Abstract: Following disturbances, coral reefs may recover or remain degraded in a range of conditions. Two ecological processes (recruitment and herbivory) have been suggested to be highly influential in determining a reef’s propensity for recovery – successful recruitment of coral larvae is required to replenish depauperate populations, and sufficient levels of herbivory to either prevent or reverse macroalgal competition. The aim of my thesis is to use the extensive variability in reef condition that exists on reefs of the inner Seychelles islands to understand the role of communities shaping key ecological reef processes. I first quantitatively assessed the variability in reef condition, considering a reef’s underlying substrata, benthos, and associated fish assemblages. I found strong relationships between a reef’s benthos and associated fish assemblage. There was a gradient from degraded reefs with low coral cover and fish species richness, yet high macroalgal cover (hereafter macroalgal-dominated reefs), to reefs with high coral cover and high fish species richness (hereafter coral-dominated reefs). I then used reefs exhibiting these more extreme conditions to measure levels of incoming coral recruitment and coral juvenile densities. I found that macroalgal-dominated reefs were receiving the same number of recruits as coral-dominated reefs, but these recruits were either unable to settle successfully on the natural substrate, or survive through to their juvenile life stage. The presence of abundant macroalgae on reefs is therefore likely to be having detrimental effects on coral replenishment following disturbances. I performed a comparison of macroalgal herbivory on coral- vs. macroalgal-dominated reefs using bioassays. I found that the macroalgal herbivore assemblage differed significantly between the two reef conditions and that the proportion of the assay removed was significantly lower on macroalgal-dominated reefs. Finally, I resurveyed all the reef sites two years after the initial surveys to investigate dynamics of the strong relationship between a reef’s benthos and fish assemblage. My research emphasises the long-term detrimental effects of reef degradation, especially phase shifts to macroalgal-dominance, on important ecological processes. In doing so, the work also highlights areas or time periods where management strategies may be most effective.

Biography: Karen is from the Seychelles, but has lived in Townsville for a while now. She originally came out to Australia to do her undergraduate degree, but received opportunities to delve into research and stayed. Her honours thesis investigated coral reef fishes and coral disease on the GBR. Her PhD has taken back to the Seychelles to take advantage of a highly varied system; perfect for trying to understand why some reefs recover after disturbances, whereas others don’t. She is supervised by Nick Graham, Morgan Pratchett and David Bellwood.