Mediterranean Coastal Environment MEDCOAST
maritimes (France). Campagne Poseidon 1976. Botanica ‘95: 1389–1399.
Marina, 21 (8), 513–526.e Pergent-Martini C., Pergent G. (1996) Spatio-temporal dynam-
Meinesz A., Belsher T., Thibaut T., Antolic B., Ben Mustapha ics of Posidonia oceanica beds near a sewage outfall (Medi-
K., Boudouresque C.-F., Chiaverini D., Cinelli F., Cottalorda terranean – France). In: Kuo J., Phillips R.C., Walker D.I.,
J.M., El Abed A., Orestano C., Grau A.M., Ivesa L., Jaklin A., Kirkman H. (Eds), Seagrass Biology: Proceedings of an inter-
Langar R.H., Massuti-Pascual E., Peiraino A., Tunesi L., national workshop. Faculty of Sciences, University of Western
De Vaugelas J., Zavodnik N., Zuliejevic A. (2001) The intro- Australia, Australia: 229–306.
duced green alga Caulerpa taxifolia continues to spread in the Piazzi L., Acunto S., Cinelli F. (2000) Mapping of Posidonia
Mediterranean. Biological Invasion, 3, 201–210. oceanica beds around Elba Island (western Mediterranean)
`
Meinesz A., Lefevre J.R., Astier J.M. (1991) Impact of coastal with integration of direct and indirect methods. Oceanolog-
development on the infralittoral zone along the southern ica Acta, 23 (3), 339–346.
Mediterranean shore of continental France. Marine Pollution Procaccini G., Buia M.C., Gambi M.C., Perez M., Pergent G.,
Bulletin, 23, 343–347. Pergent-Martini C., Romero J. (2003) The Seagrass of the
Millier I.R., Muller R. (1999) Validity and reproducibility of Western Mediterranean. In: Green E.P., Short F.T. (Eds),
benthic cover estimates made during broadscale surveys of World Atlas of Seagrasses. University of California Press,
coral reefs by mantra tow. Coral Reef, 18, 353–356. Berkeley, CA, USA, 48–58.
Ministero dell’Ambiente e del Territorio (2003) Completamento Regione Lazio (2004) Il Progetto BeachMed: Recupero ambi-
delle conoscenze naturalistiche di base. Descrizione di base in entale e mantenimento dei litorali in erosione con l’utilizzo
scala 1:250,000 delle biocenosi marine costiere. Ministero di depositi sabbiosi marini. 3° Quaderno Tecnico, Fase C.
dell’Ambiente. Servizio Conservazione della Natura, ConS- Convenzione 2002-01-4.3-I-028. Regione Lazio Direzione
CN250. `
Generale Ambiente e Protezione Civile – Comunita Europea:
Montefalcone M., Albertelli G., Bianchi C.N., Mariani M., 275 pp.
Morri C. (2006) A new synthetic index and a protocol for Relini G. (1999) L’Italia e la protezione della biodiversita`
monitoring the status of Posidonia oceanica meadows: a in Mediterraneo. Biologia Marina Mediterranea, 6 (1),
case study at Sanremo (Ligurian Sea, NW Mediterranean). 151–171.
Aquatic Conservation: Marine & Freshwater Ecosystems, 16, Ruiz J.M., Romero J. (2003) Effects of disturbances caused by
29–42. coastal constructions on spatial structure, growth dynamics
Norris J.G., Wyllie-Echeverria S., Mumford T., Bailey A., and photosynthesis of the seagrass Posidonia oceanica.
Turner T. (1997) Estimating basal area coverage of subtidal Marine Pollution Bulletin, 46, 1523–1533.
seagrass beds using underwater videography. Aquatic Botany, ´
Ruiz J.M., Peres M., Romero J. (2001) Effect of fish farm loa-
58(3–4), 269–287. dings on seagrass (Posidonia oceanica) distribution, growth
Pasqualini V., Pergent Martini C., Clabaut P., Pergent G and photosynthesis. Marine Pollution Bulletin, 42(9), 749–
(1998) Mapping of Posidonia oceanica using aerial photo- 760.
graphs and side scan sonar: application off the Island of `
Sanchez-Jerez B., Ramon-Espla A.A. (1996) Detection of envi-
Corsica (France). Estuarine Coastal and Shelf Science, 47, ronmental impacts by bottom trawling on Posidonia
359–367. oceanica (L.) Delile meadows: sensitivity of fish and macro-
Pasqualini V., Pergent-Martini C., Clabaut P., Marteel E., benthic communities. Journal of Aquatic Ecosystem Health, 5,
Pergent G. (2001) Integration of aerial remote sensing, 239–253.
308 Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd
Ardizzone, Belluscio & Maiorano Change in a Posidonia oceanica beds
´
Sanchez-Lizaso J.L., Guillen J.E., Ramos A. (1990) The regres- UNEP (1989) State of the Mediterranean marine environment.
sion of Posidonia oceanica meadows in El Campello (Spain). Athens, Greece. MAP Technical Report Series, 28, 48 pp.
´ ´
Rapports et Proces-Verbaux des Reunions de la Commission UNEP (1996) Etat du milieu marin et littoral de la Region
´
internationale pour l’Exploration scientifique de la Mediterra- ´ ´
mediterraneenne. UNEP. MAP Technical Report, 101, 1–148.
`
nee, 32, 7. Walker D.I., McCombe A.J. (1992) Seagrass degradation in
Short F.T., Coles R.G. (2001) Global Seagrass Research Meth- Australian coastal waters. Marine Pollution Bulletin, 25,
ods. Elsevier Science Publishers B.V., Amsterdam, 482 pp. 191–195.
Short F., Wyllie-Echeverria S. (1996) Natural and human Zharikov Y., Skilleter G.A., Loneragan N.R., Taranto T.,
induced disturbance of seagrasses. Environmental Conserva- Bronwyn E.C. (2005) Mapping and characterising
tion, 23 (1), 17–27 subtropical estuarine landscapes using aerial photogra-
Turner M.G. (1989) Landscape ecology: the effect of pattern phy and GIS for potential application in wildlife conserva-
on process. Annual Review of Ecology and Systematics, 20, tion and management. Biological Conservation, 125, 87–
171–197. 100.
Marine Ecology 27 (2006) 299–309 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd 309