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Researchers at UCSB’s Marine Science Institute recently discovered a link between the behavior of algae-eating fish and the resiliency of coral reefs.
At the Moorea Coral Reef in French Polynesia, one of 26 sites of the multi-university Long Term Ecological Research Network funded by the National Science Foundation, the team observed that the region’s herbivorous fish eat algae from around the reef, clearing the way for its growth. Coral reefs worldwide have suffered a general decline due to cyclones, climate change, ocean acidification and other factors, but the coral cannot always recover because algae typically builds up in its place.
According to Sally Holbrook, an ecology, evolution and marine biology professor at the MSI, a combination of cyclones and crown-of-thorns sea stars significantly reduced coral coverage in Moorea’s outer sections.
“The outer reefs went from 40 to 45 percent coral coverage — which is a lot — to almost nothing, although the inshore reefs were less affected,” Holbrook said.
Despite this substantial reduction, the corals are beginning to make a comeback. Postdoctoral associate Tom Adam, a researcher at the MSI, said the LTERN researchers discovered that species such as parrotfish and surgeonfish are bigger and more numerous in Moorea’s network of reefs and have been feasting on the algae that normally stunts regrowth.
“The algae quickly comes in and takes over,” Adam said. “But in the case of Moorea, the grazing by these fish was preventing the algae from reaching a level of coverage that kept baby corals from growing.”
The algae-consuming fish grow up in fringe reefs close to shore and migrate toward floor reefs such as the Great Barrier Reef or outer reefs such as at Moorea.
MSI assistant research biologist Andrew Brooks said efforts to protect reefs focus largely on setting up Marine Protected Areas around the bigger reefs where the adult fish live but often neglect to look after inshore reefs where the fish grow up, indicating a need for greater protection of these nursery areas.
“You can protect the adults all you want,” Brooks said. “But if you don’t protect the smaller baby fish then there won’t be any adults that make it out to the floor reefs.”
The research team published its findings on Aug. 25 in the scientific journal PLoS ONE.
Holbrook said the research group aims to further understand the coral’s growth patterns in relation to the fish population.
“Now the important thing will be to look at how rapidly [the coral] grows and what species of coral will grow,” Holbrook said.