Drivers of reef fish assemblages in an upwelling region from the Eastern Tropical Pacific Ocean

Reef fish assemblages are exposed to a wide range of anthropogenic threats as well as chronic natural disturbances. In upwelling regions, for example, there is a seasonal influx of cool nutrient-rich waters that may shape the structure and composition of reef fish assemblages. Given that climate change may disrupt the natural oceanographic processes by altering the frequency and strength of natural disturbances, understanding how fish assemblages respond to upwelling events is essential to effectively manage reef ecosystems under changing ocean conditions. This study used the baited remote underwater video stations (BRUVS) and the traditional underwater visual census (UVC) to investigate the spatiotemporal patterns of reef fish assemblages in an upwelling region in the North Pacific of Costa Rica. A total of 183 reef fish species from 60 families were recorded, of which 166 species were detected using BRUVS and 122 using UVC. Only 66% of all species were detected using both methods. This study showed that the upwelling had an important role in shaping reef fish assemblages in this region, but there was also a significant interaction between upwelling and location. In addition, other drivers such as habitat complexity and habitat composition had an effect on reef fish abundances and species. To authors’ knowledge, this is the first study in the Eastern Tropical Pacific that combines BRUVS and UVC to monitor reef fish assemblages in an upwelling region, which provides more detailed information to assess the state of reef ecosystems in response to multiple threats and changing ocean conditions.