The term ‘coral disease’ is generally used to refer to the broad range of ailments exhibited by corals when exposed to biological stressors, including bacteria, fungi and viruses, as well as nonbiological stressors, such as increased sea surface temperatures, ultraviolet radiation and pollutants. Coral disease has increased significantly over the last 10 years, causing widespread mortality among reef-building corals, which can have negative impacts to the general health of the surrounding reef ecosystems.
This week however, it has been revealed how marine reserves set up along the Great Barrier Reef have shown to significantly enhance coral health, with researchers finding the reserves reduce the prevalence of various coral diseases. These marine reserves or ‘no-take zones’, were originally established in an effort to prevent the overfishing of the reef and reduce the ecosystem damage associated with fishing activity (such as pollution) and have yielded positive results. The idea that these marine reserves are also having a positive impact on the overall health of corals on the reef had not been previously investigated and proved an unexpected bonus.
Researchers from the ARC Centre of Excellence for Coral Reef Studies at James Cook University found that coral disease levels were four times lower inside no-take marine reserves, where fishing is banned, compared to outside reserves.
“We surveyed more than 80,000 corals around the Whitsunday Islands for six different diseases that commonly harm reef corals around the world,” says study lead author, Dr Joleah Lamb from the Coral CoE.
“We found three coral diseases were more prevalent on reefs outside no-take marine reserves, particularly on reefs with high levels of injured corals and discarded fishing line.”
The team has theorised that the reason for higher disease outbreaks found oustide of no-take zones is that wounded corals are more vulnerable to disease. Damaged tissue cause by discarded fishing equipment and coral breakage attributed to a variety of fishing-related activities provides sites where pathogens and parasites can invade, particularly as coral immune responses are lowered while they heal. Thus, in areas where fishing is prohibited, the physical damage inflicted on corals is reduced and in turn reduces the onset of diseases in corals.
“Fishing line not only causes coral tissue injuries and skeleton damage, but also provides an additional surface for potential pathogens to colonise, increasing their capacity to infect wounds caused by entangled fishing line,” Dr Lamb says.
The researchers hope their findings send a clear message to reef managers about the benefits of marine reserves for coral health.
“No take marine reserves are a promising approach for mitigating coral disease in locations where the concentration or intensity of fishing effort is relatively high,” says Professor Garry Russ from the Coral CoE.
Professor Bette Willis, also from the Coral CoE, says the scientists are now expanding their research to examine other drivers of coral disease.
“We’ve shown that there are strong links between damage and disease in this study, now we’re interested in understanding and managing other potential drivers of diseases that involve injury– such as outbreaks of crown-of-thorns starfish, cyclones, and recreational activities like anchoring.”
The teams findings are particularly significant at this point in time as the risk of coral disease outbreaks on the Great Barrier Reef is likely to increase as the impacts of climate change place reefs under additional stress.
Rising sea surface temperatures may increase the frequency and severity of coral disease outbreaks throughout the Great Barrier Reef Marine Park. Rising sea temperatures can lead to coral bleaching, a response to a stressor exhibited by coral whereby it expels its symbiotic algae. Even if corals recover from bleaching, the weakened corals are often more vulnerable to disease. On the Great Barrier Reef, the Australian Institute of Marine Science recorded a substantial increase in coral disease following the 2002 mass coral bleaching event. An increase in storms and cyclones attributed to climate change can also damage corals over large areas, and increase turbidity, nutrients and algal blooms, all of which can increase the susceptibility of corals to disease.
From the teams findings, they conclude that disease mitigation through reductions in physical injury in areas where human activities are concentrated could be a successful mechanism by which protected areas may improve ecosystem resilience in a changing climate.
Photo Header Credit:
Green Peace A Greenpeace activist holds a banner under a fish aggregation device (FAD) calling for “Marine Reserves Now”. Greenpeace is calling for the establishment of a global network of marine reserves.
- Joleah B. Lamb, David H. Williamson, Garry R. Russ, Bette L. Willis.Protected areas mitigate diseases of reef-building corals by reducing damage from fishing. Ecology, 2015; 150422141041004 DOI:10.1890/14-1952.1