Spatial extent of dysbiosis in the branching coral Pocillopora damicornis during an acute disease outbreak

Abstract

Abstract Globally, coral reefs are experiencing increased disease prevalence and the continuing emergence of large-scale outbreak events. Acute coral disease outbreaks are an immediate threat to coral reefs, but also provide an opportunity to identify the underlying microbial and functional patterns indicative of coral disease, and whether these can serve as indicators of disease risk. Outbreak events also allow testing of prevailing theory on how reef-building corals respond to disease, either systemically as whsole individuals or as heterogeneous colonial organisms. Here, we coupled assessment of coral meta-organism structure (microbiome) and function (metabolome) in Pocillopora damicornis during an outbreak of tissue loss disease to determine whether dysbiosis indicated disease in tissues without visual signs of impact. Coral fragments with visual evidence of disease are characterized by higher variance in microbial community structure and metabolic function, indicating disruption of the meta-organism. However, these indicators are absent in the microbiome and metabolome of visibly-healthy fragments sourced from the same diseased colonies. A lack of systemic, colony-wide disease response challenges the notion that broad dysbiosis could serve as a pre-visual indicator of disease and invites renewed discussion of how we assess the health of colonial corals.