Coral reefs worldwide have been negatively impacted by global warming, but new research suggests that a certain species of microbe may protect them from the changing climate.

Todd LaJeunesse and colleagues from Penn State have reported that an invasive species of unicellular algae that thrives within the cells of coral animals has spread across the Caribbean Sea — and it improves the resilience of coral communities to heat stress associated with the warming climate.

Unfortunately, whereas Symbiodinium trenchii helps improve the coral resilience to heat stress, the micro-algae also diminishes the ability of coral to build reefs, posing a dilemma.

"The results raise a potentially contentious issue about whether this invasion is relatively good or bad for the long-term productivity of reef corals in the Atlantic Ocean and the ecosystems they support," LaJeunesse said.

LaJeunesse and his colleagues employed DNA-sequencing techniques to document the spread of the S. trenchii, which is based in the Indo-Pacific. Their analyses demonstrate that the algae was only recently introduced to the Caribbean and within a short period of time, it has already managed to do some harm.

The research, which was published in the June 1 issue of the Proceedings of the National Academy of Sciences, showed that the algae flourishes within the coral colonies during times marked by a rise in sea-surface temperatures.

During the warming period, the non-native S. trenchii takes the place of the more sensitive native algae species, which their hosts expel when the environment becomes too warm. S. trenchii, however, eventually gets replaced by the native species again after the conditions of the environment return to normal.

Although the invasive algae helps the coral withstand heat during the warming periods, the researchers have found that S. trenchii cuts the calcification rate of corals – the process through which coral reefs are built – in half. This has been notably observed in the Mountainous Star corals.

"This research documents the spread of an opportunistic coral endosymbiont, Symbiodinium trenchii, from the Indo-Pacific into the Greater Caribbean, a region afflicted by human-related impacts including climate warming and environmental degradation," the researchers wrote in their study.

"As a symbiont, it increases the resilience of photosynthetic corals to environmental perturbation but may diminish the animal's capacity to calcify and build reefs."

LaJeunesse said that the results of their research show that S. trenchii may not translocate as many nutrients as the native species to the coral host — which could explain the reduced calcification rates of corals. 

Photo: USFWS - Pacific Region | Flickr

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