Young corals artificially bred using a form of in vitro fertilisation, as opposed to being cloned from fragments of existing corals, displayed significantly greater resistance to bleaching during the fatal heatwave that struck the Caribbean region in 2023, according to a new peer-reviewed study from Florida-based conservation body Secore International.
Secore says that its report represents the first scientific evidence that corals restored using natural reproduction methods prove far more heat-resistant than corals propagated from fragments when subjected to seawater temperatures well above bleaching thresholds.
For the past five years Secore has been running an ambitious programme of laboratory coral-breeding as a way of restoring reefs, an approach that involves training a network of partners throughout and, it hopes, soon beyond the Caribbean region.
“All the effort was worthwhile,” it has now reported. “During the devastating heatwave in the Caribbean in 2023, the young, bred corals out on the reef stayed healthy, while most of the remaining wild corals bleached and many died in the aftermath.”
The method
The customary way of artificially propagating corals was to break a fragment off a source colony in order to grow a new colony as its clone, says Secore. The small coral fragments were grown in nurseries and transplanted onto the reef manually.
The coral seeding approach now being implemented does not create clones. Instead it involves collecting coral spawn from wild corals, and fertilising the eggs and sperm in the lab – or even on a boat or beach – to produce millions of embryos.
The developing coral larvae are grown in ocean enclosures and settled on special substrates to be outplanted onto the reef once they reach a certain size.
Every time a population reproduces, new offspring receive newly mixed sets of genes through recombination – making them distinct from their parent colonies and so enabling adaptation.
Only the young corals produced via breeding exhibit a higher resistance to bleaching compared to adult coral colonies and fragments, says Secore.
Although naturally occurring offspring could perform similarly under elevated temperatures, general failure of reef-building species to recruit in the Caribbean means that few natural offspring occur any more.
First dawn
A Secore team on a routine monitoring dive in Mexico were the first to spot that their out-planted corals appeared to be completely healthy, and their counterparts on Curaçao made a similar observation with a different species soon afterwards.
“Our scientists in Curaçao and Mexico, together with our partner Coralium Lab, gathered data on the health status of several species and cohorts of our outplanted corals,” says Secore research director Dr Margaret Miller. “Then we contacted partners throughout our Caribbean Restoration Network to see how widespread and consistent this pattern was.
“This provided confirmation that assisted recruits of six species of reef-building corals at 15 individual reef-sites in five nations throughout the Caribbean Basin showed the same pattern: young corals bred for restoration are a lot more resistant to bleaching under extreme levels of heat stress than the prevailing corals on the reef.”
“I have been working on breeding corals in the Caribbean over the past 30 years, while simultaneously witnessing tremendous coral loss – due to disease, hurricanes and heatwaves – and the unravelling of the communities that depend on them,” says Dr Miller.
“These results provide a lot of encouragement and confirmation that restoration using assisted coral recruits can play an important role in orchestrating coral persistence into our warmer future. Nonetheless, truly securing the future of coral reefs is absolutely dependent on humankind’s success in controlling global warming.”
Investment pays off
“Our investment over the past five years to build a large network for coral restoration in the Caribbean has paid off,” says Secore founder and executive director Dr Dirk Petersen.
“This network not only produces and outplants tens of thousands of corals every year but could also immediately assess how these corals responded to this unprecedented heatwave. Our priority is now to further scale efforts to the ecosystem level.”
Coral restoration alone won’t cure the reefs in the long term – but it can buy urgently needed time to support coral populations to survive into the next century, says Secore. It is now looking to extend its activities to the Indo-Pacific, and plans to set up a team in Mauritius before the end of 2024 to create an Indian Ocean base.
The study, which covers work carried out off Mexico, Dominican Republic, US Virgin Islands, Bonaire and Curaçao, is published in the journal Plosone.
Also on Divernet: CORAL CRASH: CAN OUR REEFS BE SAVED?, CORAL FARMERS RESHAPING THE FUTURE, WHAT WILL IT TAKE FOR CORAL TO SURVIVE?, 10 WAYS TECH IS RESCUING CORAL
