A new disease, likely fuelled by climate change, killing coral reefs in Western Pacific Ocean

Experts say the grey-patch disease strikes by altering the corals' defenses and will influence the health of future reefs.


                            A new disease, likely fuelled by climate change,  killing coral reefs in Western Pacific Ocean

Climate change is believed to have introduced a new disease among corals in the Western Pacific Ocean, finds a new study. Called the grey-patch disease, it strikes by altering the coral's defenses.

"This disease, along with another disease called Porites white patch syndrome, are going to be major players in the health of future reefs as these ancient colonies fall foul to the two diseases and leave little but rubble in their wake", warns Dr. Michael Sweet, Associate Professor at the University of Derby and the lead author of a study on the topic. 

Characterised by the growth of a thin grey layer on its surface, the disease appears to be caused by multiple pathogens. (Michael Sweet)

Corals are defended by a distinct community of microbes, which has shown to strongly influence coral survival. A weak defense system means corals become more vulnerable to attack from other pathogens - similar to how humans catch a cold, for instance, says Dr. Sweet. 

Coral diseases can be attributed to climate change as the reef communities are sensitive to the environmental effects of warming waters. "Increases in sea surface temperature may be weakening the corals' immune defense, allowing pathogens to take hold", Dr. Sweet told MEA WorldWide (MEAWW). 

Warmer water temperatures make corals let go of the algae living in their tissues, causing them to turn white - called coral bleaching. Corals can survive a bleaching event, but it leaves them vulnerable to diseases, stunts their growth, affects their reproduction, and impacts other species that depend on the coral communities. Due to an increase in bleaching events and subsequent infection by disease, coral reefs are declining, says the study.

The disease, which was seen in 21.7% of surveyed colonies, currently affects 18 different species of coral. Characterized by the growth of a thin grey layer on its surface, the disease appears to be caused by multiple pathogens, says the team. "It really is a disease caused by a number of pathogens from different kingdoms - fungi, ciliates, and bacteria - all playing their specific role in the demise of the giant coral colonies", Dr. Sweet told MEAWW. "

Dr. Sweet and colleagues surveyed the Indian and Pacific Oceans for signs of this new disease between 2011 and 2018. Their search revealed that disease is currently restricted to Micronesia, a part of Oceania in the western Pacific Ocean. Although the disease was able to infect multiple species, the authors found it was slow to progress.

One of the prime victims of this particular disease was Porites, which are regarded as the stronger members of the coral community as it often resists other climate-induced threats like bleaching for example, says Dr. Sweet.

The authors also found that the microbiome of each coral was significantly altered after infection. However, when comparing microbiomes across different corals, those with the disease had a similar profile of microbes, which is consistent with previous research. 

Sweet and his colleagues believe that the corals can be saved. "There are the good bacteria, clinging on to life and trying to help the coral fight the disease. For grey patch disease, it appears these good bacteria may actually win every now and again and the disease regresses, with tissue regrowing over the denuded or exposed coral skeleton," Dr. Sweet said. "We are now interested in exploring if these microbes may be cultured and used as probiotics to assist corals in overcoming the impacts of climate change", he adds.    

The findings are published in Microbiome.

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