Urban Impacts on Tropical Island Streams: Key Aspects Influencing Ecosystem Response

Few studies have considered the unique responses of tropical island streams to urbanization. We identified three key aspects that play particularly important or unique roles in determining tropical island stream integrity in the face of urbanization: movement barriers along the stream network, biotic response to water pollution and physical habitat alteration and loss. Movement barriers along the stream network are especially important as many tropical island freshwater fauna (mollusks, shrimps, and fishes) have diadromous life histories. As expected, water pollution negatively impacts stream ecosystems in tropical islands and in some regions impacts can be severe.  While aquatic insects show expected responses to pollution, diadromous assemblages appear to be less impacted by pollution. Finally, in streams that are connected to the marine environment the presence of native shrimps and fishes is strongly related to the physical habitat.  Fish assemblages in channelized and severely altered stream reaches are largely devoid of native fauna and dominated by introduced species yet relatively diverse shrimp and fish assemblages can be found in reaches that retain some habitat complexity, even when impacted by urbanization.  Understanding the key aspects of urban impacts tropical island streams can help focus management and research efforts to protect these unique ecosystems.