Impact of non-native fish on macroinvertebrate communities of insular tropical small standing waters

While the effect of non-native species on insular tropical ecosystems is relatively well known, their impacts on small standing waters (SSWs) remain understudied. We analysed the impact of introduced fish on invertebrate composition and structure in 24 SSWs on the Guadeloupe archipelago. Two stocking regimes were examined, one with Poeciliidae alone, the other with Poeciliidae in association with Tilapia. Three hypotheses were tested: non-native fish (1) alter the composition and structure of invertebrate communities; (2) modify SSW trophic structure; and (3) affect higher levels of functioning through the potential reduction of invertebrate aerial dispersal. While the impact of Poeciliidae on invertebrate community structure was weak, its effect on community composition was strong, with densities of Hemiptera, Odonata and Coleoptera more than ten times lower in SSWs with Poeciliidae compared with fishless SSWs. The relative densities of both macro- and microinvertebrate predators decreased, whereas those of microphyte-feeders increased, suggesting both top-down and bottom-up effects. Tilapia, when associated with Poeciliidae, tended to mitigate these impacts. At higher function levels, the relative density of invertebrates capable of aerial dispersal decreased in SSWs with Poeciliidae, suggesting a systemic impact on the resilience of SSWs and the trophic web of surrounding ecosystems.