A comparison of the ecological effects of two invasive poeciliids and two native fishes : a mesocosm approach

Invasive poeciliid fishes have been negatively affecting recipient ecosystems globally. However, the ecological consequences of their invasions can vary seasonally and spatially, and according to species, limiting our ability to predict their effects. It is also unclear how their impacts differ from those of native fishes. We compared the effects of the invasive mosquitofish (Gambusia affinis) and guppy (Poecilia reticulata) with those of the similar-sized native rice fish (Oryzias curvinotus) and half-banded barb (Puntius semifasciolatus) on invertebrate assemblages, primary-producer biomass, and nitrogen loadings in mesocosms during the wet and dry seasons in tropical Hong Kong. Invasive poeciliids and native fishes reduced invertebrate abundance and richness, and altered assemblage composition, but had no effects on algal biomass or nitrogen loadings. These outcomes were consistent between seasons, although the guppy effects on invertebrates were weaker in the cool dry season. The mosquitofish and the half-banded barb had the strongest influence on invertebrates, followed by the guppy, while rice fish had the smallest effects. This study adds to the scant knowledge of poeciliid invasions in tropical Asia. It reveals that invasives do not always have stronger impacts than native counterparts, and that invasive poeciliids differed in the intensity of their ecological effects.