Scientists at the Smithsonian Conservation Biology Institute are taking another step to understand why some corals may resist climate change better than others, and the secret may lie in a specific protein that produces natural sunscreen. As the name suggests, Hawaiian Blue Rice Corals sport a deep blue pigment, which is created by the chromoprotein and filters out harmful ultraviolet (UV) rays from the sun. Although UV damage can have long-term effects on the reproduction of many species of coral, including brown rice coral, it may not have the same effect on blue rice coral. The results of this study were published on June 9 in the article “Reproductive plasticity of Hawaiian Montipora corals following thermal stress” in Scientific reports.
“Having witnessed the devastating effects of bleaching on brown rice coral in 2014 and 2015, it is encouraging to see blue rice coral recovering quickly after bleaching or not having been affected at all by high ocean temperatures Said Mike Henley, Smithsonian Conservation Biology Scientific Institute and lead author of the article. “By studying the reproductive successes of blue rice corals, we can better understand how other corals resist climate change and warming oceans.”
The color of a coral is derived from a microscopic protozoan called a zooxanthellae. This algae lives inside coral tissue and serves as the primary food source for shallow and reef-building corals, including brown rice coral and blue rice coral. They have a symbiotic relationship; the coral protects the zooxanthellae, and the zooxanthellae in turn provide food for the coral. These algae also produce sunscreen for the coral. Corals are animals and cannot photosynthesize, but zooxanthellae can. The waste products of their photosynthesis are the sugars that nourish the coral.
However, when ocean temperatures warm, the corals become stressed and the symbiosis is broken. Warm temperatures speed up the metabolism of zooxanthella, causing it to produce a toxic compound. In response, corals expel algae and their sunscreen, leaving them exposed to harmful UV damage. Since these species get most of their coloring from zooxanthellae, the expulsion causes the corals to “whiten” or appear lighter, changing from a dark shade to a paler shade.
Bleaching affects the ability of some corals to reproduce successfully. By expelling their zooxanthellae and therefore losing their UV protection, the DNA of corals is more likely to be damaged. Specifically, changes in the mitochondria of their sperm can affect their motility (ability to swim) in the long term. If they fail to reproduce, corals cannot create new offspring which may have genetic changes that make them more resistant to warming and help them adapt to changes in the oceans.
Following the 2014 and 2015 bleaching events in Hawaii, the team observed that blue rice coral had exceptional reproductive vigor at 90% motility. In contrast, the motility of its brown pigmented counterparts was only half that value. This suggests that even if brown corals survive bleaching and appear visually healthy, damage from bleaching and UV exposure could have lasting impacts on their ability to reproduce successfully. A key factor in the blue rice coral’s ability to reproduce successfully could be its sunscreen pigment, which the coral can retain even as it turns white. By better understanding the role that UV protective pigments play in mitigating the adverse effects of climate change and warming oceans, scientists can understand why some species are better equipped to survive and thrive in a changing environment than other.
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