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When a significant coral bleaching event swept across the reefs of Mauritius last summer, one small group of corals remained as vibrant as ever.
While neighboring wild reefs experienced bleaching rates as high as 80%, Dr. Nadeem Nazurally’s reefs experienced just as much, and often more, in survival rates
Nazurally is naturally breeding heat-resistant corals to resist just such events, and the first major acid test shows that such coral management methods hold real potential for protecting these vibrant marine ecosystems for decades to come.
The island nation of Mauritius, off Africa’s east coast, is home to nearly 250 coral and hydrozoan species. The reefs they form anchor the livelihoods of both humans and fish, supporting fisheries that produce to the tune of billions, and act as home for one-fourth of all Mauritius’ sea life.
Since 1998 when the islands recorded their first coral bleaching, the reefs have been thusly cooked on 4 more occasions, the most recent being last summer when water temperatures reached 88°F. Previous bleaching events gradually revealed that regular coral restoration strategies—of cloning from cut offs of robust individual colonies—was no longer viable.
With the government and the UN subsidizing restoration efforts, new methods were needed. Organizations like the Mauritius Oceanography Institute, and the University of Mauritius, and Odysseo Oceanarium, now work to advance the science of heat-resistant coral breeding, and Nazurally’s success seen last summer is a testament to the progress the country’s marine science community has made.
The science of coral breeding has come a long way in the last decade. Corals being animals, they reproduce much like other marine invertebrates: exogenously—but in a way that is extremely difficult to predict, since it’s done in perfect synchronicity across entire reefs, often in single evenings and lasting for just hours.
Odysseo has leveraged advancements made worldwide in the science of predicting spawning events to create a program of timing coral reproduction and collecting eggs and sperm from the corals by boat.
These are then used to breed corals in protected nurseries, with those coral phenotypes that survive in warmer water being selected to reproduce.
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A study published by Dr. Nazurally in the summer showed that the hydrozoan genus (similar to coral) Millepora, when bred in this way, showed a 99.8% survival rate during the bleaching, compared to an 88% average rate across all coral genera, and a 10% survival rate for corals bred with previous methods and without a focus on heat-resistance.
The study also examined the differences in how coral grew when cultivated on a floating platform midway down the water depth, and when grown on the seabed. The results suggested that in areas of high development that are popular with tourists, floating platforms protect the corals from damaging sedimentation, while less frequented zones would merit a seabed nursery approach.
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