Cool seas help LC corals recover from bleaching

Bleached Elkhorn coral, photo courtesy CCMI

(CNS): Corals on the reefs around Little Cayman appear to be bouncing back, according to scientists on the island, who were on high alert for a possible mass mortality of corals due to bleaching last summer. Although some 60% of the corals around the island were impacted by the high water temperatures from June to October, the Central Caribbean Marine Institute has reported significant signs of recovery after temperatures began falling in November. 

According to CCMI, scientists had predicted that 2015 would be the third global bleaching event on record. Corals were expected to bleach and perhaps experience mass mortality near the end of the summer as seawater temperatures exceeded the thermal tolerance levels for most coral species.

As corals bleach, they pale and may turn white, which makes colour a good proxy for stress levels. CCMI, a non-profit marine research organisation based on Little Cayman, adapted a rapid response protocol using coral health charts with colour scales similar to paint samples found in home improvement stores. Snorkelers and divers, including undergraduate students and citizen scientists, assisted in collecting data and photos, CCMI said in a release.

Between June and September 2015, when seawater temperatures increased to 30-31°C, approximately 25% of Little Cayman’s corals turned pale or bleached white. By October, when the ocean reached its maximum summer temperature, almost 60% of the surveyed corals had changed colour. Fortunately, storms and high winds brought relief to the reef.  Seawater temperatures dropped below critical levels and by November, colour was returning to the reef.

“The good news is that most of the Little Cayman corals appear to be recovering after the elevated temperatures they experienced in 2015.  CCMI will continue its surveys to record whether the corals experience any long term impacts of the bleaching event,” the release stated.

Funding from the Edmund F. and Virginia B. Ball Foundation enabled CCMI to monitor Little Cayman reefs before, during and after the extreme temperature event.

Dr Carrie Manfrino, CEO of CCMI, said, “Worldwide, coral reefs are in danger from rising sea temperatures in a variety of ways. Being able to closely monitor any sudden or gradual changes to coral’s natural environment allows us to identify how exactly they are affected and to take measures to protect and in the future regenerate the most resistant corals. Without funding from generous organisations, such as the Ball Foundation, this type of work would not be taking place.”