Coral Reefs Host a Vast Diversity of Microbes

A two-year expedition at sea uncovered more than half a million varieties of microbial life in Pacific reef-dwelling organisms

Fish swim over a coral reef
A coral reef in Honolulu, Hawaii. Half of global coral coverage has disappeared since the 1950s. Donald Miralle via Getty Images

Imagining a coral reef might bring to mind scenes teeming with fish, crustaceans and sea anemones. But scientists recently discovered these valuable marine habitats also host massive amounts of living things that are too small for humans to see. Coral reefs, they say, are home to incredible microbial diversity.

Between 2016 and 2018, a group of researchers sailed the Pacific Ocean to better understand the microbes—or tiny organisms including bacteria and archaea—that live on coral reefs.

The team sampled three types of coral, two species of fish and plankton from 99 reefs across 32 Pacific islands. DNA sequencing revealed more than 542,000 different types of microbes living on these organisms. The scientists shared their analysis in a collection of papers published earlier this month.

By extrapolating these findings, the researchers estimate that around 2.8 million kinds of microbes could live on corals and fish across the whole Pacific Ocean, writes Science News’ Erin Garcia de Jesús.

“The microbial biodiversity in this ecosystem is really enormous,” Serge Planes, a co-author of the study and population geneticist at the University of Perpignan in France, tells USA Today’s Dinah Voyles Pulver.

This new, ocean-wide estimate falls within the predicted range for the entire planet’s microbial diversity, the researchers write in a paper in Nature Communications. The results “indicate the microbiodiversity on Earth is underestimated,” Pierre Galand, a co-author of the study and microbiologist at Sorbonne University in France, said on a press call with reporters, per Inverse’s Tara Yarlagadda.

Still, the researchers might not have been able to capture all the microbial diversity in Pacific reefs, as Jennifer Biddle, a microbial ecologist at the University of Delaware who was not involved in the project, tells Science News. “We’re always undercounting microbes with the methods we’re using.”

Though corals might not look like it, they’re actually alive. Each branch or mound of coral is a collection of thousands of tiny animals known as polyps. These organisms use calcium carbonate from the water to build protective skeletons, according to the Office of National Marine Sanctuaries.

Coral reef ecosystems host a diverse array of life—they’re home to more than a million animal species, including sponges, oysters, crabs and many types of fish, according to the Environmental Protection Agency. While they cover only 0.2 percent of the ocean floor, coral reefs contain a third of all species living in the ocean, Planes tells USA Today.

But coral reefs are dying. Since the 1950s, half of global coral coverage has disappeared due to climate change and human activity, according to the paper.

“Coral reefs are … an ecosystem in crisis,” Planes tells Inverse. “We need to understand their biodiversity.”

On their expedition, the researchers gathered 5,392 samples of fire coral, lobe coral, cauliflower coral, plankton, bacteria and two fish species, the convict tang and Moorish idol, writes USA Today. Despite only looking at these specific animals, the scientists observed enough bacteria to roughly equal 20 percent of the estimated total types of bacteria living on Earth, per Science News, which underscores just how plentiful these microorganisms are.

Microbes play an important role in coral reef ecosystems—bacteria contribute to coral reef health by helping acquire nutrients and protecting against pathogens, according to the paper. The researchers theorize that microbial diversity could help make reefs more resilient to stressors, such as heat waves and pollution, writes Science’s Elizabeth Pennisi.

“The microbes really do run these ecosystems, because they’re involved in so many different kinds of processes,” Deron Burkepile, a marine biologist at the University of California, Santa Barbara, who did not contribute to the research, tells New Scientist’s James Dinneen.

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