Thermal Stress and Coral Cover as Drivers of Coral Disease Outbreaks

Abstract

Very little is known about how environmental changes such as increasing temperature affect disease dynamics in the ocean, especially at large spatial scales. We asked whether the frequency of warm temperature anomalies is positively related to the frequency of coral disease across 1,500 km of Australia's Great Barrier Reef. We used a new high-resolution satellite dataset of ocean temperature and 6 y of coral disease and coral cover data from annual surveys of 48 reefs to answer this question. We found a highly significant relationship between the frequencies of warm temperature anomalies and of white syndrome, an emergent disease, or potentially, a group of diseases, of Pacific reef-building corals. The effect of temperature was highly dependent on coral cover because white syndrome outbreaks followed warm years, but only on high (>50%) cover reefs, suggesting an important role of host density as a threshold for outbreaks. Our results indicate that the frequency of temperature anomalies, which is predicted to increase in most tropical oceans, can increase the susceptibility of corals to disease, leading to outbreaks where corals are abundant.

Temperature induced disease in the starfish Astropecten jonstoni

“…From these various investigations we know that temperature anomalies on tropical coral reefs routinely exceed coral stress thresholds, with temperature considered to be a critical variable in coral hostpathogen systems. For example one large scale investigation along the Great Barrier Reef showed a highly significant relationship between periods of increased water temperature and an emergent disease in Pacific reef-building corals (Bruno et al, 2007). Furthermore increasing water temperatures in reef environments allow pathogens to expand their ecological thermal disease in starfishniche, for example by colonizing low pH environments (Remily & Richardson, 2006).…”

Investigating the Driving Mechanisms Behind Differences in Bleaching and Disease Susceptibility Between Two Scleractinian Corals, Pseudodiploria Strigosa and Diploria Labyrinthiformis

“…A thinning of the SML in response to increasing sea surface temperatures may pose a real threat to the health of all corals since elevated temperature has been shown to be directly associated with increases in both coral bleaching and disease Miller et al 2006;Bruno et al 2007;Muller et al 2008;. Based on the results of this study, the association between increased temperature and bleaching/disease prevalence may be due in part to the thinning of the protective SML barrier.…”

“…Rising temperatures have been associated with an increase in coral bleaching, with bleached corals being more susceptible to disease (Miller et al 2006;Bruno et al 2007;Muller et al 2008;Mydlarz et al 2009; labyrinthiformis showed no sign of disease (Calnan et al 2008). This trend has been observed throughout the wider Caribbean (Edmunds 1991), Belize, and Bermuda (Rützler and Santavy 1983).…”

“…With the onset of global climate change, concern continues to rise for the preservation of coral reefs . It is known that anthropogenic impacts, such as a small 1-2ºC increase in sea surface temperature, can cause bleaching of corals (Mydlarz et al 2009) and that bleaching increases susceptibility to disease (Bruno et al 2007). …”

“…If coral reefs are to be protected and preserved for coming generations, mechanisms of coral resilience to such stressors must be understood . Resilience and resistance to disease and bleaching are particularly important, as both conditions often lead to coral death (Harvell et al 2001;Miller et al 2006;Bruno et al 2007). Corals exhibit a high variability in their resistance to bleaching and disease, both between different species and among colonies of the same species (Raymundo et al 2003;Kaczmarsky et al 2005;.…”