James D. Reimer

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.

Coral reefs in the Atlantic have received less attention with regard to marine biodiversity research than those in the Indo-Pacific. In an overview of articles about corals or coral reefs in the journal Marine Biodiversity and its predecessor Senckenbergiana Maritima over the years 1969–2013, 35 papers concerned the Indo-Pacific and only 13 were about the Atlantic, a ratio of 2.7/1 (Hoeksema and Van der Meij 2013). Caribbean coral reefs also deserve biodiversity research attention because not all of their species have been reported yet, and these species are likely to participate in hitherto unknown interspecific associations (e.g., Thomas and Klebba 2007; Snijders and Fransen 2010; Ivanenko et al. 2017; Montano et al. 2017b) or appear to have incomplete geographical and bathymetrical distribution range information involving new records for the Atlantic (e.g., Montano et al. 2017a; Van der Loos and Prud’homme van Reine 2017).The present special issue of Marine Biodiversity on Caribbean coral reefs serves to add information on these points

Hexactinellid sponges are important members of deep-sea benthic ecosystems because they provide available hard substrate habitats for filter-feeding invertebrates. However, symbioses between hexactinellid sponges and their symbionts are poorly known. Zoantharians associated with hexactinellid sponges have been reported widely from deep-sea marine ecosystems, either on the bodies or stalks of hexactinellid sponges. Despite these records, there has been a lack of research on their diversity and phylogenetic relationships. In this study, 20 specimens associated with amphidiscophoran and hexasterophoran sponges were collected from the waters of Australia and Japan in the Pacific, and from Curaçao in the southern Caribbean, and these were examined in addition to museum specimens. Based on molecular phylogenetic analyses and morphological observations, we formally describe two new genera and three new species of Zoantharia and report several previously described species. The results suggest at least two independent origins for the symbioses between hexactinellid sponges and zoantharians. Our results demonstrate that the diversity of hexactinellid sponge-associated zoantharians is much higher than has been previously thought. The new taxa described in this work further reconfirm that the deep-sea harbours high levels of undescribed zoantharian diversity.