Genetic model predicts massive coral mortality

(ORDO NEWS) — The sensitivity of individual corals to high temperatures is determined by hereditary factors. The researchers came to this conclusion after analyzing 237 samples of Acropora millepora coral from the Great Barrier Reef. In this case, the decisive role is played not by any specific genes, but by their totality.

The findings provided the basis for a model that will predict the vulnerability of individual coral reefs and help develop conservation measures. However, even the use of genetics will only buy time to combat the main threat to corals – climate change. The research results are published in the journal Science.

Corals are extremely sensitive to ambient temperatures. When the water gets too warm, they lose the symbiotic dinoflagellate algae and discolor. If conditions remain unfavorable for too long, corals die.

In recent decades, against the backdrop of climate change, massive bleaching of coral reefs is occurring with increasing frequency: for example, the Great Barrier Reef has experienced three such episodes in the last five years alone. If the planet continues to heat up, coral reefs around the world are at risk of extinction this century.

However, not all coral species are equally vulnerable to bleaching. Moreover, even among representatives of the same species, sensitivity to high temperatures differs. A team of researchers led by Zachary L. Fuller from Columbia University decided to find out what the genetic basis of this variation is.

Experts conducted a genome-wide analysis of 237 samples of Acropora millepora coral taken from 12 sites on the Great Barrier Reef at the peak of bleaching in 2017. The genetic data was compared with the degree of damage suffered by individual colonies.

It turned out that tolerance to high temperatures is provided not by individual genes, but by combinations of many genes, each of which has a relatively small effect. Based on the polygenic assessment, as well as data on the genome of symbiotic algae and environmental features, the authors were able to create a model that predicts the vulnerability of individual evolutionary lines of A. millepora to climatic changes. It can be used to identify the most vulnerable reefs or to sample corals for culture.

The researchers believe a similar approach could be used to create models that predict the risk of bleaching in other coral species. However, genetics alone is not capable of saving coral reefs from extinction, the authors emphasize. To give these rich ecosystems a chance to survive, greenhouse gas emissions must be reduced as soon as possible.

Some corals do not turn pale in response to high temperatures, but take on an unusually bright color. Researchers have established that it serves as a kind of analogue of sunscreen. The proteins that provide the acid coloration protect the coral from ultraviolet radiation, which increases the chances of symbionts returning.

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