Seasonal variation in Pseudo-nitzschia spp. and domoic acid in the Western English Channel

The seasonal and intra-annual variation of Pseudo-nitzschia species and domoic acid (DA) concentrations, at a long term monitoring site (L4) in the Western English Channel, is reported over an annual cycle (January to December 2009). To determine what drives Pseudo-nitzschia spp. occurrence and DA production at L4 we relate results to a range of physical and chemical environmental parameters. Pseudo-nitzschia spp. occurred throughout the year ranging from 40 cells L−1 and 250×103 cells L−1 with two peaks in abundance occurring in June/July and in August. In August Pseudo-nitzschia spp. accounted for 100% of the total diatom community. Three distinct groups or categories of species were enumerated according to morphology and size; those resembling Pseudo-nitzschia delicatissima cell types, those resembling Pseudo-nitzschia seriata, and those resembling Pseudo-nitzschia pungens/multiseries. The P. delicatissima-group was responsible for the high abundance in August. BEST analysis showed that the three groups were ecologically different with a number of environmental parameters influencing the abundance of the groups. The P. delicatissima-group was significantly influenced by the physical environmental factors of temperature, hours of light, rainfall, as well as phosphate, and salinity, whereas P. pungens/multiseries-group were significantly influenced by macronutrients. The P. seriata-group was significantly influenced by temperature and nitrate. DA was detected over a five week period from May to July with a maximum in June (0.4 ng DA L−1). When DA was present the surface waters were limited by silicate and nitrate. DA was significantly correlated with the presence of the P. seriata-group and the P. pungens/multiseries-group (p<0.05). This is the first time that DA has been detected at the long term monitoring site in the Western English Channel and results suggest that for this site silicate plays an important role in its production.

► We examine Pseudo-nitzschia spp., environmental parameters, and domoic acid (DA) in the Western English Channel.
► Three Pseudo-nitzschia groups were monitored and found to be influenced by different environmental parameters.
► This is the first time that DA has been detected at the long term monitoring site in the Western English Channel.
► DA production likely by Pseudo-nitzschia seriata-types.
► Silicate plays an important role in the production of DA at L4.