Abstract
Nephtheidae soft corals are a common component of benthic ecosystems in the Northwest (NW) Atlantic and in the Arctic, but little is known about their functional roles. Here we investigated their role as habitat for basket stars (Ophiuroidea). By examining over 4500 soft coral colonies of Drifa glomerata, Duva florida, Gersemia spp., and Pseudodrifa racemosa collected during trawl surveys in the regions of Newfoundland, Labrador and West Baffin Bay, we show that Nephtheidae soft corals are habitat for juvenile Gorgonocephalus sp. basket stars. Juvenile Gorgonocephalus sp. were found on all soft corals species, but Drifa glomerata was the soft coral species with the highest occurrence of associated juvenile basket stars (32%), with a maximum of 111 basket stars found on a single 4.8 cm tall (contracted state) colony. Individual basket star disc diameter did not change with colony height, but it varied with season for individuals found on D. glomerata. On the other hand, colony height was positively related with maximum disc diameter (D. glomerata), and presence and number of basket stars on a colony (D. glomerata and D. florida). One very young ophiuroid was found within one polyp of a D. florida colony collected in July. We also examined bottom trawl survey data from 2011-2017 from Newfoundland to Baffin Bay, and other locations in the Eastern Canadian Arctic and found that for our largest database, 45% of trawl sets that contained basket stars also contained corals, of which 67% were Nephtheidae soft corals. In this study we show that all four Nephtheidae soft coral taxa studied act as habitat for juvenile basket stars, which are conspicuous components of benthic communities in cold-water environments. Soft corals are commonly exposed and vulnerable to bottom fishing gear in the North Atlantic. We urge future studies evaluating the nature of this relationship, the potential role of soft corals as nurseries, and the potential degree of dependency/preference between basket stars and soft corals in relation to other organisms.
Highlights
The functional role of an organism can be defined as the functions provided to the ecosystem (Vaughn and Hakenkamp, 2008), such as ecosystem functions related to impacts on substrate, benthopelagic coupling, and associations with other organisms (Bell, 2008)
Since most specimens were not submitted for molecular analysis (N = 2003 specimens in total), we opted for treating the specimens in this study as Gorgonocephalus sp., but knowing that all specimens included in the molecular analysis yielded very close matches to G. arcticus
A total of 2003 ophiuroids were found on 543 colonies (12% of all examined colonies), of these only seven were brittle stars, which were found on only five colonies
Summary
The functional role of an organism can be defined as the functions provided to the ecosystem (Vaughn and Hakenkamp, 2008), such as ecosystem functions related to impacts on substrate, benthopelagic coupling, and associations with other organisms (e.g., provision of microhabitat) (Bell, 2008). Cold-water corals are well known for their habitat-provision potential, as they are often reported in association with other organisms. Gorgonians and black corals have drawn particular attention, as they can grow to large sizes and host a variety of organisms in symbiotic, parasitic, or epibiotic relationships (Wahl, 1999; Krieger and Wing, 2002; Buhl-Mortensen and Mortensen, 2004a,b, 2005; Mosher and Watling, 2009; Clippele et al, 2015; Girard et al, 2016). With the advent of imagery technologies, in situ evidence of conspicuous associations with cold-water corals have become more common. This is especially true for taxa that can attain large sizes like gorgonians, which are more noticeable from imagery than small taxa like Nephtheidae soft corals, which are relatively small (often < 15 cm tall), with flexible, soft bodies. In contrast to other octocorals, soft corals have even been considered unsuitable to host attached species (Buhl-Mortensen et al, 2010), and believed to not host symbionts, in comparison to their warm-water nephtheid counterparts (Watling et al, 2011)
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