Daily fecundity of Temora longicornis (Copepoda calanoida) in the Oosterschelde estuary (SW Netherlands)

Daily fecundity of Temora longicornis in the Oosterschelde was estimated in 1986 and 1987 after 24 h incubation of female copepods collected in the estuary. Daily egg production fluctuated between 3 and 25 eggs per female.Egg production rates increased with temperature in the range of 3 to 15°C when algal food was present in excess. Limiting food conditions were found at the end of the phytoplankton spring bloom and occasionally in summer at concentrations of ⩽2 μg chlorophyll·dm⁻³. When chlorophyll maxima were found, predominantly consisting of Phaeocystis, daily fecundity of Temora was suppressed. It could increase, however, in Phaeocystis blooms mixed with diatoms (Rhizosolenia delicatula).Standing stocks of eggs in the springs of 1986 and 1987 were calculated on the basis of the established temperature/fecundity relation and compared with observed numbers, both in the years 1986 and 1987 (estuary provided with a storm-surge barrier in the mouth) and in the years 1983 and 1984 (open estuary).Smaller differences between observed and calculated egg numbers in 1986 and 1987 could be ascribed to possible errors in calculated egg development time and to the different age structure of females in the course of time.Much larger differences were found between the years 1986–1987 and 1983–1984. These are discussed in relation to the following phenomena: sinking of eggs, cannibalism, predation, food quantity and availability, density-dependent effects, hydrodynamical changes of the estuary. Arguments are given for density-dependent factors being responsible for the strongly reduced egg numbers in 1984.