Biotic resistance, the process by which new colonists are excluded from a community by predation from and/or competition with resident species, can prevent or limit species invasions. We examined whether biotic resistance by native predators on Caribbean coral reefs has influenced the invasion success of red lionfishes (Pterois volitans and Pterois miles), piscivores from the Indo-Pacific. Specifically, we surveyed the abundance (density and biomass) of lionfish and native predatory fishes that could interact with lionfish (either through predation or competition) on 71 reefs in three biogeographic regions of the Caribbean. We recorded protection status of the reefs, and abiotic variables including depth, habitat type, and wind/wave exposure at each site. We found no relationship between the density or biomass of lionfish and that of native predators. However, lionfish densities were significantly lower on windward sites, potentially because of habitat preferences, and in marine protected areas, most likely because of ongoing removal efforts by reserve managers. Our results suggest that interactions with native predators do not influence the colonization or post-establishment population density of invasive lionfish on Caribbean reefs.

Overfishing has eliminated up to 90% of predatory reef fishes, but recovery potential is still high in several Caribbean reefs.

Biotic resistance is the idea that native species negatively affect the invasion success of introduced species, but whether this can occur at large spatial scales is poorly understood. Here we re-evaluated the hypothesis that native large-bodied grouper and other predators are controlling the abundance of exotic lionfish (Pterois volitans/miles) on Caribbean coral reefs. We assessed the relationship between the biomass of lionfish and native predators at 71 reefs in three biogeographic regions while taking into consideration several cofactors that may affect fish abundance, including among others, proxies for fishing pressure and habitat structural complexity. Our results indicate that the abundance of lionfish, large-bodied grouper and other predators were not negatively related. Lionfish abundance was instead controlled by several physical site characteristics, and possibly by culling. Taken together, our results suggest that managers cannot rely on current native grouper populations to control the lionfish invasion.

A variety of factors have caused the loss of corals and fishes on coral reefs, resulting in ecological, social, and economic consequences for reef ecosystems and the people who depend on them. A widely employed management action to restore reef communities is the implementation of marine protected areas (MPAs). We measured the effectiveness of the MPA network in Belize in promoting increases in fish and coral populations and identified key ecological and environmental factors that influence reef community structure and potentially protection success. From 2009 to 2013, we annually surveyed 16 reefs in Belize, including 8 MPA sites (where extractive fishing is limited or prohibited) and 8 unprotected sites. At each site, we quantified the biomass of reef fishes, coral and macroalgal cover, and several biotic and abiotic variables that are known to affect reef inhabitants. High predatory reef fish and parrotfish biomass values were associated with high reef structural complexity and low wave exposure. Mean macroalgal cover was negatively associated with parrotfish biomass in 1 protected zone. However, mean macroalgal cover remained above 40% across all sites, and no change in coral cover was observed during the study. Our results indicate that fisheries restrictions alone do not lead to increases in coral cover even when successful for fishes. We speculate that both illegal and legal fishing may be compromising Belize's MPA network goals. Furthermore, we suggest that species composition as well as local environmental conditions play key roles in coral reef recovery and should be considered when evaluating management strategies.

Fishing is widely considered a leading cause of biodiversity loss in marine environments, but the potential effect on ecosystem processes, such as nutrient fluxes, is less explored. Here, we test how fishing on Caribbean coral reefs influences biodiversity and ecosystem functions provided by the fish community, that is, fish-mediated nutrient capacity. Specifically, we modelled five processes of nutrient storage (in biomass) and supply (via excretion) of nutrients, as well as a measure of their multifunctionality, onto 143 species of coral reef fishes across 110 coral reef fish communities. These communities span a gradient from extreme fishing pressure to protected areas with little to no fishing. We find that in fished sites fish-mediated nutrient capacity is reduced almost 50%, despite no substantial changes in the number of species. Instead, changes in community size and trophic structure were the primary cause of shifts in ecosystem function. These findings suggest that a broader perspective that incorporates predictable impacts of fishing pressure on ecosystem function is imperative for effective coral reef conservation and management.