Extent of hurricane damage to Caribbean coral reefs revealed by scientists

Early investigations of coral reefs in the US Virgin Islands have revealed severe damage resulting from hurricanes Maria and Irma, which struck the region this year.

The impact of the hurricanes that tore through the Caribbean in 2017 was clear, but less obvious were the devastating consequences for underwater environments.

Reefs provide habitats for many fish and other creatures, meaning understanding their recovery following natural disasters is vital.

To investigate how vulnerable corals are to hurricanes, and how capable they are of recovering, a team of scientists has been exploring the reefs off the island of St John.

"In shallow waters, what we found certainly lived up to our expectations – holy moly this was bad news," said expedition leader Dr Peter Edmunds, a biologist at California State University, Northridge.

In some places coral colonies had branches ripped off and “open wounds” in which harmful bacteria and algae were growing.

Elsewhere, entire colonies had been swept away by the storms.

"Hurricanes generate huge waves. The effect is like sandblasting – the waves carry sand and debris, such as bits of broken coral, onto the reefs, striking them over and over again," said Dr Howard Lasker, a geologist at the University at Buffalo.

In deeper reefs off St John, the scientists found the picture was “more nuanced”.

There were less immediate signs of devastation, but closer inspection revealed more displaced and damaged corals.

The scientists intend to continue visiting the same sites to monitor reef recovery, learning from the harm caused by hurricanes Maria and Irma.

"It's an interesting natural experiment," said Dr Lasker. "You could not, in good conscience, conduct such an experiment on your own as a scientist, and it is sad to see these beautiful places in the ocean damaged so severely.”

“But we can learn from this – it gives us the chance to better understand the process of recovery," he said.

They note that while they saw promising signs off St John, coral reefs today must deal with additional factors that could make recovery difficult.

Hurricanes have always occurred in the Caribbean, so the region’s habitats should be able to come back from the brink of destruction, just as forests recover following naturally occurring wildfires.

However, climate change is putting additional strain on these habitats by increasing the likelihood of catastrophic bleaching events like those seen in the Great Barrier Reef.

Furthermore, scientists are confident the frequency and severity of natural disasters like the hurricanes that struck the Caribbean this year are being affected by climate change.

This makes it crucial that teams like the one led by Dr Edmunds monitor the extent to which coral recovers from hurricane-induced damage.

A Unesco scientific assessment this year predicted world heritage reefs are likely to disappear by the end of the century, but Dr Edmunds has a slightly more optimistic outlook for St John’s coral.

"I don't see signs that they are going to disappear,” he said.

“They will persist, but in what form?"