A model of copepod population dynamics in the southern Benguela upwelling region

Abstract

A simple population dynamics model was constructed to simulate temporal variability in the biomass of a dominant copepod Calanoides carinatus (Copepoda: Calanoida) along the West Coast region of South Africa. Calanoides carinatus is extensively preyed upon by the commercially important anchovy Engraulis capensis, thus variability in zooplankton production may serve as a useful predictor of variability in anchovy recruitment levels. The model developed here circumvents the need to include a large number of parameters because it uses satellite-derived estimates of chloro- phyll a concentration and sea surface temperature as primary inputs. Abundance estimates necessary to initialize the model are readily obtainable from biannual research cruises. The model successfully simulates observed features of a copepod population's response to pulses of upwelling and is robust with respect to most of its parameters because minor changes in their values result in predictable changes in model output. The model showed greatest sensitivity to parameters that are difficult to determine empirically, such as predator-induced mortality rates. Gaps in our present understanding of the nature and scale of processes affecting copepod egg abundance, survival and viability in the southern Benguela system were identified as the dominant impediment to simulating copepod popu- lation dynamics in the region.