Abstract
BackgroundCoral reefs face unprecedented declines in diversity and cover, a development largely attributed to climate change-induced bleaching and subsequent disease outbreaks. Coral-associated microbiomes may strongly influence the fitness of their hosts and alter heat tolerance and disease susceptibility of coral colonies. Here, we describe a new coral disease found in Micronesia and present a detailed assessment of infection-driven changes in the coral microbiome.ResultsCombining field monitoring and histological, microscopic and next-generation barcoding assessments, we demonstrate that the outbreak of the disease, named ‘grey-patch disease’, is associated with the establishment of cyanobacterial biofilm overgrowing coral tissue. The disease is characterised by slow progression rates, with coral tissue sometimes growing back over the GPD biofilm. Network analysis of the corals’ microbiome highlighted the clustering of specific microbes which appeared to benefit from the onset of disease, resulting in the formation of ‘infection clusters’ in the microbiomes of apparently healthy corals.ConclusionsOur results appear to be in contrast to the recently proposed Anna-Karenina principle, which states that disturbances (such as disease) trigger chaotic dynamics in microbial communities and increase β-diversity. Here, we show significantly higher community similarity (compositional homogeneity) in the pathobiome of diseased corals, compared to the microbiome associated with apparently healthy tissue. A possible explanation for this pattern is strong competition between the pathogenic community and those associated with the ‘healthy’ coral holobiont, homogenising the composition of the pathobiome. Further, one of our key findings is that multiple agents appear to be involved in degrading the corals’ defences causing the onset of this disease. This supports recent findings indicating a need for a shift from the one-pathogen-one-disease paradigm to exploring the importance of multiple pathogenic players in any given disease.
Highlights
Coral reefs face unprecedented declines in diversity and cover, a development largely attributed to climate change-induced bleaching and subsequent disease outbreaks
Many coral diseases remain insufficiently characterised and little is known about their aetiologies, transmission dynamics and infection risks, under different climate scenarios [8]
Grey-patch disease (GPD) is macroscopically detectable by the presence of varying-sized mats of thin, greycoloured biofilms occurring at multiple locations on the same colony, which do not appear to be limited to a particular location on a colony (Fig. 1a and Additional file 1: Figure S1)
Summary
Coral reefs face unprecedented declines in diversity and cover, a development largely attributed to climate change-induced bleaching and subsequent disease outbreaks. In 2017, reefs (on a global scale) experienced an extended period of heat stress, which led to the third global bleaching event since the start of records in the 1980s [2]. During this pan-tropical episode of coral bleaching, locations known. The potential ecological importance of coral diseases has been emphasised by Maynard et al [7] who argue that the effect of climate change on coral communities by promoting disease outbreaks may be strong or even stronger than its impact via increased bleaching stress. For many diseases, even the identity of causal agents is in question [9], leading to uncertainty about the total number of described diseases [10]
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