A brand-new study on coral bleaching events is currently circulating: according to its findings, as much as 98% of the Great Barrier Reef has already been affected by coral bleaching. While not all corals perish during this process, the proportion of already deceased corals off Australia's east coast was estimated at 40% in 2020. Particularly alarming: thermal stress also leads to a significant reduction in the production of larvae for recolonisation.
There is little that can be done about oceans that have already warmed and undergone acidification. Does this mean we can only watch helplessly? Not entirely.
Thermal events are not uniformly distributed due to weather conditions. According to the authors of the study, there are certain "refugia" where the water generally remains cooler, for instance due to currents or winds. These still intact areas could supply larvae to approximately 58% of the Great Barrier Reef in the future. Furthermore, there is evidence indicating that a small number of corals are capable of relatively rapid genetic adaptation.
In order to relieve already endangered corals, other stressors must be reduced: this includes, for example, population control of coral-eating crown-of-thorns starfish (Acanthaster planci) or algae. Healthy fish and shark populations can therefore contribute to a more resilient coral reef – this requires effective marine protected areas and an end to overfishing. Ultimately, however, it is primarily climate change that must be halted. Only if we can preserve the remaining cool-water refugia do the world's tropical reefs still stand a chance.
Source:
M.W.M. Cheung, K. Hock, W. Skirving, P.J. Mumby: Cumulative bleaching undermines systemic resilience of the Great Barrier Reef. Current Biology (04.11.2021). https://doi.org/10.1016/j.cub.2021.09.078
