DNA testing reveals hidden coral diversity

A new study has revealed “cryptic species” of coral that appear identical to each other but are genetically distinct and have different ecological roles, raising questions over the best way to protect them.

James Cook University’s Dr Ira Cooke was part of the international team behind the study, published today in the journal Current Biology, that examined serpent coral, (Pachyseris speciosa), one of the most ubiquitous corals in the Indo-Pacific.

“Tens of thousands of multicellular species have been identified in association with tropical coral reefs, but it’s thought that is less than 10 per cent of the actual species out there. Reef-building corals were considered to be relatively well mapped in species terms, but it was surprising that there were less than 850 valid species identified worldwide,” said Dr Cooke.

“We know we are greatly underestimating the true number of coral species because of hidden diversity,” said lead author Dr Pim Bongaerts of the California Academy of Sciences.

“We put the serpent coral specimens through a comprehensive genomic and phenotypic assessment. We found that while all the specimens from the Great Barrier Reef were visually indistinguishable, there were in fact three different species,” said Dr Bongaerts.

“We call these cryptic species because they are essentially hiding in plain sight,” said Dr Cooke.

“It’s impossible to tell these corals apart with the naked eye, but genome sequences tell a very different story – that these are distinct lineages that go back millions of years.”

He said that while finding “cryptic species” like this was nothing new, the team showed that it is important because the corals have different ecological characteristics.

Using remotely-operated vehicles and specialised deep diving gear, the researchers investigated corals from shallow depths down to 80 metres beneath the surface in the vastly understudied mesophotic zone of coral reefs.

They discovered that although individuals from each species could be found over the entire range of depths, they had distinct depths where they were most abundant, with corresponding differences in physiological traits such as protein content that affect their ability to survive and thrive at their preferred depths.

“Knowing what corals thrive where and at which depths is crucial for reef conservation,” says study co-author Professor Ove Hoegh-Guldberg at The University of Queensland.

“Most marine protected areas only protect shallow reefs, so when there are hidden species that are more abundant at mesophotic depths it represents diversity that is being overlooked by current conservation strategies.”

Ultimately, the researchers hope that their findings reveal the importance of taking a holistic look at hidden species that appear identical, but may have differences that impact global conservation efforts.

“Understanding what species there are and what they contribute to the reef ecosystem is the bedrock of good reef management,” Dr Cooke said.

“It’s critical to start capturing both genetic and ecological aspects of hidden diversity to improve our understanding and ability to protect these fragile ecosystems.”

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