For the corals found deep in Little Cayman waters, there appears to be relief from heatwaves that threaten reef survival.
A recent article about the coral reefs in Little Cayman, published in the journal Nature, shows there is less coral bleaching and coral mortality found in deeper water. This deep-water environment may provide an important refuge for corals, which are showing increased signs of stress as the sea-surface temperatures rise.
“Over the past several decades, global coral reef ecosystems have experienced a substantial decline in coral cover, with some reefs witnessing reductions from approximately 60 percent to less than 20 percent, largely as a consequence of ocean warming,” the article says.
In summer 2023, a coral bleaching event seriously impacted the corals in the Cayman Islands and around the region, including in Little Cayman, where the Central Caribbean Marine Institute is located.
The director of research at the institute, Gretchen Goodbody-Gringley, is the lead author of the article, published earlier this month, focused on ‘mesophotic reefs’ in Little Cayman.
The ‘mesophotic zone’ is the area between 100 feet and 500 feet below the surface and is characterised by dim, yet significant-enough levels of light for some corals to grow. Below 500 feet, there is not enough light to support photosynthesis, so almost no hard corals exist below that depth.
The researchers in Little Cayman dived to depths of 30 to 150 feet to study the health of the corals. They traversed down the steep and, in some places, vertical drop-offs on the north coast of Little Cayman, hitting dive sights like Randy’s Gazebo, Marilyn’s Cut and Mixing Bowl.
As the scientists headed down the cliff-like face of the underwater landscapes, they identified each coral they came across along the way, and categorised each one by their bleaching status: ‘healthy’ (dark in colour with no visible bleaching), ‘pale’ (lighter than usual and/or exhibiting white blotching), or ‘bleached’ (completely white).
The research showed that while certain corals only tend to inhabit the waters close to the surface, there are some coral species that can survive deeper down and, in this area, where there is less light, the water also tends to stay a little cooler.
The scientific results showed that at increasing depth, there was significantly less bleaching for the following species: lettuce coral, fragile saucer coral, Lamarck’s sheet coral, ridged cactus coral, mustard hill coral, artichoke coral, massive starlet coral and blushing star coral.
“Mesophotic coral ecosystems (like those found in Little Cayman) may provide a thermal refuge for some species of corals,” the findings conclude.
“Given the increasing frequency and intensity of marine heatwaves, understanding the role of deeper reef habitats in mitigating coral loss is critical for informing conservation and management strategies.
“Our study underscores the importance of protecting Mesophotic coral ecosystems as potential thermal refuges.”
There are only about 160 residents on Little Cayman and large parts of the sea around the island are protected. Currently 74.2% of the inshore waters of Little Cayman are designated as marine protected zones.