Functional vulnerability and biogeography of reef fish assemblages in the Galapagos Archipelago

Abstract

The Galapagos archipelago's unique reef biodiversity and fish distribution patterns are well documented. However, reef ecosystem vulnerability to losing functional diversity and the biogeographical drivers of community functional diversity are undescribed. The functional diversity and vulnerability of coastal reef fish communities in the Galapagos were investigated using Baited Remote Underwater Stereo-Video systems (stereo-BRUVs). Relative abundance data for 41,594 individual fish belonging to 121 species was collected, 87 functional entities were identified, and functional diversity and vulnerability estimated based on five functional traits. The influence of spatial and environmental variability and human impact on functional entity composition and richness were also assessed.Galapagos reef fish communities have a high vulnerability to reduced functional diversity if species are lost due to the low redundancy and high sensitivity of reef fish functional entities. However, there may be some ecosystem resilience against species loss from species filling ecologically similar niches instead of redundant species filling the same niche. The functional trait structure and vulnerability of Galapagos reef fish assemblages reflect the known trophic structure of the marine food web. Most functional entities with resilience from redundancy include upper trophic level species with piscivorous diets. Most functional entities that are sensitive and represented by only one species include lower trophic level species. Spatial variables relating to marine environmental variation (from tropical to temperate reef ecosystems) and benthic habitat bottom incline were important predictors of reef fish functional entity distribution. Functional vulnerability may be a concern in marine ecosystems where functional diversity is low, including at higher southern latitudes and western longitudes, the cooler temperate regions and topographically simple marine habitats. Our study raises concerns about the long-term functioning of Galapagos marine ecosystems under present climate change and human management scenarios. We suggest grouping species by functional traits for consideration in the future marine management of Galapagos marine communities.