Reconstructing baselines for Caribbean predatory reef fishes

The natural, pre-human, abundance of most large predators is unknown due to the lack of historical data and the poor understanding of the natural factors that control their populations. We assessed the relationship between the biomass of predatory reef fishes and several anthropogenic and environmental variables to (1) predict among site variability in predator abundance in response to both human impacts and natural factors, and (2) estimate historical baselines of fish predator biomass in the absence of humans. We hypothesized that predatory fish abundance declines with human influence but is also strongly associated with natural environmental variability. We assessed the biomass structure of reef fishes at 39 sites over three years across the greater Caribbean. Using generalized linear mixed effect models, we examined the relationships between the biomass of predatory reef fishes and a comprehensive set of 29 anthropogenic, physical, spatial, biotic, and management-related covariates. We used the best explanatory models to predict the biomass of fish predators in the absence of humans. Predatory reef fish biomass was higher in marine reserves but strongly negatively related to human impacts, especially coastal development. Over 50% of the variability in predator biomass, however, was also explained by non-human factors including reef complexity, ocean productivity, and prey abundance. Comparing site-specific predicted values to field observations suggests predatory reef fish biomass has declined by 80-95% in most sites, even within most marine reserves. Bottom-up forces are critical (yet often overlooked) drivers of reef fish communities across gradients of human exploitation. This suggests that we could underestimate historical biomass at sites that provide ideal conditions for predators or greatly overestimate that of seemingly predator-depleted sites that may have never supported large predator populations due to suboptimal environmental conditions. We highlight areas that are natural “hot spots” of predator biomass that can be targeted for strategic protection and restoration.