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 ). Tide Sandy bottoms magnitude varies from 90 cm to 120 cm : currents are more significant in Do the 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 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 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 - sp -Hinia reticulata -Nassa corniculum 24 Gastropods (Cerithium -Calliostoma zizyphinum -Murex trunculus vulgatum the most present) -Gibbula ardens -Aplysia depilans -Gibbula divaricata - italica -Lunatia pulchella 7 Bivalvia -Monodonta turbinata -Scaphander lignarius -Gibbula varia -Cantharidus striatus 2 Polyplacophors -Nassa reticulata -Gibbula albida -Tricolia pulla - 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, Tunicata and Polychaetes (45.5%). (45.5%). Polychaetes and Echinoderms,with Tunicata is got The highersimilarity value involving Molluscan 100 80 60 40 20 0 Do not disseminate without author authorization

Bryozoans

Mollusca

Tunicata Group

Polychaetes

Echinoderma

Porifera

Sipunculida

Cnidaria

Crustacea Group

Cnidaria

Crustacea Porifera SipunculidaSipuncula

EchinodermaEchinodermata PolychaetesPolychaeta Mollusca

Tunicata BryozoansBryozoa

Do not disseminate without author authorization Méthode de Ward Distances euclidiennes

80

70

60

50

40

30

20

Distance d'agrégation Distance 10

0 Arcanoe Idotea sp. Idotea Tricoliapulla Pinna nobilis Pinna Tellinatenuis Fissurellasp. Gibbulavaria Actiniaequina Diadora italicaDiadora Gibbulaalbida Halimeda tuna Halimeda Maja squinado Maja Mitracornicula Hiniareticulata Gibbulaardens Talitrussaltator Irciniavariabilis Ophiuratextura Pinctata radiata Pinctata Processaedulis Murextrunculus Crambe crambe Crambe Ophiotrixfragilis Nassareticulata Aplysiadepilans Lunatia pulchela Lunatia Chiton olivaceus Chiton Asterinagibbosa Ciona intestinalis Ciona Capitellacapitata Chondrillanucula Tethya aurantium Tethya Solen marginatus Solen Haliotislamellosa Caulerpa prolifera Caulerpa Nassacorniculum Anemonia sulcata Anemonia Gibbuladivaricata Holothuriaforskali Plycitorcrystallinu Perinereiscultrifer Modiolusbarbatus Phallusiafumigata Dentalium dentalis Dentalium Nereisdiversicolor Oscarellalobularis Electraposidoniae Modiolusmodiolus Clavellinalepadifor Spirastrellacunctat Dictyotadichotoma Haliotistuberculata Neveritajosephinia Balanus amphytrite Balanus Botryllusschlosseri Sargassum vulgare Sargassum Cerithiumvulgatum Holothuriatubulosa Posidonia oceanicaPosidonia Aplydiumproliferum Golfingiaelongatum nodosa Cymodocea Cantharidus striatusCantharidus Mercierellaenigmati

Serpula vermicularis Serpula Calliostomazizyphin Monodonta turbinata Monodonta Schizobrachiellasan Cystoseiramediterra Lepidochitona cinere Lepidochitona Phallusiamammilata Astropecten spinulos Astropecten Alcyoniumpalmatum Acrocnidaneapolitan Sphaeroma serratum Sphaeroma Scaphander lignarius Scaphander Carcinusmediterrane mediterraneus Conus Hypselodoriselegans Eupolymnia nebulosa Eupolymnia

Orchestiagammarella Gammarus gammarus Gammarus Hemimycalecolumella Ophioderma longicaud Ophioderma Gammarus aequicauda Gammarus 3 groups linked authorization author without disseminate not Do Trophic groups? - heterogeneous - homogeneous -mixed Abundance Species Richness

120 50 100 40 80 30 60 20 40 20 10 0 0 S1 S10 S2 S3 S4 S5 S6 S7 S8 S9

High species richness and abundance for sites 2-3- 4 and in mean level for sites 6-7-8

Do not disseminate without author authorization E Evenness H' Shannon-Wiener diversity

S9 S8 S7 S6 S5 S4 S3 S2 S10 S1

0 1 2 3 4 5

-Diversity and evenness are higher at sites where seagrasses Posidonia oceanica (stations 2, 4, 5, 6, 7, 8) and Cymodocea nodosa (station 3) show a high density. -In the fifth site, mollusks play a great part in a relative strong biodiversity.Do not disseminate without author authorization Species

0

20

40

60 Similarity

80

100 1 9 5 6 7 8 4 2 3 10

At level similarity of 20 %, the cluster show 3 site groups (group 1 : s 5,10 ; groupe 2 : s 6, 7, 8) ; groupe 3 : s 2, 3, 4 . Higher levels of similarity involving Mollusks are obtained in those last sites were seagrasses are present. The higher value of similarity is got for sites 2-3 (50.75%) and 7-8 (46.17%).Do not disseminate without author authorization Species

9 Stress 0.05 8 8 77- 6- 6

4 5 2-3-24 3

10 1

MDS

Sites 1 and 9 : independant : out of harbour and chanel Sites 5 and 10 : low species richness and Gastropod dominance

Group 2-3-4 (toward open sea) and 6-7-8 (harbour) : highest species richness. Predominance of Tunicata for the first group ( Ciona, Phallusia, Clavellina..) and Bivalvia for the secondDo one not (disseminatePinctada radiata without) author authorization 2-3-4 P. nobilis

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7-8 P.radiata Highest value Species richness and abundance : S4, meadow of the Mediterranean seagrass Posidonia oceanica.

This meadow is among ecosystems with the highest productivity and population density

Do not disseminate without author authorization The dense and submerged vegetation provides a settling surface for -epiphytic flora and fauna -Is a structural habitat for many mobile organisms

Do not disseminate without author authorization and submerged vegetation provides a settling surface for flora and fauna a structural habitat for many mobile organisms

Do not disseminate without author authorization The dense and submerged vegetation provides a settling surface for -epiphytic flora and fauna -Is a structural habitat for many mobile organisms

Do not disseminate without author authorization The high species richness is strongly influenced by shellfish essentially in Phanerogams beds.

The favorable medium parameters allow a high productivity and population density in this naturally protected area. Only the port and channel influence the Mollusk presence (sites 1, 9). In all the others stations, mollusk population are present

However, we can notice the installation of invasive species in this area wich can strongly disturb the living of autochtone Mollusk species, essentially the protected bivalvia Pinna nobilis.

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