LIFE-HISTORIES OF NEOMYSIS INTEGER, AND ITS COPEPOD PREY, EURYTEMORA-AFFINIS, IN A EUTROPHIC AND BRACKISH SHALLOW LAKE

Data was collected on the population structure and fecundity of the mysid Neomysis integer and the calanoid copepod Eurytemora affinis in Hickling Broad, a shallow and eutrophic brackish lake, over a two-year period 1988/89. Standing biomass and production rate estimates were made using estimates of size-specific dry weights and development times obtained from laboratory measurements, field observations and information found in the literature. Both mysid and copepod are capable of a rapid response to favourable conditions and have high rates of birth, growth and production. E. affinis reproduces throughout the year with an estimated annual (May 1988-May 1989) production of 20 g dry wt m(-2). Copepod standing biomass was less in 1989 compared with 1988 owing to an overall reduction in copepod body-size and a reduction of size at maturity. There was a suggestion from the data that this was caused by predation from a greater number of large (>9 mm body-length) mysids in 1989 compared with 1988. N. integer is highly seasonal in its growth with distinct peaks of recruitment in May and July. Annual (May 1988-May 1989) production of the mysid was estimated as 5.8 g dry wt m(-2). Although E. affinis is the only available prey of N. integer in the lake, the mysid population appears independent of changes in that of the copepod and probably avoids negative predator-prey feedback mechanisms owing to an ability to feed on epiphytic algae.