Coral bleaching on Little Cayman

Scientists have found evidence of widespread bleaching of Little Cayman’s coral reefs less than a month after finding massive bleaching of the reefs in Grand Cayman.

Example of bleached coral

Example of bleached coral
Photo: NOAA

The scientists at the Central Caribbean Marine Institute, assisted by local Department of Environment officials, visited several dive sites around Little Cayman last week.

‘Coral bleaching can be caused by a number of different stressors, but the most common stressor is unusually warm water temperatures,’ said Brenda Gadd, managing director of CCMI.

The Department of Environment reported massive coral bleaching last month on Grand Cayman.

Following reports from the diving community and a ‘bleaching potential’ alert from the recently installed ICON weather monitoring station in Little Cayman, DoE staff conducted assessed the reefs on the north, west and south coasts of Grand Cayman last month.

They found nearly all corals in the shallow reefs to about 30 ft showed signs of moderate to severe bleaching, while approximately 80 per cent of corals in the deeper reefs to 120 ft exhibited the early signs of coral bleaching.

‘If the stress causing the bleaching, assumed to be high temperature, is removed soon and the corals are not too weakened, it’s possible that they will recover their algae and survive intact,’ said Dr. Marilyn Brandt of the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

‘However, if the stress continues, the corals may starve or become more susceptible to infections and disease, which could result in significant mortality rates. Therefore, care should be taken to avoid touching or damaging the corals at this time, so that they have the best chance of survival.’

Coral bleaching is the loss of a coral’s symbiotic algae population that lives in its tissues. These microscopic algae provide the coral with extra nutrients that help the coral to grow and reproduce. They also give corals their bright and myriad colors.

When the algae are lost due to stress, the coral tissue becomes transparent and the coral’s skeleton can be seen through the tissue, making the coral appear bright white, hence the term ‘bleaching.’

The CCMI Little Cayman Research Centre scientists visited five sites last week to observe the bleaching, including Sailfin Reef, Rock Bottom Wall, Snapshot Reef, Nancy’s Cup of Tea, and Grundy’s Gardens.

They observed bleaching at every site, and found it was affecting corals as shallow as 20 feet and as deep as at least 120 ft on Bloody Bay Wall.

Many different species of corals were affected, including gorgonians. Using transects to quantify the amount of bleaching, it was found that up to 96 per cent of coral cover on Little Cayman reefs was either totally bleached or extremely pale compared to normal coloration.

Expedited permission was granted by the DOE to extract small samples, in order to identify the remaining types of algae that the corals are hosting in their tissues.

Since some algae types have been found to be more resistant to thermal stress, identifying whether corals are hosting these more resistant types could help scientists better understand the distribution of bleaching that we are seeing throughout the Cayman Islands.

At the time of the observations, no mortality associated with bleaching was observed.