Study finds reef-fish diversity fights coral disease

Sharknose goby (Elacatinus evelynae) resting on a boulder brain coral (Colpophyllia natans). Image credit, Laszlo Ilyes.Outbreaks of infectious diseases in coral have emerged as a major cause in the decline of reefs worldwide.  Now, a groundbreaking study  in the Proceedings of the National Academy of Sciences finds that a diverse fish community reduces the level of coral disease compared to an overfished reef.

Scientists from the University of Guam and the University of Hawaii at Manoa hypothesized that overfishing reduces the resiliency of coral reefs to disease by removing groups of fish that play important functions in the ecosystem (e.g. as predators that regulate the numbers of other species). To test the hypothesis that functionally diverse fish communities play a role in ameliorating coral disease, the researchers surveyed 14 sites in the Philippines including 7 marine protected areas and 7 adjacent fished areas. The researchers found that:

• Marine protected areas had a powerful effect on reducing coral disease, with significantly lower disease prevalence than that of unprotected sites.

• The presence of coral disease was most strongly reduced on reefs completely protected from fishing.

• Evan among fished reefs, those with greater fish diversity, on average, were less diseased.

• These results were not due to differences in percent total coral cover, physical damage to corals. or benthic attributes.

The study also found that disease prevalence was negatively correlated with fish taxonomic distinctness at the sites (i.e. the less taxonomic diversity in the makeup of the fish community, the more likely the occurrence of disease).

Perhaps most interesting, the study found a significant positive relationship between disease prevalence and the butterflyfish family Chatodontidae. The researchers speculate that these fish are more common at taxonomically poor sites because either they're not targets of fishing or they're released by other top-down interactions, and in turn they serve as vectors for coral disease.

The researchers conclude:

Our results demonstrate a clear link between functionally diverse, species-rich fish communities and low disease prevalence. We acknowledge that the effect of fishing on coral health is complex and that the mechanisms by which this occurs require further investigation. Nevertheless, we found that effectively managed marine protected areas had a powerful effect on reducing coral disease by maintaining functionally diverse fish assemblages.

--Reviewed by Rob Goldstein

Raymundo, L., Halford, A., Maypa, A., & Kerr, A. (2009). Functionally diverse reef-fish communities ameliorate coral disease Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0900365106