Thesis abstract:

«p»Coral reefs are threatened by anthropogenic climate change, resulting in mass coral bleaching and loss of structural complexity. Reef fish consequently suffer from reduced food availability and loss of habitats. In this context, corallivorous fishes are perhaps the most impacted trophic group but gain less attention despite tight interactions with coral. The abundance of corallivores is often positively correlated with their preferred food, tabular or branching corals, which contribute highly to the structural complexity of reefs. However, higher structural complexity is associated with a higher density of large piscivores. The presence of predatory fishes may lead to feeding avoidance by corallivores and, thus, a subsequent decreased corallivory rate. It remains poorly understood how increases in food availability and predation risks change the corallivory rate and how these feedbacks vary across different habitats. Corallivorous fishes are viewed as sources of chronic stress to coral. Studies have shown the negative impacts of corallivorous fishes on the growth and biomass of coral nubbins, but little is known about how they influence the overall fitness and structure of whole coral colonies. In addition, how these trophic interactions differ among different types and life stages of corallivores is yet to be tested. Such knowledge is critical to accurately assess the extent to which corallivory may impact the susceptibility of coral to bleaching or recovery trajectories. Hence, my Ph.D. project comes with four objectives, aiming to disentangle interactions and identify potential feedbacks between corallivorous fishes and scleractinian corals using field-based and tank experiments. The first objective is to capture the broad-scale pattern of corallivory rate and piscivore prevalence among different reefs across the GBR and the Torres Strait. The second objective is to link the within-reef structural gradient to corallivory rate and piscivore prevalence with consideration of within-day variations at One Tree Island. The third objective is to investigate how different life stages and predation intensities of a corallivorous butterflyfish impact the structure and physiological performance of coral colonies. The fourth objective is to quantify how corallivory of different corallivores impacts the above traits and how corallivory changes under predation risks. Overall, this study will enable a better understanding of the underestimated but important roles of corallivorous fishes and may further assist in predicting future reef trajectories.«/p»