8th International Conference on Shellfish Restoration October 2–5, 2005 Brest, Brittany, France BIOCENOTIC CHARACTERIZATION AND SHELLFISH ABUNDANCE IN A NATURALLY PRESERVED AREA OF KERKENNAH ISLAND (TUNISIA) Nejla Aloui-Bejaoui *, Slim Gana* and Marcel Le Pennec ** ***Institut National Do not disseminate without Agronomiqueauthor authorization de Tunisie ** UMR ---CNRS-CNRS 6539 LEMAR, IUEM France Geographic location Situation : 11°et 11°20’ East 34°37’ et 34°37’ North Kerkennah Islands : - located at 12 miles far away from Sfax - made of 14 islands - SO – NE direction on 35 km Tunisia Kerkennah - Surface about 150 000 km² Islands Gulf of Gabès Do not disseminate without author authorization Kerkennah includes two principal islands: Gharbi and Chergui Around Kerkennah, the underwater morphology is characterized by the succession of mudholes and sandy bottom with mediterranean seagrasses Posidonia oceanica, Chergui Cymodocea and Caulerpa beds notched by channels which connect mudholes with the open sea Sfax Gharbi In Kerkennah, tide is a Channel significant factor (the higher in Mediterranean sea). Tide Sandy bottoms magnitude varies from 90 cm to 120 cm : currents are more significant in Dothe not disseminate without author authorization channels than in shallow water There is nor industrial activity neither urban concentration in Kerkennah Island Do not disseminate without author authorization In kerkennah, hydrological parameters allow fishermen to practice inshore fishing and to adapt their fishing tackle to these particular conditions. Among others coastal fishing technical used, the fixed fishery or the " cherfia “is a very typical kerkennian fishing tackle Palm’s leaves Nets It is an ancestral fishing technical that ended in the parcelling of the shallow waters in the same way that are divided plots of land. Do not disseminate without author authorization Do not disseminate without author authorization Not a destructive fishing The activity of this harbour is devoted to persons, vehicles and goods transportation from or to the city of Sfax The water inside the basin is affected by a moderated hydrocarbons pollution, due to ships traffic and to its confined location. But this pollution is spatially limited and is not affecting the coastal area outside the port. SFAX Sampling site DoSidi not Youssef disseminate Port without author authorization -2.20 m In order to evaluate the biodiversity level in this area, samples S3 were collected in 10 sites on soft bottoms and on macrobenthos. P Posidonia oceanica C C Cymodocea nodosa Cp Caulerpa prolifera -5.65 m -3 m S6 S1 -1.80 m C-P S7 C-P -4.40 m -1.65 m S10 S2 -2.30 m -2.35 m -0.90 m S9 C-P S4 S5 -1 m C-Cp S8 p C-P-Cp PORT C-P Do not disseminate without author authorization SAMPLING Samples were taken from the 10 sites by scuba diving on 1 m² surface area. Separated samples were taken from the bottom layer and on macroflora/macrofauna. All samples were washed and sieved (mesh size = 2 mm) Macrofauna collected was counted and identified to species level. In order to verify that the area surrounding the Sidi-Youssef harbour is not contaminated by pollutants, we have analysed the concentration of bottom sediments in classical heavy metals, i.e. Cd, Zn, Pb, Cu, As, and Hg in samples collected at all the stations (High frequency Inductively coupled plasma) Do not disseminate without author authorization Statistical analysis -Species richness (number of species) -Abundance -Shannon-Wiener diversity index (H’; log2) considers the species richness and the proportion of each species within the community, with low H’ indicating a low diversity (Hayek and Buzas, 1997) - Pielou’s evenness (J’) - Hierarchical clustering for sites and group was done using group-average linking of Bray-Curtis similarities (Bray and Curtis, 1977; Clark and Warwick, 1994) as well as multi- dimensional scaling (MDS) to show a relative similarity between samples. All univariateDo not disseminate and multivariate without measuresauthor authorization were performed using the PRIMER v5 package (2001). RESULTS Site characteristics during study period 1 2 3 4 5 6 7 8 9 10 Depth (m) 5.65 1.65 2.20 2.30 2.35 3 1.80 1.00 0.90 4.40 Tpt (°C) 17.3 17.7 17.5 17.7 17.4 17.2 17.5 16.2 16.5 16.7 transparency 5.65 1.65 2.20 2.30 2.35 3 1.80 1.00 0.90 1.80 Organic C - - - 2.05 2.77 - - 1.52 1.21 - Mineral C 11.97 8.79 9.59 9.69 9.34 8.99 9.58 10.59 8.82 - Heavy metals 1 2 3 4 5 6 7 8 9 10 Zn 6.1 6.2 2.4 1.6 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Pb <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Cd <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Cu <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 As 4.3 5.3 8.9 6.0 7.5 14.7 10.0 9.6 7.0 4.3 Ba 2.2 45.1 45.8 37.9 550.3 49.2 59.7 43.1 33.8 19.8 Hg <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 The studied area is not chemically contaminated. It is characterized by heavy metals concentration lower than the normal concentration found in coastal area The only notable anthropogenic stress that has concerned the Sidi-Youssef area is related to dredging works conducted for enlarging and for deepening both the Do not disseminate without author authorization entrance channel and the harbour basin. Dredged materials have been deposited and accumulated on both sides of the harbour (along the north and south docks) 100 100 100 50 50 50 0 0 0 -5 0 5 10 -5 0 5 10 -5 0 5 10 Cumulative mass retained(%) Cumulative mass retained(%) Cumulative mass retained(%) Cumulative Particle diameter (phi units) Particle diameter (phi units) Particle diameter (phi units) 100 100 100 50 50 50 0 0 0 -5 0 5 10 -5 0 5 10 -5 0 5 10 Cumulative mass retained(%) Cumulative Cumulative mass retained(%) Cumulative mass retained(%) Cumulative Particle diameter (phi units) Particle diameter (phi units) Particle diameter (phi units) 100 100 100 50 50 50 Do not disseminate without author authorization 0 0 0 -5 0 5 10 -5 0 5 10 -5 0 5 10 Cumulative mass retained(%) Cumulative mass retained(%) Cumulative mass retained(%) Cumulative Particle diameter (phi units) Particle diameter (phi units) Particle diameter (phi units) Textural Group Mean D50 (µµµm): S1 Gravelly Sand Medium Sand 409,1 S2 Gravelly Muddy Sand Fine Sand 184,9 S3 Gravelly Muddy Sand Fine Sand 178,7 S4 Slightly Gravelly Sand Medium Sand 280,4 S5 Slightly Gravelly Muddy Sand Fine Sand 212,1 S6 Slightly Gravelly Muddy Sand Fine Sand 154,5 S7 Gravelly Muddy Sand Fine Sand 185,7 S8 Slightly Gravelly Sand Fine Sand 246,7 S9 Slightly Gravelly Sand Medium Sand 279,2 Do not disseminate without author authorization 78 macrozoobenthic species 34 Mollusca 6 Polychaeta 8 Echinodermata 3 Cnidaria 7 Tunicata 2 Bryozoa 7 Porifera 1 Sipunculida Polyplacophora 6% Scaphopoda 3% Bivalvia 21% Gastropoda 70% Do not disseminate without author authorization Molluscs are present in all sites with different proportions except in stations 1 and 9. Total abundance 100% 80% 60% 37.9% 39.1% 30% 40.9% 46.1% 40% 42.3% 26.7% 22.2% 20% 0% 12345678910 Porifera Cnidaria Polychaeta Sipuncula Mollusca Crustacea Bryozoa Echinodermata Tunicata Do not disseminate without author authorization Group Species Polyplacophora -Lepidochitona cinerea -Chiton olivaceus -Cerithium vulgatum -Haliotis tuberculata -Haliotis lamellosa -Conus mediterraneus -Fissurella sp -Hinia reticulata -Nassa corniculum 24 Gastropods (Cerithium -Calliostoma zizyphinum -Murex trunculus vulgatum the most present) -Gibbula ardens -Aplysia depilans -Gibbula divaricata -Diodora italica -Lunatia pulchella 7 Bivalvia Gastropoda -Monodonta turbinata -Scaphander lignarius -Gibbula varia -Cantharidus striatus 2 Polyplacophors -Nassa reticulata -Gibbula albida -Tricolia pulla -Neverita josephinia -Mitra cornicula 1 Scaphopod. -Hypselodoris elegans Scaphopoda -Dentalium dentalis -Pinna nobilis -Pinctada radiata BivalviaDo not disseminate-Solen marginatus without author authorization -Arca noe -Modiolus barbatus -Modiolus modiolus -Tellina tenuis S2 S6 7% 11% 21% 14% 89% 58% S7 S3 2% 7% 11% 26% 65% 89% Polyplacophora Bivalvia Gastropoda Scaphopoda S8 S4 9% 4% 35% 20% 61% 71% S5 S10 Do7% not disseminate without author authorization 100% 93% Similarity with Echinoderms, Tunicatawith Echinoderms, and Polychaetes (45.5%). Molluscan involving value The highersimilarity got is 100 80 60 40 20 0 Bryozoans Mollusca Tunicata Group Polychaetes Echinoderma Porifera Sipunculida Cnidaria Crustacea Do not disseminate without author authorization Group Cnidaria Crustacea Porifera SipunculidaSipuncula EchinodermaEchinodermata PolychaetesPolychaeta Mollusca Tunicata BryozoansBryozoa Do not disseminate without author authorization Distance d'agrégation 10 20 30 40 50 60 70 80 0 -mixed -mixed - homogeneous - heterogeneous 3 groups linked Pinctata radiata Phallusia fumigata Phallusia mammilata Cerithium vulgatum Serpula vermicularis Botryllus schlosseri Gammarus gammarus Carcinus mediterrane Diadora italica Gibbula divaricata Aplysia depilans Haliotis lamellosa Haliotis tuberculata Hemimycale columella Tethya aurantium Spirastrella cunctat Ircinia variabilis Crambe crambe Dictyota dichotoma Sargassum vulgare Maja squinado Hypselodoris elegans Mitra cornicula Aplydium proliferum Ophiotrix fragilis Schizobrachiella san Acrocnida neapolitan Processa edulis Balanus amphytrite Conus mediterraneus Astropecten spinulos Solen marginatus Distanceseuclidiennes Lepidochitona cinere Asterina gibbosa Méthodede Ward Perinereis cultrifer Gibbula ardens Ophioderma longicaud Pinna nobilis Cystoseira mediterra Golfingia elongatum Oscarella lobularis Plycitor crystallinu Electra posidoniae Arca noe Trophic groups? Orchestia gammarella Chondrilla nucula Capitella capitata Lunatia pulchela Halimeda tuna Ciona intestinalis Dentalium dentalis Nassa corniculum Mercierella enigmati Nereis diversicolor Clavellina lepadifor Murex trunculus Cymodocea nodosa Idotea sp.