Trophic role of small pelagic fishes in a tropical upwelling ecosystem

On the basis of an Ecopath model and Ecosim model simulations, the trophic role of small pelagic fish in the Gulf of Salamanca, a tropical upwelling ecosystem on the Caribbean coast of Colombia, was explored using a combination of fishing vulnerabilities and harvest scenarios. Dynamic simulated changes in the biomass of small pelagic fish caused reallocation of the biomass of higher trophic-level organisms but not of lower trophic-level organisms (plankton). This was attributed to bottom-up control exerted by small pelagic fish on pelagic predatory fish, the highest trophic-level predators with a diverse diet trough which consequences of changes in small pelagic fish biomass propagate. Plankton biomass remained almost unchanged, although plankton is the main food of small pelagic fish. Overall, the results indicate that small pelagic fish play an important role in this ecosystem because perturbations of their biomass (brought about by fishing) propagate through the upper part of the system. However, they have little effect on the lower trophic-level groups. By extension, the postulated crucial “wasp-waist” role of intermediate trophic levels occupied by small pelagic fish in temperate and subtropical most productive upwelling regions may not have a full equivalent in tropical less productive upwelling areas.