Can reef fish diversity stay high even after major coral loss?

Details

Certain reef fishes are thought to help reef ecosystems recover after coral mortality. High fish species diversity and the associated diversity of ecological roles are considered a form of “ecological insurance” against ecosystem degradation.

Researchers examined how reef fish communities responded to differing levels of coral decline across 22 individual Great Barrier Reef reefs over 11 years. Using seven measures of species diversity, they found that fish diversity rarely decreased following coral declines, even on seven reefs where coral cover fell by more than 75%.

On those seven reefs, however, maintained diversity concealed major community changes: large herbivorous fish became more abundant, while both coral-dependent fish and species with no obvious dependence on coral became less abundant. The magnitude of changes in species abundance increased linearly with the magnitude of coral decline. The proportions of species that increased or decreased varied considerably among reefs; on some reefs, 45–71% of fish species decreased in abundance.

Because ecological function is related to abundance, the researchers considered these declines likely to indicate reduced ecosystem function. They suggested that reef fish diversity may not be a reliable indicator of reef resilience. They also concluded that predicted declines in coral cover due to global warming are likely to change reef fish community structure, but the nature of those changes and the associated capacity of reef fish to assist ecosystem recovery will vary among reefs.