Seasonal Changes in Density, Composition and Reproductive Biology of Crustacean Populations in the Severn Estuary

Abstract

Changes in the abundance and composition of crustacean populations in the plankton of the Severn Estuary (England) were followed for 25 consecutive months (1973-1975). The collections were made primarily near shore from the cooling intake of the Oldbury nuclear power station. Neomysis integer overwintered at comparatively low densities with all specimens measuring more than 5 mm in length. Inshore swarms of this species were detected early in the summer and most females carried either eggs or embryos. Praunus flexuosus invariably occurred less frequently than N. integer. During the summer, inshore aggregations of adults were probably formed and, although large numbers of berried females were observed at this time, the release of young possibly never occurred in the Oldbury region. Eurytemora affinis was observed only during periods of low salinity in winter with maximum reproductive activity taking place in December. The highest density of Eurydice pulchra occurred early in the summer due to the recruitment of young while, at other times, this species remained comparatively rare. The same pattern was observed in Gammarus salinus but since only a few females carried eggs at any one time reproduction must take place outside of the study area. Crangon crangon maintained greatest numbers during the summer and fall, being almost absent during part of the winter. The growth rate, size at maturity and period of reproductive activity of this species differed from earlier accounts on Severn populations.