Aquatic Botany 104 (2013) 170–175 Contents lists available at SciVerse ScienceDirect Aquatic Botany journal homepage: www.elsevier.com/locate/aquabot Associated mollusc communities of a Posidonia oceanica meadow in Cap Zebib (off North East Tunisia) Walid Belgacem a,∗ , Habib Langar b,1 , Gerard Pergent c,2 , Oum Kalthoum Ben Hassine a,3 a U.R. de Biologie, Ecologie et Parasitologie des Organismes Aquatiques, Faculté des Sciences de Tunis, Université Tunis El Manar II, 2092, Tunisia b Laboratoire de Biodiversité et Biotechnologies Marines, Institut National des Sciences et Technologies de le Mer, 28, Rue du 2 mars 1934, 2025 Salammbô, Tunisia c Université de Corse, UMR CNRS 6134, Faculté des Sciences et Techniques, BP 52, 20250 Corte, France article info Article history: Received 15 July 2010 Received in revised form 30 May 2011 Accepted 21 September 2011 Available online 14 October 2011 Keywords: Mediterranean Seagrass Mollusc Tunisia abstract Mollusc communities associated with the seagrass Posidonia oceanica were investigated in Cap Zebib (North-Eastern Tunisia). Samples were collected monthly from May 2007 to May 2008, in two stations located at 3 and 12 m depths using a corer of 25 cm diameter. A total of 753 individuals belonging to 47 species were identified. The species richness (S) and Shannon–Wiener diversity index (H ′ ) showed significant variation in relation with depth and sampling period, with higher values at 3 m depth. The community structure at 3 m depth varied considerably from one month to another, while 12 m depth did not show any significant temporal variability. The results of similarity percentage (SIMPER) and Fac- torial Correspondence Analysis (FCA) showed that the species Clanculus cruciatus, Cantharus dorbignyi, Columbella rustica and Cardita calyculata contributed most to the distribution pattern of the mollusc community at 3 m depth. In contrast, at 12 m depth, the highest contributions were given by the species Jujubinus exasperatus, Smaragdia viridis and Tricolia pullus. Taking into consideration a possible relation- ship between the faunal composition and plant (P. oceanica) features, a negative correlation was found between the number of mollusc species, Shannon–Wiener diversity and water depth. In contrast, a pos- itive correlation was noted between the number of species and meadow shoot density, with high values in shallow area and more dense stands. For the abiotic parameters, a positive correlation was observed between Shannon–Wiener diversity and the dissolved oxygen. The Leaf Area Index was also positively correlated with temperature and dissolved oxygen. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The high animal biodiversity recorded in Posidonia oceanica meadows is related to the availability of microhabitats provided by the high spatial complexity of both the plants and the ecosystem that they form (Buia et al., 2000). Specific associations of inver- tebrate fauna with P. oceanica microhabitats formed by the leaf canopy, the rhizome layer and the matte, are well recognized. Considering the relationship between mollusc assemblages and meadow complexity, shoot density and other plant features should affect the structure of the associated fauna assemblage (Scipione et al., 1996). It is well known that features of P. oceanica meadows (e.g. shoot density) and plant biometric parameters (leaf length, width and surface, leaf and epiphyte biomass) show a relatively high ∗ Corresponding author. Tel.: +216 20 337 084; fax: +216 71 871 666. E-mail address: walidbelgacem@yahoo.fr (W. Belgacem). 1 Fax: +216 71 732 622. 2 Fax: +33 04 95 46 24 41. 3 Fax: +216 71 871 666. spatial variability at mesoscale level (Zupo et al., 2006). However, this spatial variability decreases with depth, with the exception of the number of leaves (Gobert et al., 2003). Along the Tunisian coastline, several studies were carried out on the composition and structure of benthic macroinvertebrate communities. The majority of these studies focused on the ben- thic fauna in the Gulfs of Tunis and Gabes and some coastal lagoons (Zaouali, 1993; Ayari and Afli, 2003; Afli et al., 2008; Diawara et al., 2008). However, a few studies were undertaken on macroin- vertebrates associated to P. oceanica meadows, and most of them were restricted to a particular taxon, e.g. amphipods (Zakhama- Sraeib et al., 2005, 2006). What remains to be characterized are the other P. oceanica-associated taxa along the Tunisian coastline – namely molluscs – an important group in marine fauna. Previous work on variations in the composition of the mollusc community due to biogeographic conditions, depth-zonation models and possi- ble annual variations was mainly conducted along the north coasts of the Mediterranean Sea (Russo et al., 1984, 1991a,b; Scipione et al., 1996; Borg et al., 2006). In this work, we hypothesise that mollusc community com- position along the Tunisian coastline are determined by spatial variation in P. oceanica meadow structure. 0304-3770/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.aquabot.2011.09.012