Biodiversity, biogeography and potential trophic impact of Protoperidinium spp. (Dinophyceae) off the southwestern coast of Ireland

This study is the first detailed investigation of the diversity, distribution and potential grazing impacts of Protoperidinium spp. in relation to the hydrography and phytoplankton distributions off the southwestern coast of Ireland. In late July 2003, the area was well stratified, and the Irish Shelf Front was apparent as a strong salinity front offshore. Thirty-two species of Protoperidinium were identified and classified as nearshore, offshore and widespread, based on distribution. In the Celtic Sea, phototrophic dinoflagellates dominated the plankton community nearshore, whereas diatoms dominated offshore of the Irish Shelf Front. Protoperidinium species, including P. steinii, P. depressum and the putative azaspiracid-toxin producer, P. crassipes, were most abundant nearshore in the Celtic Sea. The Bantry Bay section had the highest concentration and diversity of plankton in the study area. Most Protoperidinium species had the highest abundance nearshore along the Bantry Bay section, but the highest concentration of P. crassipes was offshore. Given the plankton concentrations and estimated grazing rates of Protoperidinium species, Protoperidinium had the potential to consume 30–80% of the dinoflagellate or diatom standing stock at the time of the study.