Abstract
The phytoplankton of a sheltered inlet of Galway Bay on the west coast of Ireland was investigated in the winter and early summer of 1971 and was found to be limited both in species and numbers. The diatom flora, of just over 70 species, was neritic in character and changed from a Thalassiosira/Skeletonema flora in winter to a Cerataulina flora in early May before reverting to a Skeletonema flora later in the month. The dinoflagellate flora of 15 species was largely oceanic and became prominent only in summer. An annotated list is given with temperature and salinity range for each species. Size reduction in many of the diatoms indicates that the inlet has a closed community. The origins of the flora are mainly boreal but Rhizosolenia hebetata var. semispina (Hensen) Gran is an abundant species in winter. This, together with the presence of temperate oceanic species, indicates that the offshore flora is derived from more than one water body.