Coral Seeding: Artificial Insemination Makes Coral More Heat Tolerant

When coral reproduces naturally, it releases large numbers of eggs into the surrounding water. During the process of “coral farming,” researchers collect these eggs, artificially fertilize them, and allow the coral embryos to grow in special containers at the sea’s surface. After just a few weeks, the baby corals are large enough to be released back onto the reef.

Compared to natural coral reproduction, a much larger number of offspring survive through “coral seeding.” “In nature, very few of the eggs released are fertilized, and only a few young corals find a suitable place on the reef. The mortality rate is usually very high,” he explains. Dirk PetersenCoral Conservation Organization Secor International Performs, in conversation with science.ORF.at.

Multiple benefits

According to Peterson, regional impacts such as polluted seawater and rising temperatures are increasingly making it impossible for corals to reproduce naturally. Measures such as “coral farming” could be used to help these reefs and ensure their continued existence.

Researchers working with Petersen have now found another advantage of coral seeding. According to the results of the latest study… StudyingWhich the team now presents in the journal PLOS ONE, this method could also protect coral reefs from widespread bleaching.

Coral bleaching occurs primarily when coral in water gets too hot. “The heat causes stress, causing the corals to reject the algae they normally live with in symbiosis,” says Petersen. Among other things, the algae give corals their vibrant colors. “The corals can survive in this bleached state for a few weeks. But if they can’t repopulate their tissues with algae, they will die.”

Heat tolerant offspring

In the summer of 2023, strong heat waves occurred in many parts of the world, which also affected coral reefs. The Caribbean and Gulf of Mexico were particularly affected. “The summer of 2023 was very dramatic. A lot of coral reefs in Florida and the Caribbean were bleached and died, and entire reefs were lost,” says Petersen.

During this time, the research team observed several corals and realized that the young corals that had been released earlier as part of the coral transplantation were not bleached. “The young corals were healthy, while many other corals in their area had died,” Petersen explains. The research team then collected data from five countries on six different coral species, and were able to show that the young corals in all five countries were significantly more heat tolerant.

Early age is crucial.

It’s not yet clear why the artificially fertilized coral offspring coped better with the heat. Basically, corals aren’t anything special—so Petersen suspects that the heat tolerance was primarily linked to the corals’ young age. “We know from young corals that they can absorb many different strains of unicellular algae, which makes this algae-coral symbiosis more stable even at higher temperatures—that is, the coral becomes more resilient.” The corals the team examined lived in symbiosis with such algae in all five countries.

However, as corals age, they lose their resilience again – and according to Petersen, a way is needed to keep the number of young corals on the reef at a consistently high level. The next goal for Petersen and SECORE International is to make “coral farming” more effective and scale it up. “For example, we already allow corals to grow on substrates that allow them to attach to the reef. This means that in the future we simply want to distribute the coral offspring in large quantities from the boat out to sea in order to settle as many young corals on the reef as possible.

Reducing emissions is essential.

This is essential for the future health of coral reefs – the more young corals that live on the reef, the more likely it is that many of them will survive future heatwaves. Measures such as “coral farming” can help, says Petersen, “but it’s not a magic bullet.” In addition to artificial breeding, regional measures are also needed, for example to improve water quality in some areas.

The most important action is again to drastically reduce global greenhouse gas emissions. This is the only way to avoid future heat stress on coral reefs and ensure the long-term survival of our colorful coral reefs.