Pigment signatures reveal temporal and regional differences in taxonomic phytoplankton composition off the west coast of Ireland

The composition of phytoplankton assemblages in April, 1998 in Galway Bay and during a summer phytoplankton bloom occurring southwest of Ireland in August, 1998, was characterized by pigments measured by high-performance liquid chromatography. Pigment data reflecting phytoplankton assemblages dominated by diatoms in Galway Bay and dinoflagellates in the southwest of Ireland were compared to phytoplankton cell counts. Significant relationships were found between the fucoxanthin concentrations and the diatom cell numbers (P < O. 0002 r²0. 63) during April, and between fucoxanthin (P < 0.0001 r² 0.79), 19′ hexanoyloxyfucoxanthin (P < 0.0001 r² 0.77) concentrations and Gyrodinium aureolum cell numbers during the summer bloom.