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 were caught by trawl and seine during a 4 yr study on a sandy beach on the west coast of Scotland. There were considerable differences in the species composition of the trawl and seine catches such that neither alone provided an adequate description of the sampled community. Approximately monthly sampling demonstrated a clear seasonal cycle in abundance and species composition. A few species were resident on the beach all year round; the majority were only present from spring to autumn. Increases in both numbers and species were caused mainly by the recruitment of young of the year individuals whose numbers subsequently declined rapidly probably due to a combination of predation and emigration. There were marked differences in both species composition and abundance between years. Annual cycles in species richness and abundance closely paralleled those of temperature and salinity. It is suggested that the cycles result mainly from recruitment and mortality rather than from immigration and emigration in response to physical factors.