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

Contamination and depuration of Paralytic Shellfish Poisoning by Acanthocardia tuberculata cockles and Callista chione clams in Moroccan waters

International audienceThis study of Gymnodinium catenatum was conducted across two sampling stations; M'diq bay and Oued Laou estuary during the period from July 2007 to May 2009. Gymnodinium catenatum blooms occurred after a rainfall event in autumn and early winter. Statically analyses showed a positive correlation with rainfall. During January 2008, the G. catenatum bloom resulted in contamination of tuberculate cockles and sweet clam by Paralytic Shellfish Poisoning (PSP) toxins. In the Oued Laou estuary, the levels of these toxins in shellfish went beyond the normative threshold for consumption of shellfish, (80 µg SXTeq. /100g of meat) and reached (710 ± 82.07) and (198 ± 6.56) µg SXTeq. /100g of meat in cockles and sweet clam respectively. In M'diq bay, concentrations of PSP toxins in the meat of these two shellfish were lower (256.57 ± 12.22 µg SXTeq. /100g and 80.66 ± 8.14 µg SXTeq. /100g of meat in tuberculate cockles and sweet clam respectively. An experimental test of depuration of tuberculate cockles and sweet clam contaminated by the PSP toxins was conducted in laboratory conditions in the first week of January 2008. The results showed partial and progressive elimination of PSP toxins in two shellfish species over time. In the tuberculate cockle, the elimination of PSP appears to be slower compared with the sweet clam; it took 120 days to reach levels of 80 µg SXTeq. /100g of meat, on the other hand only 3 days were needed to reach this safe concentration in the sweet clam