Record temperatures recorded in the oceans due to climate change are killing coral reefs across the world, a phenomenon called bleaching, and initiatives to try to restore these essential marine ecosystems are increasing in an attempt to save them.
– How to replenish the coral? –
The first possibility is to detach coral fragments from a healthy reef. They are then broken into smaller pieces in a process called micro-fragmentation. Each of these fragments can then become a new coral.
Another option is to collect pieces of coral detached naturally, for example during a storm, so-called corals of opportunity.
Conservationists also resort to the more complex egg collection. Coral reproduction, called spawning, usually occurs once a year. Entire reef colonies then release their eggs at the same time.
Many factors come into play, such as the phases of the Moon or the temperature of the waters.
– And after? –
Coral fragments are kept in nurseries until they become strong enough to be transplanted to a natural or artificial reef.
The same goes for opportunity corals in the event that they are not yet strong enough to be attached directly to a reef.
The eggs and sperm extracts collected during coral spawning are transformed into larvae, integrated into natural or artificial formations during their development.
– What corals are used? –
Branched corals are generally those used. Their fragile branches are more likely to become corals of opportunity and are also easier to micro-fragment, unlike other corals.
Their ability to grow very quickly provides restoration projects with rapid results.
But restoring just one type of coral can lead to a reduction in ecosystem diversity.
– Does it work? –
Survival rates after restoration are between 60 and 70 percent, according to a study published in 2020.
However, almost half of the projects analyzed by this study failed to clearly determine whether they had achieved their original objectives, including achieving coral reef function itself.
Monitoring of these projects is often brief: less than a year in half of the cases, much less than the time required for the formation of a reef.
However, a recent study presents encouraging results. Carried out on artificial reefs in Indonesia, the study revealed that in four years, the reconstituted coral emitted as much carbon as that of a natural reef.
– What are the other factors? –
Some experts worry that coral restoration is too often presented as a panacea.
They emphasize that these transplants will only survive if environmental conditions are favorable.
According to them, climate change, which is responsible for the extreme temperatures causing coral bleaching, must be tackled as a priority.
“Well-designed and well-led restoration projects have an important role to play, but they can only do so much if radical climate action is not taken” immediately, warns Lisa Bostrom-Einarsson, the marine biologist who led the 2020 study.
Explosive fishing and sedimentation, stress factors for coral, must also be combatted to save coral reefs.
The Indonesian study showed that few “natural corals” had developed around the transplanted corals.
Building reefs by micro-fragmentation also limits genetic diversity, which can put the formations at risk in the event of an outbreak of disease.
“Restoration will not save the corals at the current rate at which we are losing them,” said Gavin Miller, a marine scientist with the Global Reef organization in Thailand.
