Résumé
Parrotfishes are a diverse group, with 100 species distributed across the world's tropical and subtropical oceans. There are very few endemic parrotfish species as most species have a wide geographical range. Unlike many other fish groups whose distributions and species richness are shaped by evolutionary history and habitat size, parrotfish species richness is nearly equally controlled on a global scale by sea temperature (SST), and isolation, as well as habitat size and evolutionary history. Over smaller spatial scales, the species richness, abundance and biomass of parrotfish is dependent on the regional species pool, island size, and fishing with further influence of reef type and within reef habitats. Importantly, there are major differences in parrotfish assemblages between the Atlantic and Indo-Pacific, with assemblages in the Atlantic dominated by browsing species, smaller individuals and higher abundances, but lower biomasses than the Indo-Pacific. Parrotfish are also frequently found in adjacent biotopes (mangroves, seagrass, algal beds) in the Atlantic, mainly as juveniles, whereas they are not abundant in these biotopes in the Indo-Pacific. Differences in the structure of parrotfish assemblages and their relationship to environmental variables at different scales, suggest the ecological role of parrotfish may vary across regions.
This chapter examines the organization and the functioning of parrotfish assemblages from the regional to the local scale, based on both existing literature and comprehensive database of field data. It identifies important regional differences in the distribution of parrotfish species and functions. Superimposed on these regional patterns are local- and medium-scale variation in taxonomic and functional richness, abundance and biomass of parrotfishes that relate to environmental factors and fishing. The chapter shows that not only is parrotfish species richness much lower in the Atlantic than the Pacific, but there are fundamental differences in the functional composition of parrotfishes between these oceans. Despite the broad geographic range of most parrotfish species, there are distinct regional differences in the composition of parrotfish assemblages, with the greatest difference being between the Atlantic and Indo-Pacific Oceans. Individual parrotfish species are typically classified into a single feeding mode; however, such groupings overlook the complexities of feeding in this group.