Journal of Coastal Research 295-305 Royal Palm Beach, Florida Spring 2000

Seditnentological Parameters and Seagrasses Distributions as Indicators of Anthropogenic Coastal Degradation at Monterosso Bay (Ligurian Sea, NW Italy) William Cavazza,] Francesco Immordino.j Lorenzo Moretti.j Andrea Peirano,* Angela Pironi,§ Federica Ruggiero§ tCenter for Advanced Studies :j:ENEA Bologna *ENEA Marine Environment §Department of Earth and of Geodynamics Via Don Fiammelli 2 Research Center Geoenvironmental Sciences University of Basilicata 40138 Bologna, Italy P.O. Box 316 University of Bologna Via Anzio 10 19100 La Spezia, Italy Piazza di Porta San Donato 1 85100 Potenza, Italy 40126 Bologna, Italy

ABSTRACT .

CAVAZZA, W.; IMMORDINO, F.; MORETTI, L.; PEIRANO, A.; PIRONI, A., and RUGGIERO, F., 2000. Sedimento­ .tllllllll:. logical Parameters and Seagrasses Distributions as Indicators of Anthropogenic Coastal Degradation at Monterosso ~ Bay (Ligurian Sea, NW Italy). Journal of Coastal Research, 16(2),295-305. Royal Palm Beach (Florida), ISSN 0749­ 0208. ~~ eusss7.J -+; b-JW This paper illustrates an integrated physical-biological approach to investigate the effects on the coastal envi­ ronment of the construction of a large embankment along the shore of Monterosso Bay, NW Italy. The embank­ ment protrudes from the natural shoreline for more than 100 meters and has deflected the longshore current toward the offshore, as indicated by grain-size and mineralogical areal distributions of bottom sediments, and by the orientation of bedforms. Consequently, the downcurrent portion of the beach relative to the embankment has become sediment-starved and the site of finer-grained sedimentation, and severe shoreline retreat has oc­ curred, as indicated by sequential analysis of topographic maps and by the comparison of non-parametric pho­ tographs. This trend is recorded by the areal distribution of two seagrasses (marine phanerogams) along the bay: Posidonia oceanica - whose slow growth requires stable environmental conditions and a preference for coarse-grained sandy substratum-is present as dense and healthy meadows in the upcurrent portion of the bay whereas Cymodocea nodosa-an opportunistic, pioneer species capable of surviving in stressful environments­ is present only along the downcurrent (eastern) portion of the bay where it is replacing a progressively retreating Posidonia meadow. This is substantiated by (i) direct underwater observation of the remnants of a dead P. oceanica meadow along the eastern portion of the bay and (ii) interviews with the local population pointing to a more extensive Posidonia meadow along the eastern portion of the bay prior to the construction of the embank­ ment. Thus, biological parameters such as the density and health of marine phanerogams match physical pa­ rameters (grain-size distribution patterns) more traditionally employed in coastal studies and can provide sig­ nificant clues on both natural and anthropogenic medium-term coastal dynamics.

ADDITIONAL INDEX WORDS: Beach erosion, GIS, mineralogical tracers, sediment grain-size, coastal sedimentology.

INTRODUCTION logical mapping and those derived from (1) the grain-size and mineralogical analyses of bottom sediments to delineate the The coastal environment is the result of complex interac­ sediment dispersal pattern within the bay, (2) direct and in­ tions between physical and biological agents and processes, direct observations of bedforms to define the predominant including also the results of human activities. In spite of the orientation of waves and currents, and (3) the sequential obviousness of this statement, very few coastal studies are truly multidisciplinary and also often fail to develop appro­ analysis of aerophotographs and topographic maps to deter­ priately their application to shoreline management. This pa­ mine the shoreline change during the last century. The re­ per presents a case study covering Monterosso Bay, in the sults of these analyses are applied to an evaluation of the coastal region of Liguria (northwestern Italy). It has been environmental impact of a large embankment built along the developed from work originally financed by ENEA (Ente per shore of Monterosso Bay. The multidisciplinary approach le Nuove Tecnologie, l'Energia e l'Ambiente) and focused on adopted in this study has provided useful insights on coastal mapping the density and health of marine phanerogams evolutionary trends at Monterosso Bay and it is potentially meadows along the Ligurian coast (BIANCHI and PEIRANO, of wider significance and application. GIS technology was ex­ 1995). This study integrates old and new results of the bio- tensively employed to examine and compare the variance of the numerous physical and biological parameters measured 9824 received 7 August 1998; accepted 7 June 1999. over the study area and has proven itself intrinsically suited 296 Cavazza et al.

• -• • • lP.\rit::l\) 1\ ti • • • -.../• • • • -\ -, 5, • • ~\,10.. , north •\' 15 A 20

\ 25

30~ • rock samples ...beach samples • marine samples ~urban area LIGURIAN SEA

1Jo 2do 3do 4do sod m

Figure 1. Location of Monterosso Bay (inset, upper left), bathymetric-topographic map and location of rock and sediment (beach and marine) samples.

to the complex, multidisclipinary nature of this kind of en­ and 90 meters wide (Figures 1, 2). Dumping took place in vironmental study. several phases from 1963 to 1970. In recent years, large lime­ stone blocks were used in the attempt to strengthen the mar­ MONTEROSSO BAY gins of the protruding embankment. Monterosso Bay is located within the Cinque Terre of In order to identify the effects on the environment of the northwestern Italy (Figure 1), a small coastal area of about construction of the embankment, it was decided to study the 36 sq. kms of high environmental value which was recently Monterosso Bay from Punta (Cape in Italian) Mesco to Punta granted the status of national park. The name Cinque Terre Corone, thus delimiting a stretch of coast about 2.5 km long. means "five villages" and refers to the existence of five small These two capes were chosen as boundaries of the study area coastal communities totaling a population of about 5,300 peo­ because they are significant coastal promontories, most likely ple (1975 census). The economy of the Cinque Terre is largely to delimit a littoral cell characterized by relatively homoge­ dependent on tourism. This is particularly true for the village neous physical processes. of Monterosso al Mare which has the only significant beach The Monterosso Bay drainage basin covers an area of 6.36 of the area and attracts a large number of tourists. In the km 2 and reaches a maximum elevation of 619 meters above 1960s the railroad line running along the coast was doubled, sealevel. Overall, the topography is very steep; three short, and part of the material extracted during the widening of a ephemeral creeks drain the basin. The western portion of the railroad tunnel near Monterosso al Mare was utilized for the bay (from Punta Mesco to the marina) is characterized by construction of a parking lot to be used by the tourists. To steep cliffs with abundant talus deposits, whereas the central this end, the detritus was dumped in a site along the Mon­ and eastern portions are characterized by relatively gentler terosso beach to form an embankment about 150 meters long slopes. The bathymetry mimics the topography on land, as

Journal of Coastal Research, Vol. 16, No.2, 2000 Coastal Degradation at Monterosso Bay, NW Italy 297

Monterosso drainage basin is characterized by sedimentary rocks covering 58% of the drainage basin. This third outcrop belt consists predominantly of regularly interbedded fine­ grained sandstone and mudrock layers, with subordinate out­ crops of chert. Talus, alluvium and beach deposits represent together the remaining 3% of the drainage basin. The study area is characterized by both linear and point sources of sediment. The actively eroding western cliffs (DE STEFANIS et al., 1978 ) provide a large mass of detritus, as indicated by poorly sorted debris aprons prograding directly into the sea. On the other hand, the mouths of three small creeks seem to provide point-sourced and sporadic detrital input to the bay. They are located on both sides of the em­ bankment and along the small beach in front of the old town (Figure 1). No hydrographic measurements on these streams are available; nevertheless, interviews with the Monterosso inhabitants have pointed to their extremely low water dis­ charge. No measurements of wind, wave, or nearshore current ori­ entation and velocity are available for Monterosso Bay, al­ though the records available for the Palmaria Island field station of the Italian Navy, located about 18 km SE of the study area, indicate that during major storms wind and waves travel towards the northeast (Istituto Idrografico della Marina, 1978). Similarly, no determination of the net littoral drift at Monterosso Bay was available before this study was made.

MARINE PHANEROGAMS AT MONTEROSSO BAY

The importance of seagrasses (marine phanerogams) in the maintenance of coastal equilibrium, both from the biological and the physical viewpoint, is accepted worldwide (e.g . Bou­ Figure 2. View towards the east of Monterosso Bay. Note beach progra­ DOURESQUE and MEISNEZ, 1982; STEVENSON, 1988; WALK­ dation on the western (upcurrent) side of the embankment. The St. Cris­ ER, 1989 ). Once thought to contribute little to the marine toforo promontory (background) covers most of the old town of Monterosso ecosystem, it is now well established that seagrasses are im­ al Mare. portant producers of biomass and oxygen, provide food for grazers and detritus feeders, and represent nursery and feed­ ing grounds for numerous species of fish and crustaceans, seafloor gradients gen erally decrease going from west to east including many commercially valuable taxa. within the bay (Figure 1). Two taxa of seagrasses are common at Monterosso Bay: In spite of its small area, the Monterosso Bay drainage Posidonia oceanica (L.) Delile and Cymodocea nodosa (U cria) basin comprises outcrops of a variety of rock types. These Ascherson. The two plants are endemic to the Mediterranean include, in order of decreasing abundance, mudrock (silt­ Sea, where they form large meadows mostly on loose sub­ stone, mudstone and shale), sandstone, gabbro, serpentinite, stratum down to water depth of about 40 and 20 meters, re­ and minor amounts of limestone and chert (Figure 3, Table spectively. P. oceanica typically forms very thick meadows 1)(SOCIETA GEOLOGICA ITALIANA, 1994 ). From southwest to characterized by a very dense network of rhizomes capable northeast, three coherent outcrop belts can be recognized. of trapping large amounts of sedimentary matter with which The westernmost one is characterized by sedimentary rocks, it forms compact beds (mattes) that can reach several meters mostly coarse grained, poorly cemented sandstone and in­ in height. The leaves have a dampening effects on wave and durated shale. This outcrop belt covers about 13% of the current energy levels and are thought to contribute to shore­ whole drainage basin of Monterosso Bay but nonetheless line protection (e.g . BLANC and JEUDY DE GRISSAC, 1984). seems to provide a significant sedimentary input to the bay During winter time, thick accumulations of dead leaves (ban­ because of frequent rockfalls down the steep cliffs. The second quettes) washed to the shore provide additional protection outcrop belt (26% of the drainage basin) is characterized by from beach erosion. P. oceanica is a slow-growth species which distinctive ophiolitic rocks, i.e. a coarse-grained gabbro com­ prefers stable environmental conditions. It has an average posed of approximately equal amounts of plagioclase and py­ biomass growth of 38 t/ha per year (dry weight) and an oxy­ roxene and a massive serpentinite . The eastern portion of the gen production ranging between 4 and 20 liters/m" per day;

Journal of Coastal Research, Vol. 16, No.2, 2000 298 Cavazza et al.

DRAINAGE BASIN LITHOLOGY 70-

50-

30-

10­ %

Sedimentary D rocks • Gabbro • Serpentinite • Other

Sandstone iE Shale, siltstone and limestone ~ Serpentinite ~Gabbro t:-:-:-:-:-:-:·:l Shale and siltstone lIIIJIllJ Sandstone and mudstone ~Chert c:=J Alluvial and beach deposits

r------,....--~ o 500 1000 m

Figure 3. Geological map of the Monterosso Bay drainage basin (modified from ABBATE, 1969, and REGIONE LIGURIA, 1979). Inset (upper left) shows lithologic composition (areal percentages) of the drainage basin and mineralogical-petrologic composition (modal percentages) of twenty-eight marine and beach sediment samples taken within the bay. Note the enrichment in ophiolite-derived detritus (gabbro and serpentinite) in the sediment of the bay.

more than 400 algae and 1000 animal species live in P ocean­ ly a pioneer species and may tend to progressively replace P ica meadows (BOUDOURESQUE and MEISNEZ, 1982). oceanica in areas of high environmental stress (see PEIRANO The overall characteristics of C. nodosa are similar to those and BIANCHI, 1995, and BRIVIO, 1996, for references). of P oceanica, but the former species forms markedly less dense meadows, has a less developed rhizome system and can METHODS withstand more stressful environmental conditions, including General also a finer-grained substratum (BUIA et al., 1992; PIRC et al., 1993). Because of this adaptability, C. nodosa is common- This study is based on the determination of the areal dis­ tribution of a number of variables over Monterosso Bay: to­ pographic and bathymetric gradients, rock units cropping out Table 1. Areal percentages of rock types in the Monterosso Bay drainage in the drainage basin, grain-size distribution and mineral­ basin. ogical composition of beach and nearshore sediment, abun­ dance and state of health of seagrasses, and shoreline posi­ Rock type Area (km") Area (%) tion through time. To rigorously analyze and compare these Serpentinite 0.44 6.92 variables, a geographic information system (GIS) was em­ Gabbro 1.24 19.50 Sandstone 1.77 27.90 ployed. First, an integrated topographic-bathymetric base Mudrock with minor limestone 2.72 42.69 map of the study area was created by digitizing the maps of Chert 0.03 0.47 REGIONE LIGURIA (1979) and GONGORA GONZALES (1994) Talus, alluvium, and beach deposits 0.16 2.52 with the help of the software program AutoCad" v. 12. The 100.00 Total 6.36 file thus obtained was then exported to the program Mini-

Journal of Coastal Research, Vol. 16, No.2, 2000 Coastal Degradation at Monterosso Bay, NW Italy 299

CadO'O v. 6.0.4 and, with Contours Pro" v. 1.3.5, a series of vations were made at 355 locations along fourteen transects layers containing the areal distribution of the variables listed oriented perpendicular to the shore. At each location, the na­ above was created. The analysis of coastline change was per­ ture, density, and state of health of the phanerogam meadows formed using Maplnfo'" v. 3.0. Ultimately, more than 60 lay­ were recorded. ers were created; only the information relevant to the subject of this paper has been included here. Coastline Analysis To determine the temporal evolution of the coastline at Sediment Grain-Size Analysis Monterosso Bay the two most accurate topographic maps Ninety-eight beach and seafloor grab samples were taken available (ISTITUTO GEOGRAFICO MILITARE, 1938; REGIONE within the bay along fourteen transects perpendicular to the LIGURIA, 1979) were compared. These maps cover a time shore (Figure 1); seafloor samples were taken during SCUBA span of about 40 years straddling the period of the construc­ dives. Each sample was washed with distilled water in order tion of the embankment (1963-70). The two maps were dig­ to dissolve the salt, then the clay and silt fraction (an average itized and compared with GIS techniques (see chapter above). of 3.3% of the sample, by weight) was separated by wet-siev­ An older topographic map of the study area (ISTITUTO GEO­ ing. Both the <63 urn and >63 urn size fractions were then GRAFICO MILITARE, 1877), as well as an XVIIIth century ca­ oven-dried at 50°C and weighed. The coarser grain-size frac­ dastral map (VINZONI, 1773), were qualitatively compared tion was sieved mechanically and subdivided into fifteen frac­ but were not utilized for GIS analysis because of their lower tions. Grain-size distributions and statistical parameters degree of accuracy. (mean grain size, median, sorting coefficient, asymmetry co­ Aerial photographs taken in 1950,1981 and 1992 were also efficient) were then calculated for each sample. Only the most qualitatively examined, as well as a large number of non­ relevant results are reported in this paper; the complete data parametric photographs, including postcards. In spite of the set can be obtained from the senior author. low accuracy of these sources of information, they have pro­ vided useful, independent confirmation of the conclusions Mineralogical-Petrographic Composition of the outlined below. Sediment RESULTS As direct measurements of the longshore current at Mon­ terosso Bay are unavailable, the net littoral drift was deter­ Sediment Grain-Size Analysis mined by applying the marked lithologic variability in the Mean sediment grain-size at Monterosso Bay is rather sediment source area. In other words, the rock types cropping coarse (Figure 4), with about 70% of the sample population out in the drainage basin are so distinctively different that comprised between very coarse and medium-grained sand they can be used as natural tracers to unravel the long-term (-1 to 2<1». Areal distribution of mean grain size does not sediment dispersal pattern (i.e., the net littoral drift) within exhibit a longshore gradation. There are two areas charac­ the bay. To this end, twenty outcrop samples were taken terized by relatively finer grained sediment (>3<1». The first within the drainage basin, thin-sectioned, and studied micro­ is located between the marina and the landfill; the second­ scopically to determine their mineralogical and petrographic much larger-is located east and southeast of the landfill. components within the sediments of the bay. Subsequently, twenty-eight beach- and bottom-sediment samples were se­ Mineralogical-Petrographic Composition of the lected, epoxy-impregnated, thin-sectioned, and studied micro­ Sediment scopically using the Gazzi -Dickinson point-counting method (GAZZI, 1966; DICKINSON, 1970), which minimizes the effects The distribution pattern of sediment mineralogical-petro­ of grain size on the petrographic composition of the sediment. graphic compositions over Monterosso Bay shows three large Three-hundred points per sample were counted and assigned areas which broadly match the three outcrop belts outlined to thirty-five categories. Compositional variability over the in the previous section, although with a marked shift toward Monterosso Bay area is so large that such degree of analytical the east tc]. Figures 3 and 5). In the southwestern portion of detail is irrelevant for the conclusions of this study, therefore the study area the detritus is exclusively composed of grains only the basic results are reported here. The entire dataset of sedimentary provenance; the central portion is character­ is available from the senior author. ized by predominant ophiolitic detritus mixed with a minor component of detritus derived from sedimentary rocks; the Analysis of Nature and Density of Marine easternmost sector is characterized by broadly equivalent Phanerogams amounts of sedimentary and ophiolitic detritus (Figure 5). Different types of remote sensing techniques have been em­ Analysis of Densities of Marine Phanerogams ployed to quantify the areal distribution of seagrasses, mostly in order to reduce time and cost (e.g. NORRIS et al., 1997; The areal distributions and densities of P. oceanica and C. PASQUALINI et al., 1998). During this study, it was decided nodosa in the study area (Figure 6A, B) portray P. oceanica instead to determine seagrass distribution at Monterosso Bay as mostly present west of the embankment whereas C. no­ through direct measurement. To this end, several SCUBA dosa is present only east of it. The two species are mutually dives were made in 1995 and 1996. During the dives, obser- exclusive, except for a small area immediately east of the

Journal of Coastal Research, Vol. 16, No.2, 2000 300 Cavazza et al.

north 1\

sample sites PHI classes

beach <0 0+1 1+2 2+3 >3 LIGURIAN SEA samples --.-._.~.-- r------j 0 100 200 300 400 500m

Figure 4. Mean grain size ( scale) of marine and beach sediment samples at Monterosso Bay.

embankment. Widespread remnants of a dead Posidonia INTERPRETATION OF RESULTS matte are present east of the embankment. Physical Parameters The two grain-size minima of the bottom sediment are lo­ Coastline Analysis cated downcurrent from man-made structures, i.e. the marina The integrated study of topographic maps, aerophoto­ and the embankment (Figure 4). It is most likely that the two graphs and a wide collection of non-parametric photographs structures have created shadow zones characterized by lower (mostly postcards) indicates that Monterosso Bay has under­ energy hydrodynamic conditions, thus promoting sedimen­ gone beach erosion since the construction of the embank­ tation of finer grained sediment. The virtual absence of clay ment. Shoreline retreat has been widespread (Figure 7), with in both beach and seafloor sediment samples despite the rel­ the exception of (i) the zone immediately upcurrent of the ative abundance of clay-generating source rocks in the Mon­ embankment, where the area of the beach has increased of terosso Bay drainage basin (Table 1, Figure 3), probably about 8,200 m'' since 1970 (TERRANOVA, 1992), and (ii) the points to the selective removal towards the offshore of the small pocket beach in front of the old town. In the latter zone, finer grain-size fractions by waves and nearshore currents. human modifications have been significant, including the Bottom and beach sediment composition over the bay in­ construction of small jetty at the S. Cristoforo promontory dicates a net littoral drift towards the east. This conclusion (see the progradation of the promontory in Figure 7) and a is also supported by the orientation of megaripples mapped breakwater, built in order to promote sedimentation and thus during SCUBA and ROV (Remotely Operated Vehicle) dives compensate the decreased sediment input following the con­ over much of the Monterosso Bay seafloor at depths reaching struction of the embankment (A. Consonni, pers. comm., - 20 meters. These bedforms have wavelengths ranging be­ 1997). tween 40 and 80 em, are inactive during fairweather condi-

Journal of Coastal Research, Vol. 16, No.2, 2000 Coastal Degradation at Monterosso Bay, NW Italy 301

30"

0+20 20+40 40+60 60+80 >80% LIGURIAN SEA d 1do 2do sdo 4do 50dm Punta ~Mesco

Figure 5. Mineralogical composition of sand-sized marine and beach sediment samples at Monterosso Bay expressed as the ratio between grains derived from sedimentary rocks and the total grains analyzed. Three hundred grains per sample were identified. See Fig.1 for location of samples.

tions, and clearly indicate an overall sediment transport to­ most of the sediment present in the bay, as indicated by the ward the ENE, particularly during major storms. petrographic analysis discussed above. Conversely, beach ero­ The marked increase in the relative percentages of gabbro sion along the eastern, downcurrent half of the bay is the and serpentinite clasts in the sediment samples taken within result of the construction of the embankment which deflects the bay relative to the abundance of the various rock types the longshore current towards the offshore. Evidence of such in the drainage basin (Figure 3, inset) is interpreted as the deflection gathered during SCUBA dives include (i) ripples result of (i) the removal from the nearshore environment of and megaripples indicating SSE-ward sediment movement in the finer grain-size fraction-mostly generated from the ero­ the area directly south of the embankment, and (ii) a hum­ sion of mudrock terrains-due to the high-energy hydrody­ mocky morphology (herbier de colline of Bounotrassouz et namic conditions of Monterosso Bay, and (ii) the more me­ al., 1985) in the Posidonia meadow in the same area. This chanically resistant nature of gabbro and, subordinately, ser­ peculiar morphology is often the result of high-velocity cur­ pentinite grains compared to the mudrock common within rents partially eroding the meadow. the sedimentary terrains of the drainage basin. The retrogradational trend characterizing most of Monter­ Biological Parameters osso Bay is the result of two coexisting but distinct processes. Cliff erosion along the western, upcurrent half of the bay is The present-day areal distribution of marine phanerogams a naturally occurring phenomenon unrelated to human activ­ within Monterosso Bay is likely the result of the progressive ity. Figure 7 shows an average shoreline recession in this westward retreat of an originally larger P. oceanica meadow. area of ca. 15 meters in 41 years, thus pointing to a cliff This view is substantiated by (i) direct underwater observa­ retreat rate of ca. 0.3-0.4 m1yr. This area is the source of tion of the remnants of a dead P. oceanica meadow along the

Journal of Coastal Research, Vol. 16, No.2, 2000 302 Cavazza et al.

no<1h A

25,

30 <,

0+5 5<25 25<50 50+75 .75'" LIGURIAN SEA f---~-- ~------' o 100 200 300 400 500 m

E Promontorio S,Cristoioro north L~

20 -,

25,

30 ......

0+5 5+25 2S+SO 50+75 >75 % LIGURIAN SEA .-- . o 100 200 300 400 500 m

Figure 6. Areal distribution and density of Posidonia oceanica (above) and Cymodocea nodosa (below) meadows at Mont erosso Bay. P. oceanica is mostly present to th e southwest of th e landfill (upcurrent) wher eas C. nodosa is present only downcurrent from it. The distr ibution of C. nodosa mat ches th e grain- size minimum eas t of th e landfill (cf Figure 4).

Journal of Coas ta l Research, Vol. 16, No.2, 2000 Coastal Degradation at Monterosso Bay, NW Italy 303

MONTE E

Corone

1979 SHORELINE

1938 SHORELINE

NET LITTORAL DRIFT

SEDIMENTARY INPUT FROM CLIFFS

SEDIMENTARY INPUT FROM STREAMS (thickness of arrowca. proportional to average waterdischarge) - SHORELINE RETREAT + SHORELINE PROGRADATION

SAND BEACHES

LIGURIAN SEA \ ; : i ; i j o 100 200 300 400 500 m Punta ····,IMesco

Figure 7. Summary of sediment entry points and dispersal pattern at Monterosso Bay; overall progradational and retrogradational trends of coastline are also shown. Coastline position at Monterosso Bay is based on the GIS analysis of topographic maps (lSTITuTO GEOGRAFICO MILITARE, 1938; REGIONE LIGURIA, 1979). See text for discussion.

eastern portion of the bay and (ii) interviews with the local ports further the interpretation of a progressively retreating population pointing to a more extensive Posidonia meadow Posidonia meadow, as C. nodosa is tolerant of a wider range along the eastern portion of the bay prior to the construction of bottom sediment grain sizes. of the embankment. Most likely, the embankment has cre­ ated a low-energy shadow zone on its eastern, downcurrent DISCUSSION AND CONCLUSIONS side, thus promoting finer-grained sedimentation and wors­ ening the health conditions of the Posidonia meadow. The Loss of seagrass-dominated ecosystems worldwide has been meadow has progressively retreated westward and has been attributed to anthropogenic modifications of watersheds, pol­ partially replaced by the more adaptable C. nodosa. In fact, lution, climate change and diseases of global significance. Lo­ C. nodosa is an opportunistic species; like other small-size cal human activities in coastal waters also contribute signif­ taxa of phanerogams it displays the fast rhizome elongation icantly to the destruction of seagrasses: dredging and dump­ rate and leaf turnover necessary to colonize new environ­ ing, bottom trawling for fish and shellfish, recreational boat­ ments (DEN HARTOG, 1977) and to occupy disturbed habitats ing, aquaculture practices, oil spills, and the construction of (DUARTE, 1991), replacing in some cases the more sensitive docks, marinas and causeways (LIVINGSTON, 1984; CLARKE P. oceanica (PERES and PICARD, 1964). The match between and KIRKMAN, 1989; SHORT and WYLLIE-EcHEVERRIA, 1996). the distribution of C. nodosa (Figure 6B) and the sediment As seagrasses also trap and anchor sediments, and dampen grain-size minimum east of the embankment (Figure 4) sup- waves and currents action, their progressive disappearance

Journal of Coastal Research, Vol. 16, No.2, 2000 304 Cavazza et al. is likely to cause an increase in the amount of sediment sus­ Sgorbini (ROV dives); O. Ferretti (grain-size analysis); M. AI­ pended in the water and to enhance erosion of sea bottoms tizio, G. Gabbianelli, L. Giacomelli (digitalization of maps); and shores. F. Gamberini and A. Mordenti (thin-sections preparation); G. Monitoring of P. oceanica beds is being evaluated as a tool Gandolfi and L. Paganelli (petrographic analyses); M. Ligi to test the health of Mediterranean coastal environments and (analysis of coastline change). The following individuals pro­ several countries have developed programs to study the dis­ vided useful data: V. Bo, N. Corradi, R. Lintas, M. Piccazzo tribution and the characteristics of seagrass beds (e.g. BE­ and R. Terranova. Particular thanks go to the mayor ofMon­ NEDITO et al., 1990; BOUDOURESQUE et al., 1990). In recent terosso al Mare, Mr. Antonio Consonni, for his continuous times, P. oceanica meadows showed a dramatic decrease in help throughout this study. areal extent (PEIRANO and BIANCHI, 1995; MARBA et al., 1996) and this seagrass is actually protected by the Barcelona LITERATURE CITED Convention, the U.N.-sponsored treaty aimed at safeguarding BENEDITO, V.; TORRES, J.; GINER, I.-M.; ESTEBAN, J.-L.; CAPAC­ the Mediterranean environment. This has resulted in nu­ CIONI, R., and GARCIA-CARRASCOSA, A.-M., 1990. Distribution and merous biological, biochemical and ecological studies of sea­ preliminary evaluation of the state of the Posidonia oceanica on grass-dominated communities and an increasing awareness the coasts of the Gulf of Valencia (Spain, western Mediterranean). of the role these plants play in the coastal marine environ­ Rapp. Comm. Int. Mer Medit., 32. BIANCHI, C.N. and PEIRANO, A., 1995. Atlante delle Fanerogame ma­ ment. rine della Liguria. ENEA Centro Ricerche Ambiente Marino-La Many studies have reported a decline of seagrass commu­ Spezia, 146p. nities, but relatively few of them have linked these changes BLANC, J.J. AND JEUDY DE GRISSAC, A., 1984. Erosion sous-marine to human activity or natural stress, and very few have com­ des herbier a Posidonia oceanica (Mediterranee), In: BOUDOUR­ ESQUE, C.F.; JEUDY DE GRISSAC, A., and OLIVER, J., (eds.), Inter­ pared seagrass distribution before and after the disturbance national Workshop on Posidonia Oceanic Beds, Marseille, France, event (MEISNEZ et al., 1981; CLARKE and KIRKMAN, 1989; 23-28. SHEPERD et al., 1989; KIRKMAN, 1990). The relations be­ BOUDOURESQUE, C.F.; JEUDY DE GRISSAC, A., and MEINESZ, A., tween physical and biological parameters have been rarely 1985. Un nouveau type d'herbier a Posidonia oceanica: l'herbier taken into account. Monterosso Bay provides a good example de colline. Rapp. Comm. Int. Mer Medit., 29, 173-175. BOUDOURESQUE, C.F. and MEINESZ, A., 1982. Decouverte de of a biological perturbation triggered by a marine coastal con­ l'herbier de posidonie. Pare National de Port Cros, Cahiers, 4, 1­ struction. In this area, the building of the embankment has 80. resulted in the dramatic alteration of the hydrological pat­ BOUDOURESQUE, C.F.; PERGENT, G.; FRANCOUR, P.; HARMELIN­ tern: the longshore current has been deflected toward the off­ VIVIEN, M.; JANGOUX, M.; MAZZELLA, L.; PANAYOTIDIS, P.; PER­ GENT-MARTINI, C.; RAMOS ESPLA, R.; ROMERO, J., and SCIPIONE, shore (Figure 7) and the area downcurrent has become more M.B., 1990. Le COST 647: Posidonia project. Posidonia Newsletter, calm and the site of finer grained sedimentation. These phys­ 3,27-34. ical modifications have forced corresponding variations in the BRIVIO, R., 1996, Aspetti cartografici, fenologici e bionomici di una type, density and health of phanerogams present within the prateria di Cymodocea nodosa. Unpublished Thesis, University of bay. Parma, Italy, 85p. BUIA, M.C.; CANCEMI, G.; PROCACCINI, G., and MAZZELLA, L., 1992. In conclusion, this study demonstrates that physical and Germination and growth of Cymodocea nodosa in different popu­ biological parameters at Monterosso Bay are covariant. In lations. Oebalia, 17, 275-282. this area, biological parameters such as the nature, density CLARKE, S.M. and KIRKMAN, H., 1989. Seagrass dynamics. In: and state of health of marine phanerogams match physical LARKUM, A.W.D., MCCOMB, A.J., and SHEPERD, S.A., (eds.), The Biology ofSeagrasses with Special Reference to the Australian Re­ parameters (bottom sediment grain-size, orientation of long­ gion. Amsterdam, The Netherlands: Elsevier, 304-345. shore current) and have recorded a hydrologic perturbation DEN HARTOG, 1977. Structure, function and classification in sea­ triggered by the construction of an embankment. As sea­ grass communities. In: McRoY, C.P. and HELFFERICH, C., (eds.), grasses are very sensitive to environmental changes, the Seagrass ecosystem: a scientific perspective. New York: Marcel Dek­ mapping of their areal distribution, if properly interpreted, ker, pp. 89-121. DE STEFANIS, A.; MARINI, M.; TERRANOVA, R.; CANEPA, G.; CARLI, can provide significant clues on medium-term coastal dynam­ M.; DE LUIGI, G., and GIORGI, M., 1978. Due esempi di analisi ics and perturbations. The use of such biological mapping geomorfologica di dettaglio sui promontori di Portofino e del Mesco technique in coastal areas, where applicable, should be pref­ sulla costa ligure. Memorie Societe Geologica Italiana, 19, 153­ erably integrated with the determination of physico-chemical 160. DICKINSON, W.R., 1970. Interpreting detrital modes of graywacke environmental parameters (current and wave direction and and arkose. Journal of Sedimentary Petrology, 40, 695-707. velocity, net littoral drift, sediment grain-size, etc.) which DUARTE, C.M., 1991. Allometric scaling of seagrass form and pro­ have been long employed in coastal studies but, alternatively, ductivity. Mar. Ecol. Prog. Ser., 77, 289-300. it could represent on its own a relatively fast, preliminary FIERRO, G.; TUCCI, S.; CAMPI, F.; CORRADI, N.; CORTEMIGLIA, G.C.; assessment of coastal environmental quality and perturba­ FANUCCI, F.; FIRPO, M., and PICCAZZO, M., 1990. Sheet 95-La Spezia. Atlante delle Spiagge Italiane: Consiglio Nazionale delle tions. Ricerche, Rome. GAZZI, P. 1966. Le arenarie del flysch sopracretaceo dell'Appennino ACKNOWLEDGEMENTS modenese; correlazioni con il flysch di Monghidoro. Mineralogica et Petrographica Acta, 12, 69-97. GONGORAGONZALES, E., 1994. Cartografia sedimentol6gica a escala We would like to thank the many people who helped during 1:5000 de una pradera de faner6gamas marinas (Posidonia ocean­ the various stages of this research: C.N. Bianchi (research ica, Cymodocea nodosa): Monterosso al Mare, Italia. Unpublished planning and SCUBA dives); C. Morri (SCUBA dives); S. Masters Thesis, University of Perpignan, France, 34p.

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