SEASONAL AND ANNUAL VARIATIONS IN ABUNDANCE AND SPECIES COMPOSITION OF FISH AND MACROCRUSTACEAN COMMUNITIES ON A SCOTTISH SANDY BEACH

Forty-three species of fishes and 16 species of larger crustaceans wer e caught by trawl and seine during a 4 yr study on a sandy beach on th e west coast of Scotland. There were considerable differences in the s pecies composition of the trawl and seine catches such that neither al one provided an adequate description of the sampled community. Approxi mately monthly sampling demonstrated a clear seasonal cycle in abundan ce and species composition. A few species were resident on the beach a ll year round; the majority were only present from spring to autumn. I ncreases in both numbers and species were caused mainly by the recruit ment of young of the year individuals whose numbers subsequently decli ned rapidly probably due to a combination of predation and emigration. There were marked differences in both species composition and abundan ce between years. Annual cycles in species richness and abundance clos ely paralleled those of temperature and salinity. It is suggested that the cycles result mainly from recruitment and mortality rather than f rom immigration and emigration in response to physical factors.