Predator effects on faunal community composition in shallow seagrass beds of The Bahamas

Much emphasis has been placed on predator effects that cascade through food webs. Such top-down effects seem to be most common in systems with relatively simple food chains, and rarer in species-rich systems where numerous weak interactions among species can buffer strong top-down effects. Seagrass ecosystems are typically species-rich and characterized by complex food webs, but evidence of top-down effects in these systems has been mixed. We examined effects of predatory fishes on the species richness, biomass, density, and composition of the epifaunal community in a shallow seagrass ecosystem of The Bahamas. We used exclusion experiments at two different spatial scales, and applied mesh sizes that excluded different-sized predator individuals. We found some evidence of species-level top-down effects (i.e., strong interactions within a subset of the community), driving higher biomass in at least one decapod mesopredator. In contrast, community-level predator effects were rather weak, with predator size and spatial scale of experiments displaying no detectable impact on the overall epifaunal community. Multiple factors may have contributed to these patterns, including high species richness, relatively shallow water depth, small-scale spatial variation in habitat features, and the size and abundance of predators. Because of the rapid global decline of seagrasses and their associated fauna, increased knowledge of predator effects on faunal communities of seagrass beds is critical for long-term conservation efforts.