The algal flora of a subtidal Zostera bed in Ventry Bay, southwest Ireland

Abstract Ventry Bay in County Kerry, southwest Ireland, was surveyed in June 1977 to a depth of 17 m using SCUBA and a grid of stations which were 400 m apart. The principal substrate was sand. Zostera marina L. was dominant and widespread from 0.5 to 13 m below Chart Datum and is the deepest-growing Zostera in Northwest Europe. Sixty species of algae were found and their occurrence and that of Zostera marina was subjected to cluster analysis resulting in one distinct cluster of Zostera marina, Ulva lactuca L., Gracilaria verrucosa (Huds.) Papenf., Polysiphonia elongata (Huds.) Spreng., Ectocarpus sp., Ceramium rubrum (Huds.) C. Ag. and Brongniartella byssoides (Good. et Woodw.) Schmitz. These algae are so common and widespread in the subtidal zone that their co-occurrence with Zostera is not considered to be significant. Zostera occurs virtually as monospecific stands in sand and the co-occurrence of any macroalgae is largely fortuitous and dependent on the heterogeneity of the substrate.