Corals are subjected to climate change-related impacts worldwide, with overwhelming evidence of mass mortalities affecting vast geographical areas in tropical and temperate seas like the Mediterranean. Although several studies have indicated that repeated exposure to increased water temperature can influence resistance in corals, there is high uncertainty regarding potential adaptive responses. On the other hand, coral survival strategies, hypothetically triggered by adverse environmental conditions, have been reported in fossil corals but remained undiscovered and thus unstudied in extant colonial corals.

This study presents the discovery of such a survival strategy. It is called rejuvenescence and it has been discovered in the Mediterranean coral Cladocora caespitosa. This was the result of monitoring a permanent transect of 246 coral colonies over a time span of 16 years in the Columbretes Islands Marine Reserve (Spain).

The results show the occurrence of this survival strategy, previously only known from extinct fossil corals, associated to the recurrent warming-induced mortalities during marine heat waves. The mechanism, found in 38% of the warming-affected colonies, has allowed near-full recoveries over the studied period and opens a window of opportunity for this coral facing climate change.

However, the authors have serious doubts on the effectiveness of such strategies in a scenario of increased frequency of thermal anomalies, which may outpace the recovery capacity of long-lived corals, and call for urgent action against climate change.

The study also stresses the importance of long-term monitoring to adequately describe the responses of marine organisms and ecosystems to climate change.

https://advances.sciencemag.org/content/5/10/eaax2950

Kersting DK, Linares C (2019) Living evidence of a fossil survival strategy raises hope for warming-affected corals. Science Advances 5: eaax2950.