Effects of predator presence and habitat complexity on reef fish communities in The Bahamas

Abstract

Reef ecosystems are highly diverse habitats that harbor many ecologically and economically significant species. Yet, globally they are under threat from multiple stressors including overexploitation of predatory fishes and habitat degradation. While these two human-driven activities often occur concomitantly, they are typically studied independently. Using a factorial design, we examined effects of predator presence, habitat complexity, and their interaction on patch reef fish communities in a nearshore ecosystem on Great Abaco Island, The Bahamas. We manipulated the presence of Nassau groupers (Epinephelus striatus), a reef predator that is critically endangered largely due to overharvest, and varied patch reef structure (cinder blocks with and without PVC) to reflect high or low complexity-four treatments in total. To assess changes in fish community composition we measured fish abundances, species richness, and evenness. We found that predators present and high reef complexity had an additive, positive effect on total fish abundance: fish abundance increased by ~ 250% and 300%, compared to predators absent and low complexity reef treatments, respectively. Species richness increased with reef complexity. Variation in community structure was explained by the interaction between factors, largely driven by juvenile Tomtate grunt (Haemulon aurolineatum) abundances. Specifically, Tomtate grunt abundance was significantly higher on high complexity reefs with predators present, but on low complexity reefs predators present had no effect on Tomtate grunt abundance. Our data suggest that both fisheries management of large-bodied piscivores and reef habitat restoration are critical to the management and conservation of reef ecosystem functions and services.