The ecosystem roles of parrotfishes on tropical reefs

Global reductions in biodiversity and the accelerating loss and degradation of many of the world's ecosystems have intensified research into the roles of species in ecosystem processes. Within coral-reef systems, the parrotfishes (Labridae) are widely viewed as a key functional group in facilitating the recovery of reefs from recurrent disturbances. Although parrotfishes are commonly viewed as herbivores, exerting top-down control of algal communities, their unique jaws allow them to feed on almost all coral- reef substratum types. Consequently, parrotfish are the primary agents responsible for a number of key ecological processes on coral reefs, namely, bioerosion, sediment production and transport, provision of space for coral settlement, and predation of live coral colonies. The parrotfishes, however, cannot be considered a uniform group. Their functional roles are highly dependent on species feeding mode (scrapers, excavators, and browsers) and body size, with larger individuals having a disproportionately greater effect on the dynamics of benthic communities than smaller conspecifics. Parrotfish are ubiquitous on tropical reefs worldwide, yet there is strong spatial structuring in the taxonomic and functional composition of the group. This spatial variation has been shaped by their biogeographic history, the productivity of their environment, and the habitat requirements of individual taxa. Over recent decades, increasing fishing pressure and habitat destruction have had a dramatic impact on the structure of parrotfish assemblages, and as a consequence, on many reefs, normal ecosystem processes have been disrupted. Indeed, reef systems with severely depleted parrotfish communities are less resilient to anthropogenic or natural environmental perturbations. Management strategies for the protection of this unique and critical functional group are urgently needed if we are to maintain the diversity, resilience, and structure of coral-reef ecosystems