School of Natural and Environmental Sciences


Impacts of coral bleaching on coral reef fish assemblages in the Western Indian Ocean

Perhaps the most tightly-linked consequence of global warming at the current time is coral bleaching. Increases in sea-surface water temperature are pushing corals over their thermal limits, causing them to reject their symbiotic algae and widely killing them. Bleaching is becoming more frequent, the 1998 event affecting all coral reef regions of the world and resulting in mortality of 16% of the world’s reefs. Coral reefs are among the most diverse ecosystems on earth and people in many tropical countries depend on them. Live corals give the reef its structure, providing a habitat matrix for diverse assemblages of animals. Once the coral dies the reef is much more susceptible to erosion, both by bioerosion and physical stresses such as storms. Corals also compete for space with algae, the latter often taking over after a bleaching event. Many reef fish depend on live coral, some feeding directly on it, others relying on the refuge it provides from predators or as a site for larval settlement. Other species of fish feed directly on algae and may be positively affected by the bleaching events, at least in the short term. To date the few studies that have looked at this topic have either been small scale and biologically narrowly focused, or have been conducted too soon post bleaching to account for the breakdown in structural complexity of the reef. This is better defining relationships between coral reef fish and their habitat, by investigating what happens to fish assemblages in the medium- to long-term when corals bleach. 

Specifically, it will answer the following questions:

  1. Are the densities of species that feed on live coral and other coral specialists affected by bleaching and if so how?

  2. Do increases in algae affect herbivore densities and in what ways?

  3. Are species targeted by fishing affected by bleaching, if so which are, and what are their ecological characteristics?

  4. How is substrate complexity affected and does this influence fish diversity, abundance and biomass?

  5. Do higher fishing intensities reduce the likelihood of recovery in both the fish and coral communities?