Production of the Copepod Eurytemora affinis in the Bristol Channel

Abstract

A shipboard method for determining development rates of copepods under prevailing conditions of food and temperature in 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 .mu.g dry wt m-3 day-1 in Jan. and May when the numbers of this copepod were, respectively, 1.42 and 4.83 m-3. Population P/B [production/biomass] quotients varied between 0.03 and 0.13 day-1, giving an annual P/B of 33 yr-1. For the later developmental stages, the proportion of animals molting 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; food and predation pressures may influence production more than salinity or estuarine flushing. When compared with published rates for this species fed ad lib 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.