Abstract
BackgroundDeclining water quality coupled with the effects of climate change are rapidly increasing coral diseases on reefs worldwide, although links between coral diseases and environmental parameters remain poorly understood. This is the first study to document a correlation between coral disease and water quality on an inshore reef.Methodology/Principal FindingsThe temporal dynamics of the coral disease atramentous necrosis (AN) was investigated over two years within inshore populations of Montipora aequituberculata in the central Great Barrier Reef, in relation to rainfall, salinity, temperature, water column chlorophyll a, suspended solids, sedimentation, dissolved organic carbon, and particulate nitrogen, phosphorus and organic carbon. Overall, mean AN prevalence was 10-fold greater during summer wet seasons than winter dry seasons. A 2.5-fold greater mean disease abundance was detected during the summer of 2009 (44 ± SE 6.7 diseased colonies per 25 m2), when rainfall was 1.6-fold greater than in the summer of 2008. Two water quality parameters explained 67% of the variance in monthly disease prevalence in a Partial Least Squares regression analysis; disease abundance was negatively correlated with salinity (R2 = −0.6) but positively correlated with water column particulate organic carbon concentration (R2 = 0.32). Seasonal temperature patterns were also positively correlated with disease abundance, but explained only a small portion of the variance.Conclusions/SignificanceThe results suggest that rainfall and associated runoff may facilitate seasonal disease outbreaks, potentially by reducing host fitness or by increasing pathogen virulence due to higher availability of nutrients and organic matter. In the future, rainfall and seawater temperatures are likely to increase due to climate change which may lead to decreased health of inshore reefs.
Highlights
Disease has emerged as a significant threat to wildlife populations in recent decades [e.g.1, 2]
While the link between anthropogenic stress and disease susceptibility is currently poorly understood, it is thought that coral disease is facilitated by a decrease in water quality [22]
Evidence of this exists from the Caribbean [22,23,36] and the Philippines [20] and suggests that anthropogenic stressors and coral disease are linked in complex ways [35]
Summary
Disease has emerged as a significant threat to wildlife populations in recent decades [e.g.1, 2]. The current understanding of marine diseases is poor in comparison to knowledge of human, agricultural and terrestrial wildlife diseases [4] It appears that epidemiological theories developed for terrestrial diseases may not translate well to marine ecosystems [4,5]. Declining water quality coupled with the effects of climate change are rapidly increasing coral diseases on reefs worldwide, links between coral diseases and environmental parameters remain poorly understood. This is the first study to document a correlation between coral disease and water quality on an inshore reef
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