Effect of urbanization on Odonata assemblage composition in a tropical island

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, changes in 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. Odonates are important predators in aquatic environments, and they serve as links between aquatic and terrestrial environments. Unfortunately, the effects of urbanization on odonate richness and abundance in tropical islands is poorly understood. The objective of this study is to determine the effects of urbanization on stream habitat quality and associated odonate assemblages in Puerto Rico. A total of 16 streams along a rural-urban gradient in the San Juan Metropolitan area (SJMA) were characterized using the Stream Visual Assessment Protocol (SVAP) for Puerto Rico. A 100m reach of each stream was surveyed twice for 30min to assess adult odonate richness and abundance during the rainy (2018) and dry (2019) seasons. Adults were identified visually on the fly and their abundance was recorded. Odonate richness ranged from 2 to 9, and abundance from 5 to 382. The SVAP positively correlated to abundance, but not to richness. Even though adult abundance and richness were higher in the dry season, these were not found to be statistically significant. Overall, our study indicates odonate assemblages are not diverse in the SJMA and are affected by changes in stream habitat condition because of urbanization