Koch at the reef - Understanding coral disease

Corals are host to a mixture of microbes containing prokaryotes, protists, and viruses that play critical functional roles within their host. During unfavourable environmental conditions the coral immunity gets compromised, fostering proliferation of alien pathogens, or previously residential microbes that become malicious. Corals are considered relatively resilient with respect to short-term stress events, with a molecular toolkit that provide mechanisms to mitigate physicochemical changes. Coral disease can persist over months/years, pushing the coral into a stressed state for long-periods of time. Stress events ultimately breakdown homeostasis, disrupting the normal processes involved in routine maintenance, shuttling resources to build immune-related proteins and enzymes. Corals are susceptible to a wide variety of maladies that have critical impacts on host physiology, fecundity, and survivorship. In severe cases, epizootics such as Stony Coral Tissue Loss Disease (SCTLD) outbreak can spread through entire reefscapes turning vibrant complex communities from reefs to rubble. Many other coral diseases have persisted on reefs through time, having chronic effects on coral reef succession.

Here we explore several coral diseases (black band disease, red band disease, Caribbean ciliate infection, stony coral tissue loss disease, and dark spots disease), teasing apart pathobiome structure, dynamics, and expression during pathogenesis across multiple scleractinian hosts, Pseudodiploria strigosa, Orbicella faveolata, Diploria labyrinthiformes, Dendrogyra cylindrus, and Stephanocoenia intercepta. Sampling was conducted in Curaçao off the leeward coast ranging from Playa Kalki (12.380 N 69.160 W), Playa Lagun (12.320 N 69.152 W), CARMABI (12.121 N 68.970 W), Water Factory (12.110 N 68.953 W), Double Reef (12.110 N 68.950 W), and Jan Thiel (12.075 N 68.881 W) during October 2022 and March 2023. Triplicate coral samples were taken from the following areas of interest: healthy tissues (healthy hosts), apparently healthy (healthy tissue from diseased host), disease transition line, and dead skeleton (post-infection). 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 analyze and characterize the prokaryotic and eukaryotic taxa recovered from several diseases to disentangle microbial variability between visually healthy and diseased individuals through a robust sampling design. Additionally, we aim to identify the host response to several coral diseases and characterize the likely immunological functions happening at the cellular level in various locations on the coral through disease progression. We hypothesize that despite immune functions being standard response to stress, the coral host will respond differently to each disease based on the known disease pathogenesis.