How to beat bleaching

You’d have thought that the ability to produce your own food was a handy trait in any circumstance – and here we’re not just considering humans in a coronavirus-crippled world.

200414 coral closeup
Close up of a large-polyped coral (Turbinaria sp. ) showing individual polyps. Credit: Dr. Philip D. Thompson

Consider corals. Autotrophic corals have small polyps and produce food through symbiotic relationships with algae. Heterotrophic corals have large polyps and do not produce their own food – they have to capture it.

According to research just published in the journal Science Advances, it turns out that autotrophic corals may be the first to succumb to bleaching caused by rising sea temperatures. Heterotrophic corals may survive longer.

The findings can help scientists better understand which traits give coral species a survival advantage under climate change. They suggest that conservation interventions focused exclusively on restoring autotrophic corals may be misguided.

Although defining a coral species’ trophic niche (what it eats and what it is eaten by) is important for understanding how it will fare as climate change alters its environment, the symbiotic relationships between coral and algae have made this challenging.

To better understand whether the way in which corals attain nutrients affects their resistance to bleaching, Inga Conte-Jerpe, from the University of Hong Kong, and her colleagues analysed carbon and nitrogen isotope data from five stony coral families and their microalgae. The data was gathered from 23 sites across Hong Kong.

The research team also tested heterotrohy as a predictor of bleaching resistance in seven species during a 70-day warming experiment; all coral species analysed hosted the Symbiodiniacea species of algae except one, which hosted a species with similar heat tolerance.

Using standardised colour cards to measure the corals’ decline, the researchers observed that the autotrophs bleached earlier than heterotrophs.

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