WILLEMSTAD - The Caribbean Research & Management of Biodiversity (CARMABI) Foundation reports that young coral, cultivated from wild-caught gametes (reproductive material of corals), did not bleach despite the unprecedented and prolonged heatwave that hit Curaçao this year. In other parts of the Caribbean, this heatwave caused a significant loss of corals in many species, and in Curaçao, the situation is closely monitored with a considerable number of corals currently showing advanced signs of bleaching.
Now that the seawater temperature has been below the bleaching threshold since late November, CARMABI is hopeful that many corals experiencing heat stress will soon recover their symbiotic algae from the surrounding waters and survive this extremely stressful period, but only time will tell.
Meanwhile, scientists from SECORE International, CARMABI's partner specializing in coral reef restoration, conducted research to monitor the health of young brain corals, which they have been cultivating from coral reproductive material in recent years. Surprisingly, the young brain corals, between 1 and 4 years old, show no signs of bleaching, while many adult colonies in their vicinity have lost their symbiotic algae, putting them at risk of starvation. These observations came shortly after similar reports from SECORE colleagues in Mexico who witnessed laboratory-cultivated staghorn corals withstand extreme temperatures, while many adults of the same species bleached and died.
So far, reports have been received for a total of five coral species that show a similar pattern at various locations: Curaçao, Mexico, the Dominican Republic, and Cuba. SECORE and partners are currently collecting and analyzing data from these and multiple locations to quantify the significance of this pattern.
Since 2010, SECORE has been closely collaborating with CARMABI to enhance coral breeding and restoration techniques that rely on the sexual reproduction of corals. Every year between August and October, corals reproduce by releasing their gametes (egg and sperm cells) into the seawater during 'coral spawning events.' Over the past decades, CARMABI and SECORE scientists have pioneered methods to cultivate baby corals from gametes harvested during the breeding season. Each time gametes from different colonies are collected and mixed, hundreds of thousands of genetically unique coral offspring are created. This genetic diversity is crucial: the more diversity, the greater the chance that some individuals have inherited traits enabling them to withstand prevailing conditions. These new corals are then replanted on the reef to help replenish future coral.
The fact that these young corals do not bleach as severely as the adult corals is very encouraging. How these young corals can achieve this is unclear: perhaps they have genetic material that allows them to better adapt to heat stress, or maybe their small size gives them an advantage in coping with high temperatures. In any case, these observations highlight the fact that young and small corals are not always the most vulnerable and underscore the importance of coral reef research and restoration to aid in the recovery of endangered coral populations.
Photo: A 3-year-old brain coral, cultivated from larvae by SECORE and showing no signs of heat stress. This young coral is currently growing on the reef in Piscadera Bay.
(photo: Dr. Valérie Chamberland)
An adult brain coral colony suffering from heat stress. Symbiotic algae found in the coral tissue normally provide their host (the coral) with food through photosynthesis, but they begin to produce toxins when the seawater warms above 29 degrees Celsius, forcing the coral to expel them. Since these algae give corals their typical green/brown color, corals appear to bleach when the algae are expelled. The coral tissue itself is transparent, revealing the underlying white skeleton. Hence, this phenomenon is called 'coral bleaching' in English.