Researchers have developed a new method for determining what corals eat, and have demonstrated that reliance on certain nutritional sources underpins their bleaching susceptibility in heating oceans.
The team, based out of the School of Biological Sciences and Swire Institute of Marine Science at The University of Hong Kong, compared the stable isotope ‘fingerprint’ of hundreds of corals collected in Hong Kong to that of their associated algae. They measured how much prey it captures with stinging tentacles as well as how much food is provided by the photosynthetic algae inside their cells.
“We knew that polyp size is a factor that affects the surface area to volume ratio of a coral, a trait that other scientists have observed might be linked to delayed bleaching in the field,”explains Dr Inga Conti-Jerpe, who led the team. “We decided to run a warming experiment with our Hong Kong corals to see if their diet accurately predicted how long they could withstand elevated temperatures without bleaching – and it did.”
They discovered that some corals have isotopic fingerprints that match that of their algae, indicating that the two partners share nutrients. Other corals have fingerprints that differ from those of their algae due to a diet based on the capture and consumption of prey particles in the water. The researchers found that more predatory corals had significantly larger polyps than those corals more dependent on photosynthesis.
Their findings have significant implications for how coral reefs will change as climate change progresses. Corals that depend on photosynthesis bleach faster while predatory corals can withstand increasing temperatures for longer. The hope is that these findings will help scientists, conservationists and policy makers anticipate how coral reef ecosystems will change as a result of global heating.
“The results of our study help predict which coral species are more likely to survive as oceans warm,” said Dr David Baker, Associate Professor of School of Biological Sciences and Swire Institute of Marine Science who supervised the study. “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.”
While predatory corals were protected to an extent from bleaching, the scientists state that all the species in the study eventually bleached in sustained elevated temperatures.
“Capturing a lot of food doesn’t save corals from bleaching,” added Dr Conti-Jerpe. “It just buys them a little more time – time that they desperately need.”
To read the full paper, “Trophic strategy and bleaching resistance in reef-building corals”, click here.
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