LC reefs show resilience

Coral reefs around Little Cayman have almost completely recovered from a 2005 ocean warming event that caused the most extreme coral bleaching and mortality ever seen in the wider Caribbean.

Marine scientists at the Central Caribbean Marine Institute’s Little Cayman Research Center carried out a survey of reefs around Little Cayman in January.

While the bleaching that was recorded in 2005 – the hottest year on record in the Northern Hemisphere – was the worst ever seen in the Cayman Islands, reefs in Little Cayman have come back stronger than most other Caribbean reefs, they say.

According to a report published by the Global Coral Reef Monitoring Network in January, other reefs in the region have not fared so well. The US Virgin Islands lost over 50 per cent of coral reef cover; Barbados experienced 17 per cent to 20 per cent coral mortality; losses in the French West Indies ranged between 11 per cent and 30 per cent; while sites in the Dominican Republic suffered up to 38 per cent mortality.

‘The reefs are regenerating at a high level,’ said CCMI President Ms Carrie Manfrino. ‘This is very good news and illustrates a level of resilience in Cayman that is not common on Caribbean reefs.’

Ms Manfrino said the resilience of Little Cayman’s reefs is probably a reflection of the fact that they are subject to less human induced stresses than reefs in more populated and industrialized areas, and are therefore better able to respond to threats like the 2005 bleaching event.

It is not yet clear whether reefs around Grand Cayman proved as resilient, although the CCMI plans to conduct surveys around the Island in the coming months.

Ms Manfrino is guessing the health of Grand Cayman’s reefs will vary across locations, with reefs in less populous areas proving more robust than reefs closer to George Town, where human induced stresses are higher.

‘At East End I would expect to see a gorgeous reef, but closer to town, I would expect to see a more degraded reef,’ she said.

For many Caribbean reefs, barriers to coral regeneration include over fishing and high amounts of nutrient spilling into the ocean from run-off and sewage. That nutrient contributes to fleshy algae growth on reefs, making it difficult for coral larvae to settle. Over fishing means there are not enough fish to eat the algae away.

‘Low nutrient input from runoff and sewage and healthy fish populations are key to maintaining healthy corals,’ said Ms Manfrino. ‘Clues to resiliency in the reefs of Cayman may be found in herbivorous fish populations, which appear to be stable around Little Cayman,’ she said.

Ocean thermostat?

There could also be other factors at play. Earlier this month, researchers in Australia and the USA identified the existence of a naturally occurring ocean thermostat, which seem to be preventing an area in the western Pacific ocean from heating beyond a particular point.

The study has some scientists hoping the phenomena cold help protect some coral reefs from the impacts of climate change.

The research was led by the National Centre for Atmospheric Research’s Ms Joan Kleypas, who attended a CCMI-NOAA think tank hosted at the Little Cayman Research Centre in December.

The scientists studied the Western Pacific Warm Pool, a biologically diverse area of coral reefs northeast of Australia, where naturally warm sea-surface temperatures have not changed much in recent decades, despite rising sea-temperatures in other regions.

The stable ocean temperatures mean reefs in the region have mostly avoided bleaching episodes. The researchers said their finding give weight to a much contested theory that naturally occurring processes prevent sea surface temperatures rising above about 88°F.

In the Cayman Islands, sea-surface temperatures range from around 84F to 88F.

While Cayman did record ocean surface temperature rises in 2005, they were not of the magnitude experienced by close neighbours including Cuba and Jamaica, Ms Manfrino said. But it is not clear whether an ocean thermostat type phenomenon was behind that, she said.

‘I think we need to re-examine the data in light of these findings but, yes, it’s a possibility.’

Commenting on the Western Pacific Warm Pool, Ms Kleypas said, ‘Global warming is damaging many corals, but it appears to be bypassing certain reefs that support some of the greatest diversity of life on the planet.

‘In essence, reefs that are already in hot water may be more protected from warming than reefs that are not,’ she said.

‘This is some rare hopeful news for these important ecosystems.’

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