Production of the Copepod Eurytemora affinis in the Bristol Channel

A shipboard method for determining development rates of copepods under prevailing conditions of food and temperature i n situ is described. Abundance and development rates of Eurytemora affinis were determined at a site towards the seaward edge of its range in the Bristol Channel during 3 seasons of the year. Production of E. affinis varied between 0.05 and 0.61 pg dry weight m-3 d-' in January and May when the numbers of this copepod were, respectively, 1.42 and 4.83 rnJ. Population P/B quotients varied between 0.03 and 0.13 d-' giving a n annual P/B of 33 yr-l. For the later developmental stages, the proportion of animals moulting daily varied between 4 % and 33 %, depending on stage and season. The results are discussed In relation to the factors influencing population production at this site in the estuary; it is suggested that food and predation pressures may influence production more than salinity or estuarine flushing. When compared with published rates for this species fed ad-libiturn on algae in the laboratory, development rates of E. affinis in the field were only 10 %-82 %, suggesting that extrapolation of laboratory results to the field to estimated production should only be carried out with care.