LC reefs may fare better in face of bleaching event

(CNS): As coral reefs around the world, including those in Cayman Islands waters, face another bleaching threat this year, scientists at the Central Caribbean Marine Institute believe the reefs around Little Cayman may prove more resilient than others in the region because they are healthier and face fewer stressors than other reefs.

Following last summer’s long and extreme marine heatwave, the reefs monitored by CCMI were badly bleached, and almost half the corals ultimately died. But key reef-building species showed lower mortality and higher rates of recovery, which may help protect the coral this summer as sea temperatures in the region continue to climb.

According to the CCMI’s 2023 Coral Bleaching Report Card, bleaching off Little Cayman was severe. The summer of 2023 was the most drastic marine heatwave on record for Little Cayman, three times more intense than any previous heatwave. The island experienced 17 degree heating weeks from July to December.

Researchers found that 90% of corals in Little Cayman bleached during that marine heatwave, and over 50% subsequently died, most of which were ‘weedy’ species. This was attributed in part to higher coral cover to start with and the presence of more susceptible species that are not present on most reefs with more stressors.

However, because the reefs around Little Cayman are protected from the added pressures of local threats such as pollution and overfishing, they have shown better long-term recovery. Before the bleaching event, coral cover in Little Cayman was about 20%, compared to 10-15% regionally. CCMI’s pre-bleaching monitoring showed that 90% of the reefs were in good to very good condition.

“This higher coral cover, along with higher species diversity and healthy fish populations, particularly herbivores, may mean that Little Cayman’s reefs show better long-term recovery than reefs in poorer health. This provides hope for the recovery of these reefs, but the next year or so will be pivotal,” the CCMI’s scientists said in a release about the reef report.

CCMI said that data it has accumulated over the last 25 years shows the above-average health of corals in Little Cayman, with no reefs recorded in poor health in 2022 or 2023 and stable levels of coral cover despite the regional decline. “No one can say for certain how these reefs will recover and fare in the future as climate change impacts intensify; we can say that historically they have shown stability while other reefs in the Caribbean have recorded decline,” the researchers said.

The impact of last year’s coral bleaching was extreme, not only in Little Cayman but globally, and the summer of 2024 is likely to bring further bleaching. The historically stable, healthy and highly diverse reefs
in Little Cayman may fare better when it comes to recovery and become a site of hope and re-seeding for other reefs. But with the impact of climate change, these reefs need help more than ever. Therefore, CCMI’s researchers are seeking solutions to support reef recovery and help the reefs survive and adapt through science-based action.

“CCMI is taking a multi-faceted approach to helping reefs to survive and adapt to climate change through a combination of cutting-edge research and action,” the release stated. “CCMI has been pioneering a resilience-based coral restoration programme in Little Cayman since 2012. This restoration programme has grown over 1,500 corals outplanted over 70 square metres of coral onto the reefs of Little Cayman, informed by CCMI’s ongoing research in coral genetics to boost the resilience of corals to stressors such as warmer oceans and coral disease.”

The research facility is also researching how coral ecosystems deeper than 30m (mesophotic reefs) can help shallow-water corals survive climate change. With National Science Foundation funding, CCMI’s researchers are investigating how corals may adapt to extreme environmental conditions. A recent publication by CCMI’s Director of Research, Dr Goodbody-Gringley, found that coral larvae from shallow-water reefs may be able to settle and survive on deeper reefs, offering hope that these mesophotic reefs could provide refuge for corals if shallow reefs become inhospitable.

CCMI has been exploring and documenting previously uncharted mesophotic reefs on seamounts Pickle Bank and 12-Mile Bank off the coast of Cayman. Technical divers have found highly productive coral reefs that could provide further hope for maintaining coral biodiversity through climate extremes.

Last year, Little Cayman was placed on the UK’s wish list for UNESCO status, which would give it the protection that is desperately needed if the resilience of the reefs is to be maintained. While development to date on Little Cayman has been held at bay, it remains in the crosshairs of those looking to profit from its beauty.

Plans for a new and bigger airport on the island, which is not widely supported, could significantly change the island by bringing in more visitors, which would encourage more residents, resulting in more stress on the marine environment.

If the Cabinet is successful in steering controversial amendments to the National Conservation Act through parliament, it might be able to avoid having to conduct an environmental impact assessment for the project, putting the last remaining areas of resilient reef in Cayman under further threat.

See the full report here.