Fish assemblage structure in urban streams of Puerto Rico: the importance of reach- and catchment-scale abiotic factors

Abstract

Channelization and urbanization are anthropogenic alterations that act on the reach- and catchment-scale, respectively, to degrade stream habitats. As urban areas continue to expand in the tropics the number of channelized streams will likely increase as well. We examined in-stream habitat and fish assemblage structure in stream reaches with a range of channel alterations and sub-catchment urban land use in the Rio Piedras watershed, Puerto Rico. Nine reaches were surveyed and classified into three categories: unaltered channels (natural), channels that had been straightened and may have reinforced banks (intermediate), or channels where the bank and bottom was replaced with concrete (concrete-channelized). Fishes were sampled using triple-pass electrofishing and relevant reach- and catchment-scale abiotic environmental variables were measured for each site. Fish assemblage structure in the Rio Piedras appears to be influenced by both reach- and catchment-scale abiotic environmental factors. Natural and intermediate reaches with moderately high levels of sub-catchment urbanization had relatively high biomass, species-rich, and native-dominated fish assemblages whereas concrete-channelized reaches with very highly urbanized sub-catchments had fish assemblages with few to no native species and highly abundant, tolerant, and exotic species.