Researchers examine changes in coral microbiome under hypoxia

CALIFORNIA: A recent study provided the first characterisation of the coral microbiome under hypoxia or low oxygen levels in the water.

The study was published in the American Society for Microbiology journal Applied and Environmental Microbiology.

The study is a first step towards discovering potentially helpful microorganisms for corals exposed to this environmental stressor.

The study was carried out because there is a growing knowledge of the impact of the microbiome on host health. A healthy human gut microbiome, for example, is important for digestion, immune system response, and even mental health. The coral microbiome, like the human microbiome, benefits its host, the coral animal.

Disease prevention, nutrient uptake, and resilience to environmental stressors such as rising temperatures and acidity are among them.

Despite this, scientists know far less about the role of the microbiome when corals experience hypoxia. The researchers wanted to understand how the microorganisms living on the coral’s surface react to hypoxia. They thought the work may provide insights into how symbiotic microbes respond to host and environmental stress.

The researchers conducted their experiments in Bahia Almirante, Bocas del Toro, Panama. “We picked this site because we have seen hypoxic events here associated with human activity, including agriculture and coastal development,” said lead study author Rachel Howard, PhD candidate, Department of Soil, Water and Ecosystem Sciences, University of Florida.

“We established experimental chambers which lowered dissolved oxygen on patches of coral reef. We then sampled the microorganisms living on corals in those chambers and corals outside the chambers after 2 days to see how the community of microbes differed with and without the stress of low oxygen.”

The researchers found that when oxygen levels dropped, the overall coral microbiome changed after only 48 hours, and the number of some specific types of bacteria increased.

The bacteria that increase are those that can survive without oxygen and are ready to take advantage of a change in resources. When there is not enough oxygen in the water, it throws the community of microorganisms on the coral out of balance, and some of the suspected harmful bacteria, such as Desulfovibrionaceae or Clostridia, become more active.

“Because corals vary in their sensitivity to deoxygenation and given the crucial role of microorganisms in coral health, we suggest that changes in the microbiome may influence coral resilience to low oxygen conditions. Episodes of low oxygen, along with other impacts of climate change, pose a threat to coral and other marine organisms,” Howard said.