Seasonal rainfall and runoff promote coral disease on an inshore reef

Background

Declining water quality coupled with the effects of climate change arerapidly increasing coral diseases on reefs worldwide, although links betweencoral diseases and environmental parameters remain poorly understood. Thisis the first study to document a correlation between coral disease and waterquality on an inshore reef.

Methodology/Principal Findings

The temporal dynamics of the coral disease atramentous necrosis (AN) wasinvestigated over two years within inshore populations of Montiporaaequituberculata in the central Great Barrier Reef, in relationto rainfall, salinity, temperature, water column chlorophylla, suspended solids, sedimentation, dissolved organiccarbon, and particulate nitrogen, phosphorus and organic carbon. Overall,mean AN prevalence was 10-fold greater during summer wet seasons than winterdry seasons. A 2.5-fold greater mean disease abundance was detected duringthe summer of 2009 (44 ± SE 6.7 diseased colonies per 25m²), when rainfall was 1.6-fold greater than in the summer of2008. Two water quality parameters explained 67% of the variance inmonthly disease prevalence in a Partial Least Squares regression analysis;disease abundance was negatively correlated with salinity(R2 = −0.6) but positively correlated with watercolumn particulate organic carbon concentration(R2 = 0.32). Seasonal temperature patterns were alsopositively correlated with disease abundance, but explained only a smallportion of the variance.

Conclusions/Significance

The results suggest that rainfall and associated runoff may facilitateseasonal disease outbreaks, potentially by reducing host fitness or byincreasing pathogen virulence due to higher availability of nutrients andorganic matter. In the future, rainfall and seawater temperatures are likelyto increase due to climate change which may lead to decreased health ofinshore reefs.