Abstract
The habitat formed by the Callogorgia species, with their abundance and colony sizes, provides an important refuge for a variety of brittle stars which are recognized as the epibionts of octocorals in both shallow and deep environments. In such a relationship, ophiurans benefit directly from being elevated because they facilitate their feeding by suspension, while octocorals do not seem to benefit or be harmed. During three different expeditions developed in the Colombian Pacific from 2012 to 2013 and in the Caribbean Sea during 1998 and 2012 by the INVEMAR - Marine and Coastal Research institute, different samplings were carried out on soft bottoms through trawls with an epibenthic net. For the Pacific Ocean, 33 fragments of the octocoral Callogorgia cf. galapagensis Cairns, 2018 with 178 specimens of the ophiuroid Astrodia cf. excavata (Lütken and Mortensen, 1899) were found in two stations at depths 530 and 668 m. Considering the abundance of A. cf excavata, other biological characters such as size, presence of mature gonads, and evidence of arm regeneration were also detailed. In contrast, in the Caribbean Sea, Callogorgia gracilis (Milne Edwards and Haime, 1857) was found with ophiuroids belonging to the genera Asteroschema and Ophiomitra. The octocoral Callogorgia americana (Cairns and Bayer, 2002) was also found, but without associated brittle stars. These findings constituted the first specific association reported in the Eastern Tropical Pacific, and new relationships for the Caribbean Sea. This further reflected a possible specific association between the Callogorgia and Astrodia species that needed to be further explored. Thus, the Callogorgia species and the brittle star A. cf. excavata represented new records for the Colombian Pacific Ocean and the southern Caribbean Sea.
Highlights
The structural complexity that octocorals provide in deep habitats facilitates and increases biodiversity by providing biogenic habitats for settlement and colonization by crustaceans, echinoderms, annelids, and bryozoans, among other organisms (Buhl-Mortensen et al, 2010; Watling et al, 2011; Bourque and Demopoulos, 2018)
During the deep-sea explorations carried out on the Colombian Pacific continental shelf, one species of Callogorgia and one of the brittle stars were captured in symbiotic association
The octocoral species was identified as Callogorgia cf. galapagensis Cairns, 2018 (Figures 2A,B) and the associated was the ophiuroid Astrodia
Summary
The structural complexity that octocorals provide in deep habitats facilitates and increases biodiversity by providing biogenic habitats for settlement and colonization by crustaceans, echinoderms, annelids, and bryozoans, among other organisms (Buhl-Mortensen et al, 2010; Watling et al, 2011; Bourque and Demopoulos, 2018). Callogorgia spp. and Their Brittle Stars that, when rising from the bottom, are oriented with the flow of water to maximize the capture of food from the water that flows through their polyps This is believed to benefit the diverse assembly of facultative and potentially obligated symbionts of octocorals (Buhl-Mortensen et al, 2010; Allcock and Johnson, 2019). A close relationship occurs between cohabiting species, with the interaction beginning from their juvenile stages This is thought to occur with the ophiuran Ophiocreas oedipus Lyman, 1879 that colonizes the octocoral primnoid Metallogorgia melanotrichos (Wright and Studer, 1889) when both are young and grow up together until death, with the brittle star being the only symbiont of the colony (Mosher and Watling, 2009). At least for shallow-water species such as Ophiothela mirabilis (Verrill, 1867), it has been suggested that a negative effect could exist for the coral host due to the high densities of the brittle stars (Mantelatto et al, 2016)
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