New research reveals fishing threshold for coral reef resilience

New research reveals fishing threshold for coral reef resilience

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New research by Mary Donovan, an assistant professor at Arizona State University, reveals that fishing herbivorous species such as surgeonfish and parrotfish to less than 80% of their local unfished densities harms the resilience of coral reefs through the overgrowth of algae these fish consume. Photo courtesy of Bert Weeks. Credit: Bert Weeks

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New research by Mary Donovan, an assistant professor at Arizona State University, reveals that fishing herbivorous species such as surgeonfish and parrotfish to less than 80% of their local unfished densities harms the resilience of coral reefs through the overgrowth of algae these fish consume. Photo courtesy of Bert Weeks. Credit: Bert Weeks

Coral reefs are the most biodiverse system in the sea and are essential to the life of many coastal human communities. Half a billion people depend on coral reefs for protection from storms, providing seafood, as well as promoting tourism and recreation.

But climate change is putting the health of coral reefs globally at risk. Rising sea temperatures are causing coral bleaching and death. So, the resilience of coral reefs to climate challenges is critical to our collective future, and new research from Arizona State University has provided greater understanding of a key aspect of coral reef health.

In a research paper published on December 6, 2023, in Proceedings of the Royal Society BArizona State University Assistant Professor Mary Donovan and colleagues report that fishing herbivorous species such as surgeonfish and parrotfish to less than 80% of their local unfished densities harms the resilience of coral reefs through the overgrowth of algae these fish consume.

“There are many mechanisms and processes involved in the relationship between corals and algae,” says Donovan. “But the two compete for space, and herbivores play a key role in maintaining the balance.” “If herbivore abundance is too low, algae can grow uncontrollably and cause many negative impacts on coral reefs.”

While there are other factors that can affect the resilience of coral reefs, such as land-based pollution flowing into the ocean, this new study clearly shows that herbivorous fish populations are essential to ensuring the future of coral reefs and the benefits they provide to people.

The research was conducted through the Hawaii Monitoring and Reporting Collaborative, or HIMARC, and relied on more than 20,000 surveys throughout Hawaii. This work produced results for all reefs across the state, nearly 130,000 sites in total. Donovan says such comprehensive coverage represents a first of its kind.

“HIMARC is special because it is a collaboration between all the organizations that monitor nearshore areas in Hawaii,” she says. “There are many datasets on Hawaiian coral reefs, but before they were combined by HIMARC they were each from different places. Additionally, there were many sites with little or no data, so the state’s entire story cannot be told.”

HIMARC’s work fills these gaps and creates a consensus about the status of Hawaii’s coral reefs that applies directly to management and policy. In terms of policy, the timing of this research is remarkable because a final decision on new statewide fisheries management rules for herbivores is expected on December 8th.

“The decision-making process, led by the Hawaii Department of Water Resources, took more than two years to complete with extensive community involvement,” Donovan says. “This is the first time in a very long time that new statewide fishery regulations have been introduced. Therefore, we are addressing an issue vital to Hawaii with a message that is imperative to getting across to both policymakers and the public.”

Moving forward, HIMARC continues to study the state of Hawaii’s coral reefs, including indicators such as overall fish diversity and biomass. They are also investigating the role of herbivores in mediating coral reef resilience after marine heat waves that cause coral bleaching and coral mortality. They want to determine whether coral reefs with more herbivores have better outcomes.

“Herbivores play critical roles in the ecosystem, so their function must be supported to ensure the future of our coral reefs,” says Donovan. “At the same time, fishing is very important to the people of Hawaii, so the ecosystem role of herbivores must be balanced with maintaining access to fishing. Our results show that herbivores are abundant in some places and that these reefs are healthy. But that is not It’s true everywhere, so sustainable fishing will help ensure healthy places stay healthy and degraded places can recover.

Data for the comprehensive study conducted by HIMARC came from the Coral Reef Assessment and Monitoring Program (CRAMP) at the University of Hawaii, the National Oceanic and Atmospheric Administration (NOAA), the US National Coral Reef Monitoring Program, and the State of Hawaii. Aquatic Resources, University of Hawaii Fisheries Ecology Research Laboratory, including data from a fish habitat use study conducted by the National Oceanic and Atmospheric Administration (NOAA), the U.S. National Park Service, and The Nature Conservancy of Hawaii.

more information:
Mary K. Donovan et al., Evidence on herbivore management for coral reef resilience, Proceedings of the Royal Society B: Biological Sciences (2023). doi: 10.1098/rspb.2023.2101

Magazine information:
Proceedings of the Royal Society B

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