Geology topics

Alwin Hylkema

Publications and source records attributed to Alwin Hylkema.

3 recordsLinked to original sources

USGS2025

Investigating the influence of Diadematidae scuticociliatosis on host microbiome composition

Mass mortality of Diadematidae urchins, caused by the Diadema antillarum scuticociliatosis Philaster clade (DScPc) , affected the Caribbean in spring 2022 and subsequently spread to the eastern Mediterranean, Red Sea, and western Indian Ocean. A key question around Diadematidae scuticociliatosis (DSc), the disease caused by the scuticociliate, is whether the urchin microbiome varies between scuticociliatosis-affected and grossly normal urchins. Tissue samples from both grossly normal and abnormal Diadema antillarum were collected in the field during the initial assessment of the DSc causative agent and from an experimental challenge of DScPc culture on aquacultured D. antillarum . Specimens were analyzed using 16S rRNA gene amplicon sequencing. Additional abnormal urchin samples were collected from the most recent outbreak site in the western Indian Ocean (Réunion Island). At reference (i.e., unaffected by DSc) sites, Kistimonas spp. , Propionigenium spp., and Endozoicomonas spp. were highly represented in amplicon libraries. DSc-affected urchin amplicon libraries had lower taxonomic richness and a greater representation of taxa related to Fangia hongkongensis and Psychrobium spp. Amplicon libraries of urchins experimentally challenged with the DSc pathogen had some shifts in microbial composition, but F. hongkongensis was not a part of the core bacteria in DSc-challenged specimens. DSc-affected Echinothrix diadema from Réunion Island showed a similar high representation of F. hongkongensis as that seen on Caribbean D. antillarum . Our results suggest that DSc alters Diadematidae microbiomes and that F. hongkongensis may be a candidate bacterial biomarker for DSc in environmental samples. The mechanism driving microbiome variation in host–pathogen interactions remains to be explored.

mSystems↗

USGS2025

Detection of the Diadema antillarum scuticociliatosis Philaster clade on sympatric metazoa, plankton, and abiotic surfaces and assessment for its potential reemergence

A ciliate belonging to the Diadema antillarum scuticociliatosis (DaSc)-associated Philaster clade (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 of D. antillarum tissues, 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 sym- patric 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.

Florida↗

USGS2023

A scuticociliate causes mass mortality of Diadema antillarum in the Caribbean Sea

Echinoderm mass mortality events shape marine ecosystems by altering the dynamics among major benthic groups. The sea urchin Diadema antillarum , virtually extirpated in the Caribbean in the early 1980s by an unknown cause, recently experienced another mass mortality beginning in January 2022. We investigated the cause of this mass mortality event through combined molecular biological and veterinary pathologic approaches comparing grossly normal and abnormal animals collected from 23 sites, representing locations that were either affected or unaffected at the time of sampling. Here, we report that a scuticociliate most similar to Philaster apodigitiformis was consistently associated with abnormal urchins at affected sites but was absent from unaffected sites. Experimentally challenging naïve urchins with a Philaster culture isolated from an abnormal, field-collected specimen resulted in gross signs consistent with those of the mortality event. The same ciliate was recovered from treated specimens postmortem, thus fulfilling Koch’s postulates for this microorganism. We term this condition D. antillarum scuticociliatosis.

Science Advances↗