Seasonal fluctuations in vertical distribution and breeding activity of a subtidal harpacticoid community in the southern bight,North sea

Seasonal changes in vertical distribution and breeding activity of 14 dominant harpacticoid species from a sandy station in the Southern Bight of the North Sea are described over a period of 1 year, from January 1983 to January 1984.It is clear that the bulk of the meiofauna penetrates deeper than expected from the literature. The need for long cores for quantitative work in subtidal sandy areas is stressed.The factors affecting vertical distribution in the sediment are discussed. Except for the winter breeder Interleptomesochra eulittoralis, all other species bred at least partially in summer when temperature is high. In these species migratory behaviour and reproductive activity were interrelated, and as a result egg development took place in the surface layers of the sand.Only Microarthridion littorale bred continuously throughout the year. In all other species the breeding season, as defined by the simultaneous presence of juveniles and ovigerous females in the population, was either restricted or protracted: distinct maxima occurred at different times in different species, but the majority reached maximum breeding activity in the summer.The observed breeding patterns of the dominant species are compared with those reported from other localities. Most of them are so-called “plastic species”, which show a latitudinally related alteration in breeding periodicity.