Fire corals can be the bane of a diver’s existence. Accidental contact with one of them can cause excruciating pain. But they can also help save Caribbean reefs, which have been plagued by hurricanes, global warming, disease and an overabundance of algae. A long-term study found that fire corals (Millepora) are thriving there even as other corals are disappearing and could help preserve some of the 3D environment that helps make reefs such beautiful homes for fish and other organisms.
Fire corals “are going to be very important habitat providers because they’re able to survive under those stresses,” says Colleen Bove, a marine ecologist at Boston University who wasn’t involved in the work.
Thirty years ago, Peter Edmunds began conducting annual underwater life surveys off St. John, one of the US Virgin Islands. California State University marine biologist Northridge traced a 20-meter transect along an underwater reef. Each summer he photographed what grew there, including a 40-meter widened transect.
By analyzing the abundance of each organism in these “photoquadrats”, Edmunds traced how algae and various corals have withstood hurricanes, warming sea temperatures and other environmental stresses. “What he did is really remarkable,” says Caroline Dubé, a marine biologist at Université Laval who studies the plasticity of Pacific fire coral. “There’s so much disturbance to coral reefs that it’s something that needs to be done more.”
Fire corals look like typical hard corals but are actually close relatives of jellyfish; hence their nasty sting. They have the ability to grow either as leaves—spreading like a flat covering over rocks and other surfaces—or as “trees,” growing upwards with a stem and branches. More than 40 years ago, Jeremy Jackson, an ocean biologist at the American Museum of Natural History and the Smithsonian Tropical Research Institute, proposed that this plasticity would give fire corals an advantage as Caribbean reefs experience global warming. and hurricanes. Edmunds now concludes that Jackson was right.
Overall, Edmunds’ long-term data indicates that many types of multicellular algae called macroalgae have invaded Caribbean reefs. But if hurricanes or other factors destroy macroalgae, fire corals move quickly and encrust surfaces, Edmunds reports today in the Proceedings of the Royal Society B. When the reef is crowded, the coral grows in its branching tree form, so it can continue to thrive in tight spaces and provide vertical structure for other organisms to nibble, live on, or otherwise use.
Periodically, unusually warm water causes corals to lose their green algal partners and die, setting the stage for macroalgae to re-establish themselves. Hurricanes also blow on the branches of the tree. But fire coral is quickly coming back in one form or another, Edmunds found. Thus, this coral was able to maintain itself and even increase a little in abundance.
“Their stony coral buddies don’t do a great job with leaf and tree production,” Edmunds says. “So in a world with frequent storms and fierce competition for bottom space, fire corals are poised to inherit shallow reefs.”
Jackson is thrilled: “Edmunds’ remarkable persistence has allowed him to witness the ups and downs of fire coral dynamics.” Unfortunately, Edmunds’ data also shows that other corals are becoming increasingly rare. “Millepora could replace them as they decline due to marine heat waves and coral bleaching,” says Jackson.
This may still be bad news for reefs in general. Nikolaos Schizas, a marine scientist at the University of Puerto Rico, Mayagüez, warns that fire corals may not save reefs because they don’t usually form reefs several meters high and wide. “We have to be realistic about the magnitude of that potential,” says Schizas.
Edmunds’ data also reveals that fire corals have been repeatedly toppled by hurricanes and other disturbances, points out Terry Hughes, marine scientist at the Australian Research Council’s Center of Excellence for Reef Studies. corals. “But the study strongly suggests that they will fare better than the majority of corals.”