‘Coral seeding’ increases resistance to extreme heatwaves

SECORE International has developed a coral seeding method that utilizes assisted reproduction – breeding corals to help restore reefs. This approach has been implemented across the Caribbean through a network of training and partners. 

A recent study confirms that the coral seeding method is making a significant impact: during the severe 2023 heatwave in the Caribbean, young corals that were bred through SECORE’s efforts remained healthy, while many wild corals bleached and died.

Coral seeding in the Caribbean 

The summer of 2023 brought devastation to many coral reefs in the Caribbean Basin. An unprecedented heatwave, both in intensity and duration, hit the region, leading to widespread coral bleaching. 

With high seawater temperatures persisting, many corals were unable to recover and perished. 

However, during this time of crisis, a hopeful discovery was made by SECORE’s Restoration Coordinator in Mexico, Sandra Mendoza Quiroz. 

While conducting a routine dive to monitor their outplanted corals, she found that the young corals they had bred were healthy, standing out among the bleached and dying reefs. 

Assisted reproduction and coral survival

Similar findings were reported by SECORE’s team in Curaçao, where another species of bred coral had withstood the heat.

“We were excited to observe this pattern showing another benefit of using assisted coral recruits in restoration,” said Margaret Miller, research director of SECORE.

The team in Curaçao and Mexico, working with Coralium Lab at the Universidad Nacional Autónoma de México, collected data on the health of various species and groups of outplanted corals. 

The experts reached out to partners across their Caribbean Restoration Network, including the Dominican Foundation for Marine Studies, the Nature Conservancy in the Caribbean, and Reef Renewal Foundation Bonaire. 

Together, the researchers confirmed that young corals bred for restoration were significantly more resistant to bleaching compared to their wild counterparts across six coral species at 15 reef sites in five different Caribbean nations.

Coral seeding builds resilience 

This study marks the first scientific evidence that corals restored using natural reproduction methods demonstrate greater resistance to extreme sea temperatures than wild or fragmented corals.

Miller, who has been breeding corals in the Caribbean for over 30 years, expressed optimism about the findings. 

“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,” said Miller. 

“Nonetheless, truly securing the future of coral reefs is absolutely dependent on humankind’s success in controlling global warming.”

Producing millions of coral embryos 

Coral restoration methods have evolved significantly in the past decade. Traditionally, corals were propagated by breaking fragments off source colonies and growing them in nurseries before manually transplanting them onto the reef. 

Today, SECORE’s coral seeding approach, which breeds corals specifically for restoration, is widely implemented throughout the Caribbean. 

This method involves collecting coral spawn from wild corals, fertilizing the eggs and sperm in a controlled environment (either on a boat or beach), and producing millions of coral embryos. 

The coral larvae are grown in ocean enclosures and settled on special substrates before being outplanted onto the reef.

Each generation of corals that reproduces naturally receives a new combination of genes, enhancing their ability to adapt. 

Importance of the new breeding efforts

The study revealed that the young corals produced through breeding showed greater resistance to bleaching than adult coral colonies and fragments. 

However, due to the recruitment failure of many reef-building species in the Caribbean, natural offspring are rare, which further underscores the importance of SECORE’s breeding efforts.

Dirk Petersen, the founder of  SECORE, is thrilled with the study’s positive results. 

“Our coral seeding approach is an important contribution to help coral reefs deal with climate change,” said Petersen. “Our investment over the past five years to build a large network for coral restoration in the Caribbean has paid off.” 

“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.”

A chance for coral reefs to survive

Coral restoration, however, is not a solo endeavor. It requires collaboration across various disciplines, from science and engineering to on-the-ground implementation. 

The process involves logistics, effectiveness, and thorough training, and must be grounded in strong management strategies that engage local communities. 

While coral restoration is crucial, it alone cannot solve the broader challenges posed by climate change. Still, it provides vital time to help coral populations survive in the face of environmental pressures.

“Our Caribbean Training and Capacity Building Program has turned out to be a successful model, which we urgently need to take to other regions across the world,” Petersen said. 

In his view, as extreme weather events continue to increase in frequency and severity, regions beyond the Caribbean will also be affected. 

“Restoration measures are best implemented at an early stage to strengthen the reefs. Once degradation has reached a critical level, restoration becomes much more challenging,” said Petersen.

Expanding coral restoration efforts

SECORE is now expanding its efforts globally. In 2023, the organization hosted its first training session for participants from U.S. jurisdictions in the Western Pacific and plans to establish a team in Mauritius by the end of the year. 

This new base will serve as a hub for restoration training in the Indian Ocean. “Restoration truly is a cooperative effort – let’s all work together to give these valuable ecosystems a future!” Peterson concluded.

The study is published in the journal PLoS ONE.

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