Viral metagenomic investigation of two Caribbean echinoderms, (Echinoidea) and (Holothuria).

BACKGROUND

Echinoderms play crucial roles in coral reef ecosystems, where they are significant detritivores and herbivores. The phylum is widely known for its boom and bust cycles, driven by food availability, predation pressure and mass mortalities. Hence, surveillance of potential pathogens and associates of grossly normal specimens is important to understanding their roles in ecology and mass mortality.

METHODS

We performed viral surveillance in two common coral reef echinoderms, and , using metagenomics. Urchin specimens were obtained during the 2022 scuticociliatosis mass mortality event from the Caribbean and grossly normal specimens from a reef in Florida. Viral metagenomes were assembled and aligned against viral genomes and protein encoding regions. Metagenomic reads and previously sequenced transcriptomes were further investigated for putative viral elements by Kraken2.

RESULTS

was devoid of viruses typically seen in echinoderms, but yielded viral taxa similar to those found in other sea cucumbers, including (Picornaviruses), (Bunyaviruses), and (Nodaviruses). The lack of viruses detected in may be due to the large amount of host DNA in viral metagenomes, or because viruses are less abundant in tissues when compared to tissues. Our results also suggest that RNA amplification approach may influence viral representation in viral metagenomes. While our survey was successful in describing viruses associated with both echinoderms, our results indicate that viruses are less pronounced in than in other echinoderms. These results are important in context of wider investigation on the association between viruses and mass mortalities, since the conventional method used in this study was unsuccessful.