3.6 Current condition and trends of outbreaks of disease, introduced species and pest species
3.6.1 Outbreaks of disease
Whether natural or introduced, disease outbreaks are an indicator of stress in an ecosystem, species or habitat224. They have affected a range of the Region’s species in recent years, including corals92, green turtles225,226, dugongs226 and the Queensland groper227. Coral disease has been identified as a key indicator of coral reef resilience due to its prevalence in disturbed areas228 such as those exposed to flood events116, higher levels of turbidity and sedimentation229, and high sea temperatures230,231. In other countries, degraded coral reef ecosystems are likely to have a high incidence of diseases.232 Coral disease is being increasingly observed on the Great Barrier Reef and is predicted to increase in the future.233,234 Major outbreaks of the naturally occurring white syndrome disease have been recorded after especially warm years on reefs with high coral cover, indicating a potential link between coral disease and increasing sea temperatures as a result of climate change.230,233,235,236 More recently, coral disease has also been linked to cooler-than-normal conditions.230 Reduced salinity can play a role in coral disease. For example, between January and March 2009, following a period of moderately high sea surface temperature and a severe decline in salinity (to 20 parts per thousand), there was a 10-fold increase in the average number of coral colonies infected with disease in Geoffrey Bay, Magnetic Island.231 When salinity returned to normal (about 35 parts per thousand), the average number of diseased colonies declined rapidly.231 Investigations into a suspected outbreak of disease in fishes in Gladstone Harbour concluded that the majority of lesions in barramundi were the result of physical damage after being washed over the Awoonga Dam during heavy rainfall. The stress of their forced relocation and increased crowding and competition for food resulted in the fish becoming more susceptible to parasites and disease.237
White syndrome disease on coral
Disease has affected corals, green turtles, dugong and the Queensland groper in recent years.
Outbreaks of disease have also been observed in species of conservation concern. Green turtle fibropapillomatosis was first reported in Australia more than 40 years ago238 and the frequency of recorded cases increased up to the early 1990s239. In the Queensland population, fibropapillomas are rare on green turtles from offshore reefal environments, but prevalent in semi-enclosed bays.170 There is evidence from other parts of the world of a link to land-based run-off.240 The overall effect on the Region’s population from this disease currently appears to be low241, and there are instances of the species recovering naturally170,242. Necropsies conducted on deceased dugongs indicate disease was the cause of death for between 20 and 25 per cent of the 298 animals examined between 1996 and 2010 for which the cause of death was determined.243 In 2011, after extreme weather, 30 dugongs were recorded as dying of disease or ill health in Queensland.226 Of these, 12 died after extended ill health and had poor body condition, pneumonia was associated with the deaths of three dugongs, and a further 15 died of unidentified disease.
Fibropapilloma lesions around the tail of a young green turtle
© James Cook University, photograph by Ellen Ariel
Disease may be a factor in causing inshore dolphins to strand, as was the case in 2000 and 2001244, but there has been little recent disease monitoring of dolphins within the Region. Investigations into the deaths of 94 Queensland gropers between 2007 and 2011 confirmed that 12 had died from Streptococcus agalactiae infection.227 There is limited information about disease in species that are not iconic or targeted during fishing activities.