Multiple factors influencing species interactions in a coral reef ecosystem: Implications for the dominant grazer, Sparisoma viride

Recent empirical studies have demonstrated that human activities such as overfishing and mangrove deforestation can strongly affect the natural capital and services associated with reef ecosystems. In the Caribbean, marine reserves alter trophic interactions by shifting fishing patterns which lead to increased biomass of large-bodied parrotfishes, despite the increased abundance of large piscivores within their borders.  This then increases grazing which results in greater reef resilience through enhanced recruitment and survival of corals. Also, the presence of mangroves, which serve as an intermediate nursery habitat, can modify the structure of fish communities on adjacent coral reefs and lead to an increase in adult biomass of several commercially important species.  Although these empirical relationships are relatively well understood by themselves, there has not been an attempt to integrate these factors in an applied theoretical framework. We develop a simple trophic model to examine how the intensity of fishing pressure in conjunction with the extent of adjacent mangroves will impact the interactions between a representative large piscivore (Nassau grouper, Epinephelus striatus), a species whose adult biomass is enhanced by mangroves (Yellowtail snapper, Ocyurus chrysurus) and a parrotfish (Stoplight parrotfish, Sparisoma viride) on coral reef systems.  This model demonstrates the importance of understanding species interactions in addition to the direct influence of human activities on individual species when attempting to manage for an ecosystem function mediated by a single species, in this case coral reef resilience and the biomass of large-bodied parrotfish. The simplicity of the model is important for drawing general conclusions.