Study reveals the secret of corals’ tolerance to climate change: their diet

Researchers from the Faculty of Biological Sciences and the Swire Institute for Marine Sciences, University of Hong Kong, have developed a new method to determine what corals eat, and showed that dependence on certain nutritional sources supports their susceptibility to bleaching in the warming of the oceans.

The research, published in the prestigious magazine. Scientific advances, solves a puzzle scientists have struggled with for decades: determining a coral’s diet involves measuring the amount of prey it captures with stinging tentacles, as well as the amount of food provided by photosynthetic algae within its cells. To overcome this challenge, the team, led by Dr. Inga Conti-Jerpe, compared the stable isotope “fingerprint” of hundreds of corals collected in Hong Kong with that of their associated algae. The results showed that some corals have isotopic fingerprints that match those of their algae, indicating that the two partners share nutrients. Other corals have different fingerprints than their algae due to a diet based on capturing and consuming prey particles in the water. The researchers found that more predatory corals had significantly larger polyps (a single coral unit, much like an anemone) than the more photosynthetic-dependent corals, a controversial relationship previously proposed for the first time in 1974.

“We knew that the size of the polyp is a factor that affects the surface / volume ratio of a coral, a trait that other scientists have observed that could be related to late bleaching in the field. We decided to conduct a warming experiment with our corals. Hong Kong to see if their diet accurately predicted how long they could withstand high temperatures without bleaching, and it did, “explains Dr. Conti-Jerpe.

These results have implications for how coral reefs will change as climate change progresses. Corals that depend on photosynthesis bleach faster, while predatory corals can withstand longer heating temperatures. “The results of our study help predict which coral species are most likely to survive as the oceans heat up. Unfortunately, what we found is that the most susceptible species are those that are commonly used in reef restoration efforts. coral. To ensure long-term success of reef rehabilitation, restoration efforts should focus on bleaching-resistant species, “said Dr. David Baker, associate professor, College of Biological Sciences and Swire Institute of Science. Marinas who supervised the study.

While predatory nutrition may confer protection against bleaching, the scientists point out that, given the sustained elevated temperature, all species in the study were eventually bleached. “Capturing a large amount of food does not prevent corals from fading,” explains Dr. Conti-Jerpe, “it just gives them a little more time, the time they desperately need.” The results of this study will help scientists, conservationists, and policymakers anticipate which corals will disappear first and how this will change reef ecosystems in general, including the services they provide.

Stable isotope data is an established tool for investigating diet: it is derived from the measurement of different forms of common elements, such as carbon and nitrogen, which have the same function biologically but differ slightly in mass. For example, nitrogen, an essential component for DNA and protein, comes in a common ‘light’ (14N) isotope and a rare ‘heavy’ (15N) isotope. When it comes to diet, animals accumulate 15 N if they are sitting higher up the food chain: a carnivore will have more 15 N than a herbivore. The corals in this study that had stable isotope values ​​different from those of their algae had more 15N and therefore must be more predatory.