Comparative trophodynamics of anchovyEngraulis encrasicolusand sardineSardinops sagaxin the southern Benguela: are species alternations between small pelagic fish trophodynamically mediated?

Abstract The results of detailed morphological, experimental, field and modelling studies on various aspects of the trophic ecology of sardine Sardinops sagax and anchovy Engraulis encrasicolus in the Benguela ecosystem are synthesised, and differences in the trophodynamics of these two species are highlighted. Anchovy possess a relatively coarse branchial apparatus; feed predominantly by particulate-feeding and maximise their net energetic gain by using this feeding mode; show higher weight-standardised clearance rates than do sardine for prey >580μm; are most efficient at assimilating nitrogen from zooplankton and excrete 50% of ingested nitrogen; are able to feed on phytoplankton but derive the bulk of their dietary input from smaller zooplankton; and maximise their scope for growth on microzooplankton. These differences provide compelling evidence that anchovy and sardine are trophically distinct, and indicate that the two species show resource partitioning based on zooplankton size. The implications of these trophic differences for ecosystem functioning are discussed, and support the hypothesis that species alternations between anchovy and sardine, both in the southern Benguela and in other upwelling ecosystems, are likely to be trophodynamically mediated. Keywords: ANCHOVYSARDINESOUTHERN BENGUELASPECIES ALTERNATIONSTROPHODYNAMICS