Lower biodiversity of native fish but only marginally altered plankton biomass in tropical lakes hosting introduced piscivorous Cichla cf. ocellaris

Abstract

We compared the species richness and abundance of fish, zooplankton and phytoplankton in nine mesotrophic coastal shallow lakes (Northeastern Brazil) with and without the exotic predator cichlid tucunare or ‘peacock bass’ (Cichla cf. ocellaris). We hypothesized that the introduction of tucunare would lead to decreased abundance and species diversity of native fish assemblages and cause indirect effects on the abundance and species diversity of the existing communities of zooplankton and phytoplankton and on water transparency. Our hypotheses were only partly confirmed. Although fish richness and diversity were, in fact, drastically lower in the lakes hosting tucunare, no significant differences were traced in total fish catch per unit of effort, zooplankton and phytoplankton biomass, plankton diversity or the zooplankton:phytoplankton biomass (TZOO:TPHYTO) ratio. However, zooplankton biomass and TZOO:TPHYTO tended to be higher and the phytoplankton biomass lower in lakes with tucunare. Our analyses therefore suggest that the introduction of tucunare had marked effect on the fish community structure and diversity in these shallow lakes, but only modest cascading effects on zooplankton and phytoplankton.