Temporal and spatial variation of the molluscan community structure in Oualidia Lagoon, Moroccan Atlantic coast

The molluscan assemblages inhabiting the coastal waters of Oualidia Lagoon, Morocco, were studied during winter and summer of 2013. The taxonomic composition and diversity were determined at 43 sample sites. Thirty-four mollusc taxa were recorded in total, including 12 species of bivalves, 20 species of gastropods, 1 species of polyplacophoran and 1 species of cephalopod. Twenty-six of these species are reported here for the first time in Oualidia Lagoon. The gastropod Peringia ulvae and the bivalve Abra alba were the most abundant taxa in both seasons. The deposit-feeder trophic group was highly dominant in both seasons. A classification analysis revealed the existence of three main clusters from downstream to upstream in both seasons: a marine assemblage, a transition assemblage and a lagoon assemblage. Canonical correspondence analyses indicated that the main environmental variables governing the spatial distribution of the molluscs in winter are salinity, temperature and granulometry, whereas in summer they are salinity and granulometry. This study provides a good baseline for future ecological research.