Corals in Palau's Nikko Bay spared from mass bleaching, new study confirms


Nikko Bay’s corals have shown little evidence of bleaching during the 1998 mass bleaching on other reefs of Palau and during the 2010 thermal stress event. Photo courtesy of PIRCRC

While ocean warming and acidification are considered major threats to coral reefs on a global scale, new research in Palau found that corals in Ngermid Bay have the potential to adapt to high temperatures.


Ngermid Bay’s corals have shown little evidence of bleaching during the 1998 mass bleaching on other reefs of Palau and during the 2010 thermal stress event, according to research by Palau International Coral Reef Center (PICRC) and the University of the Ryukyus recently published in the Scientific Reports.


A global mass bleaching event that occurred in 2016 and 2017 affected only the eastern parts of Micronesia.


The authors noted that Palau’s sea surface temperature rapidly shifted in March 2016 and reached above 30 °C in June 2016 but quickly decreased afterward. They noted that bleached corals quickly recovered, hence the size of live coral cover to remain the same.


The research team studied Ngermid Bay-- also known as Nikko -- in the inner reef area with high carbon dioxide and high-temperature conditions, and counter-intuitively, high coral coverage.


"Examining calcification, photosynthesis and respiration rates of corals in the bay and outside the bay, the authors of the study suggest that corals have the potential to acclimate and adapt to those warm and acidic conditions," PIRCRC said.


Researchers found that the seawater environment in the semi-closed bay was warmer (1-2 ℃ higher) and more acidic (0.3-0.4 lower pH) compared to outside of the bay.


"These environmental conditions are similar to what is expected to occur in the ocean by the end of this century due to climate change, and these conditions are expected to be detrimental for most coral species," PIRCRC said.


"However, highly diverse and healthy coral communities were found within the bay."


The study was led by Dr. Haruko Kurihara from the University of the Ryukyus and include other researchers from University of the Ryukyus, PICRC, Tokyo Institute of Technology, The Sasakawa Peace Foundation, and Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology.


The research cited some studies indicating that zooxanthellate corals may have the ability to adapt to high-temperature environments, such as by shuffling to Symbiodiniaceae types that have higher tolerances to warmer temperatures.


The authors have observed that the tolerance of organisms to high carbon dioxide can differ among species and even within species.


"Hence, there is now widespread interest in understanding how reef organisms will respond to ocean warming and acidification at the community level, and to examine if organisms are able to acclimatize or adapt to these environmental changes," they said.


PIRCRC said evaluating the mechanisms underlying the processes will help scientists understand how organisms have adapted and evolved under the changing environment that occurred in the past.


"Additionally, those data may give hints for potential conservation strategies for corals under future climate change," PIRCRC said.


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Ocean acidification is a reduction in the pH of the ocean over time, caused primarily by the uptake of carbon dioxide from the earth’s atmosphere.


Ocean acidification reduces the amount of calcium carbonate available, which marine organisms need to build their shells or skeletons.


Marine organisms such as corals, clams, crabs and other shellfish may be threatened as OA continues to increase due to high concentrations of CO2.


"Therefore, our livelihood, economy, and culture will eventually be affected by OA as we are dependent on our ocean and marine life," PIRCRC said.




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