image: This is bleached Acropora coral on the Great Barrier Reef.
Coral reefs support a quarter of all marine life, feed hundreds of millions of people and contribute vastly to the global economy. But they are dying in mass bleaching events, as climate change warms our oceans and breaks down vital relationships between corals and energy-providing algae.
A new commentary, published in Communications Biology from Nature Research, provides hope that a shift in research focus towards coral immunity will support reef conservation and restoration efforts.
Dr Caroline Palmer, Visiting Research Fellow at the University of Plymouth, has spent more than a decade examining coral health from an immunological perspective.
In particular, she has identified coral immune mechanisms and sought to understand what enables some corals to survive while others die. This led Dr Palmer to discover that corals with higher immune defences are less likely to become diseased or to bleach.
In her latest work, she expands on this observation, drawing on a theory from insects that explains how corals might coexist with specific microorganisms, as a 'holobiont', while resisting infection or other disturbances.
Dr Palmer also presents a model of coral susceptibility, whereby investing in immunity enables coral, with its microorganisms, to tolerate more damage before initiating an immune response. This model describes how coral tolerance may vary among corals indicating their susceptibility to disturbances, such as bleaching events.
"There is no question that climate change is devastating coral reef systems. But if we are to conserve or restore them, we need to understand coral health - what drives tolerance and how can we promote it," Dr Palmer says. "If you have a strong immune system, and the energy to support it, you are more likely to be healthy and to survive adverse conditions."
Dr Palmer first started examining the immune systems of reef-building corals more than a decade ago, and her PhD was the first research to look at the subject in depth. But she says that coral immunity remains an under-studied area of research.
Coral bleaching, on the other hand, has been a research focus for decades, though is often considered distinct from immunity - Dr Palmer, however, suggests it is a component of coral holobiont immunity.
Dr Palmer also proposes an immunological model by which corals may increase their tolerance to adverse conditions - suggesting a way coral may adapt to new, more extreme, conditions.
Dr Palmer, who is currently Lead Scientist on the Seeking Survivors project examining coral health in Costa Rica, added: "Coral biologists are racing to conserve coral reefs before it's too late. There is currently a lot of interest in creating more tolerant corals through genetic engineering and of restoring reefs by targeting more resilient corals. I fully support these approaches, but believe understanding what drives coral health will be key to their success."