EFFECT OF URBANIZATION ON TROPICAL STREAM HABITATS AND THEIR ASSOCIATED DRAGONFLY FAUNA IN PUERTO RICO

Urbanization is a major land use type that has considerable impacts on stream ecosystems and their species richness and abundance. Streams in urban settings are affected by multiple stressors: flow modifications, nutrient concentrations, and loss of riparian vegetation. Aquatic insect richness and abundance directly reflect these alterations and can be used to assess urban impacts on streams. Dragonflies are important predators in aquatic environments, and they serve as links between aquatic and terrestrial environments. Unfortunately, the effects of urbanization on dragonfly richness and abundance in the tropics are poorly understood. The objective of this study is to determine the effects of urbanization on stream habitat quality and associated dragonfly assemblages. A total of 15 streams along a rural-urban gradient were characterized using a modified version of the Stream Visual Assessment Protocol (SVAP) for Puerto Rico. A 100m reach of each stream was surveyed for 30min to assess adult dragonfly richness and abundance during the months of September and October. Adults were identified visually on the fly and their abundance was recorded. Preliminary results suggest the adapted SVAP for the island resulted in a clear rural-urban gradient. Dragonfly richness ranged from 2 to 9, and abundance from 5 to 323. The index positively correlated to abundance, but not with richness. Overall, our study indicates dragonfly assemblages are not diverse in urban areas and are affected by changes in stream habitat condition because of urbanization