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(IF 0.36; Q3); International audience; The seasonal dynamics of the mollusc fauna associated with intertidal eelgrass Zostera noltei beds on the south-eastern coasts of Tunisia (Central Mediterranean Sea) was studied in relation to water column parameters (temperature, salinity and chlorophyll a), sediment type (grain size, percentage of organic matter) and eelgrass bed descriptors (shoot density, leaf height and width, number of leaves per shoot) at two sites in the Gulf of Gabès. From July 2013 to April 2014, samples were collected (five replicates per season and per site) from bare sediments and eelgrass bed. The 4,886 individuals identified belonged to 82 mollusc species from 42 families. Infaunal bivalves such as Scrobicularia plana, Loripes orbiculatus and Macomangulus tenuis were predominant, while the gastropods Jujubinus striatus, Pirenella conica and Bittium reticulatum dominate in the epifauna. Infaunal and epifaunal abundances were positively correlated with leaf biomass and sediment organic matter content, respectively. Species richness and abundance showed significant seasonal variations, with maxima in spring and summer and minima in autumn and winter, and were positively correlated with phenological changes, temperature, and salinity. Our results support that seasonal dynamics of the mollusc assemblage are mainly linked with the biological cycle (e.g., recruitment events) of certain dominant species.

The Kneiss islands, located in the Gulf of Gabès (Southeastern Tunisia), represent a site of international interest in terms of their ornithological diversity (Important Bird Area, SPAMI and Ramsar Site) and are heavily exploited for clams and fish resources. In an effort to assess the ecological status of the intertidal ecosystem, and to facilitate management and conservation of the resources, an ecological survey of the macrobenthic component was carried out from January to March 2012. This study involved identifying the benthic fauna and assessing the spatial distribution on the southern unperturbed Zostera noltei mudflats by human activities. A total of 102 macrobenthos taxa is identified at 19 stations with a predominance of crustaceans (37%), polychaetes (27%) and molluscs (23%). The AMBI index shows that the area has a good ecological status. Cluster Analysis and Multidimensional scaling identify three benthic assemblages on the basis of their faunal similarity in relation to sediment types and organic matter contents.