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A ciliate belonging to theDiadema antillarumscuticociliatosis (DaSc)-associatedPhilasterclade (DaScPc) caused catastrophic long-spined urchin mass mortality in spring and summer of 2022. The ciliate can be grown in culture in both the presence and absence ofD. antillarumtissues, suggesting that it may persist outside its host by consuming microorganisms or dissolved organic nutrients. We hypothesized that DaScPc was present outside its host during and after mass mortality and absent prior to 2022. We examined DaScPc in DNA extracted from 500 swabs of sympatric metazoa and abiotic surfaces, and plankton samples, collected at 35 sites in the Caribbean in 2022 and 2023. DaScPc was detected on corals, turf algae, and a sponge, predominantly at sites with active or prior DaSc. We examined whether it was present prior to 2022 by surveying extracted DNA from Caribbean corals and water collected near corals by PCR and by mining publicly available transcriptomes and metagenomes for DaScPc rRNAs. These efforts yielded no DaScPc genes. We further hypothesized that DaScPc may recruit to the specific corals detected in field surveys, and that these may then infect naïve hosts. A mesocosm experiment to test DaScPc recruitment suggested that, while it recruited to corals, it did so inconsistently between coral species. Incubation of corals that recruited DaScPc with naïve urchins yielded inconclusive results since urchins died without characteristic DaSc signs. Overall, our results suggest that DaScPc may occur outside its urchin host, and that it may have been absent in the region prior to 2022. 

Many marine habitats are at risk due to increasing frequency, intensity, and persistence of harmful algal blooms. Repeated cyanobacterial harmful algal blooms (cyanoHABs) in Florida Bay, USA, kill sponges, resulting in reduced filtration and loss of shelter for benthic species. The loss of these key ecosystem functions can impact disease dynamics if fewer pathogens are filtered from the water column (dilution), if shelter loss increases host density in remaining shelters and a directly transmitted disease is present (host regulation), or if shelter loss changes species distributions and foraging patterns (trophic exposure). We show persistent impacts to hard-bottom communities relative to non-impacted communities 2 yr after a significant cyanoHAB. We compared benthic structure, invertebrate epibenthic/infaunal community composition, and parasitism among macroinvertebrates, stone crab Menippe mercenaria , and Caribbean spiny lobster Panulirus argus . On sites degraded by cyanoHABs, we found more, smaller sponges, indicating regrowth. Despite this evidence of recovery, epibenthic/infaunal invertebrate communities were distinct and more diverse on unimpacted sites. Additionally, there were fewer, smaller bivalves on impacted sites. The bivalve Tucetona pectinata , prey for stone crabs, was nearly absent on impacted sites, resulting in decreased prevalence of the apicomplexan gregarine Nematopsis sp., which is trophically transmitted from T. pectinata to M. mercenaria . Panulirus argus virus 1 also appears to be affected by cyanoHABs, as it was absent on impacted sites but present in 26.5% of spiny lobster on unimpacted sites. Impacts remain evident 2 yr after significant cyanoHABs, which does not bode well for these areas considering the frequent reoccurrence of blooms.