UH scientists study whether blue coral’s ‘secret’ sunscreen may save reefs

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Credit: Mike Henley, SI/ HIMB

HONOLULU (KHON2) — The Hawaiian blue rice coral may reveal important clues as to how some corals might weather climate change, according to scientists from the University of Hawaii at Manoa and the Smithsonian Institute.

Those clues lie in the protein produced by the coral that not only imparts its deep blue color, but also acts as a natural sunscreen.

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Coral reproduce by releasing eggs and sperm into the water column. As climate changes and the ocean warms, coral become stressed, potentially affecting their ability to reproduce and sustain healthy reefs.

If coral cannot reproduce, the researchers say they cannot adapt to changing conditions in oceans.

With the UH Manoa’s Hawaii Institute of Marine Biology (HIMB) as their research base, the Smithsonian team conducted long-term monitoring on coral reproduction of two coral species in Kaneohe Bay. 

The scientists hypothesized that the same sunscreen filters out harmful ultraviolet (UV) radiation that may be detrimental to coral reproduction.

They found that after the consecutive large-scale bleaching events in 2014 and 2015, sperm motility fell in the monitored species by almost 50%. However, later studies determined that the blue rice coral seemed immune to these reproductive changes. Specifically, the blue rice coral had sperm motility typically above 90%, while their partner species, the brown rice coral, had half the amount. They did not know how to explain these large differences, but contemplated whether the clues may reside in the coral’s color.

“We had studied the brown rice coral for several years and witnessed in real time their decline due to bleaching in 2014 and 2015,” said PhD candidate at HIMB, Mike Henley, who is lead author of the study. “The blue rice coral is often overlooked, and its sperm motility wowed us the very first time we saw it. While the brown rice coral lagged behind in recovery from bleaching, the blue rice coral either recovered really quickly, or perhaps it was never impacted at all. Hopefully, this work will reveal clues to help other corals weather climate change and ocean warming.”

Coral color is produced largely by their internal algae, giving many species in Hawaii a brownish appearance. These algae also produce sunscreen for the coral. However, when the oceans warm, the algae are expelled, and corals appear bleached. When the algae leave, the sunscreen goes along with them, leaving the coral vulnerable to harmful UV radiation.

In contrast, the blue rice coral produce their own sunscreen and might retain protection from UV radiation, even after their internal algae leave during bleaching.

The team suggested that the brown rice coral may suffer long-term damage to their reproductive stem cells during the bleaching event when the sunscreen is absent.

To read the full study, click here.

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