Functional diversity is a useful tool in ecosystem based management to understand spatio-temporal patterns in the functional organization of biological assemblages, but it needs validation in high diversity systems such as coral reef areas and surrounding habitats. Functional diversity metrics can identify the niche space of species using their relative abundance and values of functional traits while quantifying changes in community characteristics that relate to resilience. We studied spatio-temporal changes in the trophic function of fish assemblages inside the Buck Island Reef National Monument (BIRNM) in the U.S. Virgin Islands between 2002 and 2010. We used 25 functional traits related to the trophic function of 166 fish species and their biomass to calculate descriptors of functional richness and variation. A nonparametric permutational multivariate analysis of variance was used to test for effects of habitat type, year of surveys, and interaction between these two factors on fish functional diversity.
We found that changes in functional diversity are habitat and time dependent among fish communities. Coral reef and hard bottoms supported high trophic functional richness and variation; however, their low functional redundancy suggested that few fish species share specific functional roles, and consequently, fish diversity loss implies loss of trophic functions. Important temporal variations found in functional trait composition during the last decade in the BIRNM suggested that functional diversity metrics are sensitive enough to track the trophic organization of fish communities. We argue that greater effort to describe basic ecological traits of marine fish species at juvenile and adult stages is needed to improve the application of functional diversity concepts on ecosystem based management of marine habitats. Our study made an important contribution to update knowledge on the trophic function of Caribbean fish species, validate descriptors of functional diversity to understand ecosystem changes in marine habitats, and demonstration of useful methods for similar assessments worldwide.