The influence of regional and local processes on reef fish assemblages in the Anthropocene

Coral reef systems are circumglobally distributed within tropical marine regions. Within coral reef ecosystems, evolutionary processes and biotic interactions have shaped a remarkable array of patterns within and among reef biota. These highly productive environments can provide valuable resources and services for human population, yet they are experiencing widespread decline due to climate change and the intensification of other anthropogenic impacts. Reef fishes and hermatypic corals are major marine fauna components within reef ecosystems and play key ecological roles in sustaining reef communities. In this dissertation, I have used coral reefs as a model ecosystem to address the influence of regional and local processes on reef fish community assembly. These results will help to improve our understanding of how reef ecosystem functioning might respond to continued anthropogenic and environmental disturbances over the coming decades. Specifically, I investigated the effects of changes in the distribution of coral morphological traits on i) fish assemblages and ii) fish-coral interactions after multiple disturbances, iii) whether the architecture of reef fish agonistic interactions, a proxy for competition, changes over a gradient of regional diversity, and iv) which aspects of fish larval connectivity are key predictors of ecosystem functioning and therefore relevant to marine conservation planning. After multiple disturbances, I found that changes in the morphological makeup of reef-building corals have negatively impacted juvenile reef fish abundance, particularly of small-bodied species. Coral and fish morphological and life-history traits, respectively, were key factors structuring these biotic interactions. While both home range and fish trophic traits shaped the structure of agonistic interactions among reefs fishes, the relationship between fish body size and coral morphological complexity influenced the structure of fish-coral associations. Nonetheless, the importance of coral traits in structuring fish-coral interactions became less evident after multiple environmental disturbances. Regional processes operating at larger temporal and spatial scales, such as the evolutionary history of species and potential fish larval dispersal among reefs, played an important role in predicting the structure of biotic interactions and fish richness and standing biomass on coral reefs worldwide. The number of species engaging in disputes for reef resources was higher on coral reefs with high regional species richness. Moreover, biodiverse and productive reefs were widely connected with several other reefs and displayed a higher potential for larval importing than exporting (e.g. ‘sinks’). Collectively, the results presented in this thesis demonstrate the influence of local and regional scale processes on reef fish community assemblages. It is anticipated that these findings may shed some light on the optimal design of future integrative frameworks and conservation strategies for protecting future coral reefs from the unprecedented impacts of climate change and other anthropogenic pressures.