When corals merge to better survive

This is the story of an encounter that defies the odds: when two young corals of the same species settle in the same place, they can grow together until they merge completely. The appearance of these chimeras natural, very little studied, has long been considered anecdotal.

However, recent research proves that this phenomenon is more common than we think, since it has been observed naturally in many species of coral. According to a study published at the end of July ins BMC Biology within the framework of a Franco-Israeli collaboration, these chimeras are also more resistant than their congeners.

The secret: training to resist

To react to aggression, all living organisms have Genoa response to stress. In chimeric corals, these protective mechanisms are active on a daily basis to respond to stresses due to merger of the two individuals. When external aggressions arise, they are then better prepared. To verify this, the researchers cultivated corals in the Mediterranean.

“ Even under favorable conditions, only 43% of “normal” corals grown at sea survived the first year. For their part, the chimera corals were doing much better since nearly 70% remained alive, explains Jérémie Vidal-Dupiol, researcher Ifremer in the laboratory Host-Pathogen-Environment Interactions.

What about when the environment is less favorable? To study how these protective mechanisms manifest themselves in the face of rapid changes in the environment, the biologists moved corals towards the surface, in warmer and sunnier water. Ordinary individuals must then make an extra effort to acclimatize to these new conditions.

Conversely, since these mechanisms are already activated in chimeras, their resistance to new conditions environmental is immediately more important and effective, which provides them with better protection. In addition to coral, zooxanthellae (micro-algae that live in symbiosis with corals), which are not chimerasare also better protected when they live within a colony of chimera coral.

Chimerism could be one of the natural evolutionary pathways adopted by corals to better adapt to changes induced by climate change. Today, 20% of coral reefs have definitely disappeared and 25% are currently in great danger. It is estimated that another 25% will also be at risk before 2050 if no action is taken.

” These results make it possible to consider new strategies for backup coral reefs, which are home to about a third of marine species known to date. We can proceed by “assisted evolution”that is to say by accompanying these species in their natural evolution, to help them resist changes in their environment”, concludes the scientist.