Reduction in fecundity and lipids of the copepod Calanus australis (Brodskii) by strongly pulsed upwelling

Abstract

Gravid female Calanus australis (Brodskii) were starved for varying periods in the laboratory to test the hypothesis that the relatively low Zooplankton biomass in the southern Benguela is caused by a discontinuous, albeit rich, food supply. Egg-production rates and lipid content were monitored for groups of copepods which were starved, fed subsequent to starvation and fed continuously. Average egg production for unstarved females was 27.6 eggs-day −1. Starvation was found to inhibit egg production after 24 h. Cumulative egg production during 5 days of feeding was significantly reduced if starvation was experienced immediately before feeding, being even lower for extended lengths of starvation. The total lipid content of ≈ 17 % of dry mass was reduced to < 4 % following starvation for 9 days. Given a mean dry mass of 184.4 μg, this animal expends 6.4 μg lipid · day −1. It would appear that fecundity is related not only to feeding rate as has been demonstrated but to feeding history also. Phytoplankton blooms in the southern Benguela, usually lasting only 5 days, are interrupted by advection of chlorophyll-free upwelled water. These results support the hypothesis that, although on average food is abundant, starvation experienced during episodic upwelling events may retard the establishment of a large herbivore community.