Jacob Allgeier. Image credit: Dale Austin

How can we boost the resilience of the world’s coral reefs, which are imperiled by multiple stresses including mass bleaching events linked to climate warming?

One strategy advocated by some researchers, resource managers and conservationists is to restore populations of algae-eating reef fish, such as parrotfish. Protecting the fish that keep algae in check leads to healthier corals and can promote the recovery of distressed reefs, according to this idea, which is known as fish-mediated resilience.

But a new study that analyzed long-term data from 57 coral reefs around the French Polynesian island of Mo’orea challenges this canon of coral reef ecology.

The study, published online Oct. 3 in the journal Nature Ecology & Evolution, provides compelling new evidence that fish don’t regulate coral over time, according to University of Michigan marine ecologist and study co-senior author Jacob Allgeier. The other author is former U-M postdoctoral researcher Timothy Cline.

“This paper very well might radically change how we think about the conservation of coral reefs,” said Allgeier, assistant professor in the U-M Department of Ecology and Evolutionary Biology.

“People have been saying for years that we can protect coral through fisheries management, and our work on Mo’orea reefs shows that this is unlikely to work—there are too many other things going on. There is functionally no measurable effect of fishes on coral cover over time.”

Support for the idea of fish-mediated coral reef resilience has led to calls for moratoriums on fishing for algae-eating reef fish to prevent algae overgrowth and reef degradation. Such well-intentioned but misguided management strategies could have huge implications for the millions of people who depend on coral-reef fisheries for food and income, according to the authors of the new study.

Instead, it makes more sense to support strategies that promote the conservation of diverse habitats and coral reef types at various stages of degradation, the researchers said.

“We do need to manage fisheries in these ecosystems, but instead of things like wholesale restrictions on parrotfish, we should consider management efforts that promote sustainable harvest throughout the food web to disperse the impacts of fishing,” Allgeier said.

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