Coral reefs, bastions of marine biodiversity because of the abundant fish, invertebrates, and algae they support, are also home to Earth’s greatest microbial diversity, according to a new estimate.
From 2016 to 2018, an international team of researchers aboard the sailing ship Tara studied 99 reefs off 32 islands across the Pacific Ocean, home to 80% of the world’s corals. They sequenced DNA from more than 5000 samples of three coral species, two fish species, and plankton. The team identified a half-billion kinds of microbes, mostly bacteria. Microbes were most diverse among the plankton; among animals, the blade fire coral (Millepora platyphylla) and Moorish idol (Zanclus cornutus) had the most types, the team reports today in Nature Communications.
When the researchers extrapolated those findings to estimate the total reef microbial diversity across the Pacific, it was equivalent to Earth’s total, previously estimated microbial diversity. The team members don’t know what leads to the great bacterial diversity, as it didn’t align with the greater diversity found in corals of the western Pacific. Nor did the microbial diversity correlate with seawater temperature. (During their research voyage, the scientists also measured temperature, salinity, and other environmental conditions.)
The researchers have yet to fully analyze these data, but they expect this high microbial diversity can help the reefs be more resilient in the face of heat waves, pollution, turbidity, and other stressors, acting as ecological insurance. Some bacteria on coral provide benefits—such as supplying vitamin B to their hosts—and their diversity suggests that at least some helpful microbes are likely to survive a particular environmental insult and can continue to support the coral.
