Responses of Coral Reef Fish to Changes in Coral Cover: Australia

Cheal et al. (2008) examined several responses of reef fish communities to varied levels of coral decline -- caused by a combination of crown-of-thorns starfish outbreaks, coral bleaching and cyclones -- which responses were derived from annual surveys conducted over the 11-year period 1995-2005 of twenty-two individual reefs located between 14 and 24°S latitude that comprised parts of Australia's Great Barrier Reef system.

Based on seven different measures of species diversity, Cheal et al. found that "fish diversity rarely decreased due to coral declines, even on seven reefs that suffered massive coral losses," where living coral cover declined by more than 75% in these "worst-case scenarios." What generally did happen was that there were often "increases in abundance of large herbivores and decreases in abundance of both coral-dependent fishes and species with no obvious dependence on coral."

The five researchers write that their findings are "encouraging," in that "maintenance of fish diversity should assist recovery of fish species whose abundances declined with coral cover," and that "maintenance of a wide taxonomic range of species should also confer greater stability on a community during major perturbations through functional redundancy." They speculate, however, that "widespread abundance decreases might lead to loss of ecosystem function," but they add that "the significance of the functional roles of many fish taxa to coral reef resilience is not known, nor is it clear what abundances of fishes are necessary to retain ecosystem services." Consequently, their "compelling" finding that "reef fish diversity was maintained despite large coral declines" must indeed be considered to be "encouraging," as they appropriately described it.