Dynamics of Pseudo-nitzschia spp. and domoic acid production in a macrotidal ecosystem of the Eastern English Channel (Normandy, France)

Temporal variations in the Pseudo-nitzschia assemblage were characterized in the Baie des Veys (Normandy, France) from July 2007 to July 2008. This study describes the succession of Pseudo-nitzschia species. Six species were identified, Pseudo-nitzschia americana, P. australis, P. delicatissima, P. fraudulenta, P. multistriata, and P. pungens and their occurrences were related to physical, chemical and biological factors. Pseudo-nitzschia spp. were observed during the whole year, the higher abundance (38.103 cell L-1) and diversity were found in September while the lowest (0.9.103 cell L-1) were observed from October to the end of February. P. americana and P. australis were only seen in September and were positively correlated with high chlorophyll a, temperature and Si(OH)4 concentrations. P. delicatissima and P. fraudulenta were more abundant under high NO3 and low Si(OH)4 concentrations and associated with low chlorophyll a concentrations. P. multistriata appeared in October and in November 2007 and its abundance was correlated with NH4 while P. pungens abundance was not related to any environmental factors tested suggesting high acclimation capacities. In September 2007, P. australis was observed and domoic acid (7.1 ng DA L-1) was measured in the phytoplankton samples. During this period, the phytoplankton population was mostly limited by PO4 and NO3 concentrations. On 17 September a heavy rainfall (15.6 mm) affected the nutrient stocks resulting in Si(OH)4 and NO3 limitations. Our results suggest that this Si(OH)4 limitation might have promoted the production of domoic acid by P. australis. This study presents the first results on Pseudo-nitzschia successions and particulate domoic acid concentrations on the French coasts. This work especially highlights the beginning of autumn as a potential risk period for ASP events linked to P. australis development in the Baie de Seine.