Koch at the reef — Understanding coral disease

Corals are host to a mixture of microbes — prokaryotes, protists, and viruses — that play critical functional roles within their host. During unfavourable environmental conditions, coral immunity becomes compromised, fostering the proliferation of alien pathogens or previously resident microbes that turn pathogenic. Coral disease can persist over months or years, pushing the coral into a chronically stressed state. In severe cases, epizootics such as Stony Coral Tissue Loss Disease (SCTLD) can spread through entire reefscapes, turning vibrant communities from reefs to rubble.

Here we explore several coral diseases — black band disease, red band disease, Caribbean ciliate infection, SCTLD, and dark spots disease — teasing apart pathobiome structure, dynamics, and expression during pathogenesis across multiple scleractinian hosts: Pseudodiploria strigosa, Orbicella faveolata, Diploria labyrinthiformis, Dendrogyra cylindrus, and Stephanocoenia intercepta. Sampling was conducted in Curaçao off the leeward coast at multiple sites during October 2022 and March 2023. Triplicate coral samples were taken from healthy tissues, apparently healthy tissue from diseased hosts, the disease transition zone, and dead skeleton. Coral 16S/18S rRNA genes were sequenced from ~250 samples, allowing exploration of both prokaryotic and microeukaryotic community dynamics across diseases. Additionally, RNA sequencing was conducted using poly-A selection/enrichment to observe the host transcriptional response through disease progression.

We aim to characterise the prokaryotic and eukaryotic taxa recovered from several diseases to disentangle microbial variability between visually healthy and diseased individuals, and to identify the host response and likely immunological functions at the cellular level through disease progression.