Local and external components of the summertime plankton community in Lough Hyne, Ireland a stratified marine inlet

Water samples were collected intensively during summer to study the processes affecting the plankton community in Lough Hyne, Ireland. Multivariate analysis of species counts demonstrated a clear separation between lough samples and water taken from incoming tides. Differences between the lough and adjacent water reflected the strong stratification within the lough. The dinoflagellates Gonyaulax verior, Ceratium furca, Ceratium fusus, Prorocentrum micans and Protoperidinium steinii and the silicoflagellate Dictyocha speculum were all significantly more abundant in the lough than in tidal inflow. The diatoms Thalassionema nitzshioides and Cylindrotheca closterium as well as copepods, nauplii and tintinnids were also more abundant in lough samples. Only Rhizosolenia hebetata, Gymnodinium spp. and Striatella unipunctata had significantly higher average adundances in tidal inflow than in lough samples. However, the average counts of these species were an order of magnitude smaller than the average counts for the most abundant dinoflagellates within the lough. Instead of reflecting the species composition of the adjacent coastal waters, the phytoplankton community in the lough is closer to the situation observed on the stratified side of fronts in the Celtic Sea. There are enhanced populations of dinoflagellates and cell counts of these species tend to increase following spring tides.