Tracing Geographic and Molecular Footprints of Copepod Crustaceans Causing Multifocal Purple Spots Syndrome in the Caribbean Sea Fan Gorgonia ventalina

Abstract: The recent rise in ocean temperatures, accompanied by other environmental changes, has notably
increased the occurrence and spread of diseases in Octocorallia, of which many species are integral to shallow
tropical and subtropical coral reef ecosystems. This study focuses on the understanding of these diseases, which
has been largely limited to symptomatic descriptions, with clear etiological factors identified in only a fraction
of cases. A key example is the multifocal purple spots syndrome (MPSS) affecting the common Caribbean
octocoral sea fan Gorgonia ventalina, linked to the gall-forming copepods of the genus Sphaerippe, a member of
the widespread family Lamippidae. The specialized nature of these copepods as endoparasites in octocorals
suggests the potential for the discovery of similar diseases across this host spectrum. Our investigation
employed four molecular markers to study disease hotspots in Saint Eustatius, Curaçao, northwest and
southwest Cuba, and Bonaire. This led to the discovery of a group of copepod species in these varied Caribbean
locations. Importantly, these species are morphologically indistinguishable through traditional methods,
challenging established taxonomic approaches. The observed diversity of symbionts, despite the host species'
genetic uniformity, is likely due to variations in larval dispersal mechanisms. Our phylogenetic analyses
confirmed that the Lamippidae copepods belong to the order Poecilostomatoida (Copepoda) and revealed their
sister group relationship with the Anchimolgidae, Rhynchomolgidae, and Xarifiidae clades, known for their
symbiotic relationships with scleractinian corals. These results add to our understanding of the evolutionary
and ecological interactions of copepods and their hosts, and the diseases they cause, important data in a
changing climate.