Functional diversity metrics detect spatio‐temporal changes in the fish communities of a Caribbean marine protected area

Abstract

AbstractFunctional diversity (FD) metrics quantify the trait diversity in biological assemblages and act as a proxy for the diverse ecological functions performed in the community. Analyses of FD offer a potentially useful tool to identify functional changes in diverse, complex, and disturbed marine ecosystems such as coral reefs, yet this metric is rarely applied to evaluate community change. Here, we documented spatio‐temporal variability in the trophic function of fish assemblages to identify changes in coral reef communities inside the Buck Island Reef National Monument (BIRNM) in the U.S. Virgin Islands between 2002 and 2010, which included an intense coral bleaching event in 2005. We combined six trait categories related to the trophic function of 95 fish species together with species biomass estimated from underwater surveys to calculate assemblage‐level descriptors of functional richness (FRic), dispersion (FDis), and evenness. We tested the effects of habitat type, time, and their interaction on fish FD using a non−parametric permutational multivariate analysis of variance. We found statistically significant differences for FRic and FDis between habitat types and survey years. Coral reef and other hard bottom areas supported highest levels of trophic functional richness and variation, but low functional redundancy. Fish species exhibited high functional uniqueness within the functional trait space suggesting that a significant decline in fish diversity in the BIRNM would likely result in loss of trophic functions from the fish community. Detection of temporal variations in functional trait composition subsequent to the mass coral bleaching event in 2005 indicates that FD descriptors are sensitive enough to track shifts in the emergent trophic organization of fish communities. In the BIRNM, the trophic organization in fish assemblages did not return to the pre‐bleaching state even after five years of monitoring. We demonstrate a novel way to monitor resilience to disturbance by plotting and tracking the centroid of the functional trait space through time. Our findings demonstrate the utility of FD descriptors to evaluate changes to the functional integrity of diverse and spatially heterogeneous habitat structure across the seascape.