Ocean warming and acidification have complex interactive effects on the dynamics of a marine fungal disease

Abstract

Diseases threaten the structure and function of marine ecosystems and are contributing to the global decline of coral reefs. We currently lack an understanding of how climate change stressors, such as ocean acidification (OA) and warming, may simultaneously affect coral reef disease dynamics, particularly diseases threatening key reef-building organisms, for example crustose coralline algae (CCA). Here, we use coralline fungal disease (CFD), a previously described CCA disease from the Pacific, to examine these simultaneous effects using both field observations and experimental manipulations. We identify the associated fungus as belonging to the subphylum Ustilaginomycetes and show linear lesion expansion rates on individual hosts can reach 6.5 mm per day. Further, we demonstrate for the first time, to our knowledge, that ocean-warming events could increase the frequency of CFD outbreaks on coral reefs, but that OA-induced lowering of pH may ameliorate outbreaks by slowing lesion expansion rates on individual hosts. Lowered pH may still reduce overall host survivorship, however, by reducing calcification and facilitating fungal bio-erosion. Such complex, interactive effects between simultaneous extrinsic environmental stressors on disease dynamics are important to consider if we are to accurately predict the response of coral reef communities to future climate change.

Disease dynamics of Porites bleaching with tissue loss: prevalence, virulence, transmission, and environmental drivers

“…Coral disease prevalence can be expected to show intricate interactions with a variety of driving factors (Williams et al 2010(Williams et al , 2014. For example, an increase in temperature can lead to an increase in pathogen virulence or cause stress to the host, which can increase its susceptibility to disease (Harvell et al 2002).…”

“…We have just begun to understand the complex web of interactions between environmental factors and disease prevalence exemplified by studies that applied a multi-factor approach to studying coral disease dynamics (e.g. Bruno et al 2007, Haapkylä et al 2007, McClanahan et al 2009, Williams et al 2010, 2014, Aeby et al 2011a.…”

“…In fact, the geographical extent, number of species affected, and incidence of new diseases are increasing globally (Harvell et al 1999, Ward & Lafferty 2004, Sokolow 2009). Environmental stress, shifts in virulence of existing pathogens, introduction of novel pathogens from anthropogenic activities, and global climate change are associated with this increase (Harvell et al 1999, Sokolow 2009.Coral disease prevalence can be expected to show intricate interactions with a variety of driving factors (Williams et al 2010(Williams et al , 2014. For example, an increase in temperature can lead to an increase in pathogen virulence or cause stress to the host, which can increase its susceptibility to disease (Harvell et al 2002).…”

“…We have just begun to understand the complex web of interactions between environmental factors and disease prevalence exemplified by studies that applied a multi-factor approach to studying coral disease dynamics (e.g. Bruno et al 2007, Haapkylä et al 2007, McClanahan et al 2009, Williams et al 2010, 2014, Aeby et al 2011a.Additionally, different coral diseases can show varying levels of ecological impact. For example, black band disease (BBD) and white syndromes often cause severe colony mortality (Edmunds 1991, Bruckner et al 1997, Roff et al 2006, Aeby et al 2010, Williams et al 2011a), whereas corals with Porites ulcerative white spot syndrome (PUWS) in the Philippines often show complete recovery after infection (Kaczmarsky 2006).…”

The roles of endolithic fungi in bioerosion and disease in marine ecosystems. II. Potential facultatively parasitic anamorphic ascomycetes can cause disease in corals and molluscs

“…Fungi responsible for coral lesions have been found to grow slower under reduced pH, which could slow down the temperature-induced progression of fungal diseases of corals (Williams et al 2014). However, the authors suggest that the effect for bioeroding fungi would be similar as stated above: The effects of acidification on the skeletal properties of the host organism may favour faster degradation of the skeleton.…”