Short-term variability during an anchor station study in the southern Benguela upwelling system: Fecundity estimates of the dominant copepod, Calanoides carinatus

Abstract

Fecundity studies by indirect (Egg Ratio) and direct (bottle incubation) methods showed that egg production by Calanoides carinatus, downstream of a major upwelling centre, was closely coupled to hydrologically-mediated fluctuations in food availability. Fecundity estimates derived using the Egg Ratio method were lower than those from the incubation method, which we attribute to advection of egg-laden surface layers during upwelling. Improvements in understanding the fecundity-food relationship were achieved by considering phytoplankton size (cells >10 μm), species composition and state of bloom development. Egg production was high (41.6 eggs female −1d −1) during a prolonged quiescent period while a monospecific bloom of Coscinodiscus gigas persisted, but it declined rapidly (5.4 eggs female −1d −1) on the bloom's senescence and its replacement by a surface microflagellate-dominated community. Resumption of egg production occurred with the advection of recently upwelled water supporting a healthy small diatom population. We suggest that the rapid response displayed by female C. carinatus to a pulsed and unpredictable food supply, combined with the capacity to store large lipid reserves, allows this species to successfully exploit upwelling regions.