Response of the aquatic invertebrate community to the eradication of an exotic invasive fish 30 years after its introduction into an Iberian alpine lake

Abstract

In Lake Grande de Penalara, an originally fishless small high mountain lake in the Central Iberian Peninsula, brook trout (Salvelinus fontinalis) was introduced in the 1970s, and then eradicated 30 years later using gillnets. In this study, we investigated the time-course and changes in macroinvertebrates and zooplankton communities, before and after the eradication, by studying their richness and several biological and ecological traits of macroinvertebrates. Macroinvertebrates richness increased from 13 taxa coexisting with fish, up to a maximum of 27 taxa after the eradication. Rare groups usually affected by fish predation, e.g. swimmers in surface and open waters, showed high dispersal and recolonization capabilities, while those with burrowing, interstitial or crawler habits maintained their presence, and even with the presence of fish given their advantage of hiding from being directly sighted by fish. Taxa with affinities for rare habitats within the lake (e.g. macrophyte beds) occasionally appeared 4–6 years after eradication. In contrast, zooplankton assemblage did not significantly change in richness in the 10 years after eradication. No new species of cladocerans or copepods appeared after fish removal, but 4 new rotifer taxa appeared and 5 disappeared. This was apparently more related to a change in water quality or trophic status as a consequence of the fish removal than to the direct effect of fish removal on rotifers. Zooplankters were significantly smaller, on average, before fish eradication rather than later, indicating that the community responded to the change in predation pressure.