University of Derby researchers identify new disease threat to coral reefs

A previously undiscovered disease which threatens the health of coral reefs has been found by researchers from the University of Derby.

Grey Patch Disease (GPD) was found among coral in Micronesia by a team led by Dr Michael Sweet, Associate Professor in Aquatic Biology, and head of the University’s Aquatic Research Facility (ARF).

The disease materialises in the form of a cyanobacterial film with the appearance of a grey patch. It has been found on 18 different species of coral, and varying in size from a few centimetres across to one square metre.

Dr Sweet said: “Given the range of threats to the health of the world’s coral reefs, the emergence of any new disease which can drastically reduce coral cover at local and regional scales could pose a major threat to coral reefs around the world, particularly as our climate continues to change.

“While Grey Patch disease appears to be limited to Micronesia at present and progresses slowly, it is clearly capable of infecting a large array of species. In the case of one species of coral infected, more than one-fifth of its colonies in the Luminao reef, off the island of Guam, were found to have the disease, which shows it can spread to epidemic proportions.”

The findings of the research have now been published in the journal Microbiome.

Dr Sweet said: “We know very little about the 23 or so diseases which affect corals, their causes, signs, transmission and infection risks for example, not to mention how each of these elements could be affected by different climate scenarios.

“However, what we do know from our observation of this disease is that cyanobacteria are quite capable of penetrating previously healthy coral tissue and creating the conditions which lead to the formation of the grey biofilm patches. Further, we show that the causal agent is not a single pathogen. In fact, it’s quite clearly multiple pathogens working together. We identify a number of key bacteria, ciliates and fungi, which all appear to play specific roles in the onset of this disease.”

He added: “There are telltale signs that the disease is progressing when we come across these infected corals in the reef. The presence of small bubbles for example, emerging from the diseased patches tells us that primary production of the microbes making up the biofilm are very much active. But we also observed examples of where the coral can fight back against the disease. In these cases re-sheeting over the lesions occurs and the corals live on to fight another day.”

“Nevertheless, despite some corals being able to recover, this disease poses another significant concern for the health not just of coral, but of entire ecological communities which depend upon the reefs.”

“Our work highlighted some interesting findings, which we hope to explore further. Specifically, our study indicated that apparently healthy corals harboured specific microbes, which were usually more prevalent in diseased tissues than the healthy tissue. We called these clusters of microbes ‘infection clusters’ and they appear to indicate that the ‘healthy’ coral may already be sick. If this holds true, identification of such infection clusters may serve as an early warning system for checking the health state of any given reef.”

The University’s Aquatic Research Facility is also conducting world-leading research in the field of coral spawning and reproduction. Here, Dr Sweet and his team move away from documenting the demise of reefs around the world and attempt to move the field of coral restoration forward with their discoveries and innovative science.

Another member of Dr Sweet's research team, Dr Till Roethig highlighted another angle of the cutting edge research being undertaken at the University by winning a prestigious award from the International Coral Reef Society – in the study to follow, he hopes to investigate how corals respond to changes in salinity, a lesser known stressor associated with climate change.