Trophic cascade facilitates coral recruitment in a marine reserve

Abstract

Reduced fishing pressure and weak predator-prey interactions within marine reserves can create trophic cascades that increase the number of grazing fishes and reduce the coverage of macroalgae on coral reefs. Here, we show that the impacts of reserves extend beyond trophic cascades and enhance the process of coral recruitment. Increased fish grazing, primarily driven by reduced fishing, was strongly negatively correlated with macroalgal cover and resulted in a 2-fold increase in the density of coral recruits within a Bahamian reef system. Our conclusions are robust because four alternative hypotheses that may generate a spurious correlation between grazing and coral recruitment were tested and rejected. Grazing appears to influence the density and community structure of coral recruits, but no detectable influence was found on the overall size-frequency distribution, community structure, or cover of corals. We interpret this absence of pattern in the adult coral community as symptomatic of the impact of a recent disturbance event that masks the recovery trajectories of individual reefs. Marine reserves are not a panacea for conservation but can facilitate the recovery of corals from disturbance and may help sustain the biodiversity of organisms that depend on a complex three-dimensional coral habitat.biodiversity ͉ coral reef ͉ grazing ͉ predation M arine reserves have become one of the most widely adopted tools for managing commercially important fishes and protecting marine biodiversity (1). Several direct effects of reserves are relatively straightforward to anticipate: Reduced fishing mortality usually increases the biomass of target and bycatch species of fishes (2, 3), and reserve status may help prevent acute anthropogenic disturbance such as destructive fishing practices that damage benthic communities (4). However, by enhancing the abundance of fishery species, reserves may also exert indirect impacts on other nonfishery species that naturally interact with fishery species through processes of predation and competition (5).Because the indirect effects of reserves on biodiversity arise from species interactions and trophic cascades (6), they are generally complex and may have surprising outcomes (7,8). We reported such complex outcomes in a study of The Bahamas' Exuma Cays Land and Sea Park (ECLSP), which, at 442 km 2 , is one of the largest and most successful marine reserves in the Caribbean. The ECLSP is a rare example in which sustained fisheries exclusion has resulted in a high biomass of predatory fishes (2 kg per 100 m 2 ). Our a priori hypothesis was that high levels of piscivorous fishes such as the Nassau grouper (Epinephelus striatus) would exert top-down predatory impacts on grazing fishes (a prey item) and, by reducing the biomass of grazers, promote increases in the cover of macroalgae. However, the hypothesis was not supported because large-bodied species of grazer (parrotfish) were found to experience a size-escape from predation, and therefore the expected negative effects of trophic casc...

Macroalgal terpenes function as allelopathic agents against reef corals

“…Recent analyses suggest that marine protected areas may promote local processes, such as herbivory and coral recruitment (39,40), that limit macroalgal proliferation and promote coral recovery, thereby bolstering coral resilience to large-scale disturbance (7,8,11,41,42). However, because several allelopathic macroalgae (e.g., Dictyota, Chlorodesmis, Galaxaura, Lobophora, Halimeda, Ochtodes) also contain toxins that deter some herbivores (43), developing effective marine reserves may require protecting a diverse herbivore guild that includes species that consume chemically defended macroalgae (18,33,43).…”

Tropical Coastal Habitats as Surrogates of Fish Community Structure, Grazing, and Fisheries Value

“…Such intra-habitat variation may, therefore, have considerable ecological importance. For example, grazing intensity is positively correlated with natural rates of coral recruitment (Mumby et al 2007a), and suggests that intra-habitat variation in grazing may influence the potential recovery rates of corals from disturbance, such as hurricanes. The implication for marine reserve planning is that some areas of Montastraea reef may be much more able to recover from disturbances than others, and could be prioritized within reserve selection algorithms.…”

Status of the fringing coral reefs in the southern Egyptian coast of the Red Sea

“…Several studies have demonstrated a critical role of herbivores reef fishes in influencing competitive interactions between corals and algae (Mumby et al, 2006(Mumby et al, , 2007Hughes et al, 2007Hughes et al, , 2011, and consequently coral reef resilience (Nyströ m and Folke, 2001;Bellwood et al, 2004). Many of these studies have demonstrated a strong negative relationship between fish grazing intensity (particularly biomass) and algal cover with increasing in coral cover (Arnold, 2010;Smith, 2010;Mumby and Steneek, 2011).…”