Spatio-temporal variability in fish-induced predation mortality on plankton: A simulation approach using a coupled trophic model of the Benguela ecosystem

Abstract

We investigate the potential predation pressure that would affect plankton communities spatially and seasonally using a coupled model, where fish-induced predation mortality is explicit. In the southern Benguela ecosystem, the fish model OSMOSE is forced by a biogeochemical model providing plankton prey fields. We analyse the resulting potential predation mortality rate on copepods. Spatially, this mortality rate is higher on the South coast (Agulhas bank) than on the West coast (upwelling zone), reflecting a lower plankton concentration compared to food requirement for fish. Temporally, fish-induced predation mortality decreases at the beginning of the upwelling season, due to a rapid increase of plankton concentration combined with a lag in the subsequent increase of fish biomass. Such strong spatio-temporal patterns in fish-induced predation mortality encourage the development of two-ways coupling between fish and plankton models for better representing the dynamics of the southern Benguela food web.