Recent global recognition of the serious and immediate threats facing marine ecosystems has led to concerns regarding the loss of biodiversity within these systems. These concerns have highlighted the need for research to understand the driving forces behind current patterns of marine diversity. This information is vital in order to develop science-based strategies to maintain these ecosystems and their biodiversity. Unfortunately, little is known about how natural diversity varies within the marine environment, due to logistical constraints and traditional unfamiliarity with this environment. Therefore it is imperative that opportunities to address this issue are fully exploited. The applicant has identified a unique opportunity to understand how marine biodiversity varies across large spatial scales in one of the most diverse and threatened ecosystems in the world, coral reefs. Using the world’s largest marine sightings database, this research will map species richness (i.e. total number of species present) for coral reef fish communities across the Caribbean and Tropical Western Atlantic. This work will also map two other key measures of biological diversity, functional and phylogenetic diversity, as well as testing whether these measures are closely related, as is often assumed. A wide variety of environmental data is also available for the region, including climate and anthropogenic data, and these will be thoroughly tested for associations with reef fish diversity. Furthermore, cutting edge β diversity and community assembly analysis will be performed in order to understand the processes that have created the patterns we see today in these reef fish assemblages. Reef fish are considered to be useful indicators of overall patterns in coral reef biodiversity and the proposed research will produce a truly comprehensive analysis of this important and threatened ecosystem, to a level well beyond any that has been performed previously for marine systems.