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Key to corals' bleaching susceptibility lies in their diet shows new study co-authored by ASE/EOS PhD student

21 Apr 2020

Climate change and warming oceans are major threats to coral reefs and can cause widespread coral bleaching. As coral scientists and conservationists work against the clock to restore and preserve coral reefs, new research has revealed some corals have a secret to help them tolerate climate change. A study led by Dr. Inga Conti-Jerpe at the School of Biological Sciences and Swire Institute of Marine Science, The University of Hong Kong, and co-authored by ASE PhD student Ms Molly Moynihan reveals that a key to corals’ susceptibility to bleaching lies in their diet. The study is published in the highly ranked journal Science Advances.

The researchers behind the study suspected diet might be an important factor for how well corals tolerate warming, but this had never been studied before, partly due to the complicated nature of corals’ diets. Corals are animals that can get their energy both from capturing prey with stinging cells called nematocysts and by providing a home to photosynthetic algae, who share nutrients with the coral in return. They can use both strategies simultaneously, and the strategy they rely on most varies with species and environmental conditions. This makes it tricky for scientists to identify the main source of nutrients; a problem the researchers in this study solved by using stable carbon (C) and nitrogen (N) isotopes to track the nutrients in the coral tissue.

The results show that corals which rely more on capturing prey could cope better with warming waters, while those that rely on photosynthetic algae are more vulnerable. This has important implications for conservation and restoration of coral reefs. “The results of our study help predict which coral species are more likely to survive as oceans warm. Unfortunately, what we found is that the most susceptible species are those that are commonly used in coral reef restoration efforts. To ensure the long-term success of reef rehabilitation, restoration initiatives should shift their focus to bleaching-resistant species.” said Dr. David Baker, Associate Professor at the School of Biological Sciences and Swire Institute of Marine Science who supervised the study.

Unfortunately, while predatory nutrition can confer some protection from bleaching, predatory corals are by no means immune to the effects of warming oceans: The scientists note that given sustained elevated temperatures, all the species in the study eventually bleached. “Capturing a lot of food doesn’t save corals from bleaching,” explains Dr. Conti-Jerpe, “it just buys them a little more time – time that they desperately need.” The findings of this study will help scientists, conservationists and policy makers anticipate which corals will disappear first and how this will change reef ecosystems overall, including the services they provide.

Ms. Molly Moynihan is currently a PhD student at the Earth Observatory of Singapore and Asian School of the Environment at NTU Singapore. She became involved in this research during an internship at the University of Hong Kong and has continued to collaborate with Dr. Baker’s group on this project, as well as for her own PhD research, while at NTU.

HKU Press release

Original publication in Science Advances