Abstract
Deep-water sedimentary habitats off Nova Scotia have only rarely been explored. The topographically and oceanographically complex shelf of Nova Scotia harbours two interesting topographic features, Emerald Basin, a sedimentary habitat reaching greater depths (max of 270 m) than the surrounding shelf and the Gully, the largest canyon in NW Atlantic. Emerald Basin is exposed to upwellings of slope water and harbours predominantly deep-sea hexactinellid sponges. Such distributional pattern resembles “deep-water emergence”. In this study an abundant benthic group, the polychaetes, were selected to test for such deep-water faunal link. Qualitative boxcores were collected from Emerald Basin (180 m depth, N = 5) and the adjacent Gully Canyon (1600 m, N = 3). At species level, there was no overlap in distribution between Emerald Basin (N = 73, S=29) and Gully Canyon (N = 351, S = 60) fauna based on morphological assessment of all specimens and molecular analysis (COI and 16S markers) of selected morphotypes. In an alternative approach, Multivariate analysis (nMDS, Cluster Analysis) of incidence data for polychaete genera (N = 179) from 24 Atlantic sites (5–1600 m) was carried out. These results showed a greater similarity of Emerald Basin polychaetes to bathyal sites (400–1000 m), particularly the 680 m site off Nova Scotia rather than shelf sites (5–80 m), including those on the Nova Scotia shelf. Thus, at 1600 m, the Gully Canyon samples were likely “too deep” for our comparative purposes and depths of < 1000 m should be targeted in the future.Our data also provide the first published assessment of polychaete diversity from the Gully Canyon, suggesting the presence of a diverse assemblage (S = 60). Unusually for a deep-sea site, the Gully Canyon polychaetes are mostly known taxa with wider distribution across bathyal NW Atlantic. Additionally, our molecular data provide an interesting insights into the distribution of several polychaete species commonly found in deep-sea (e.g Aurospio dibranchiata Maciolek, 1981; Ophelina abranchiata Støp-Bowitz, 1948) suggesting wide geographical distribution for some but revealing species complexes for others.
Highlights
Soft sediments of the deep-sea represent the largest, and least explored habitat on the planet (e.g. Gage and Tyler, 1991; Snelgrove, 1997; Glover et al, 2010)
From Emerald Basin, 73 specimens were collected in total, with majority from the boxcores (N = 68), with five additional specimens from the remotely operated vehicle (ROV) biobox belonging to the representatives of species found in boxcores
The greatest number of both individuals and species was contributed by 500 μm mesh size (N = 53 and S = 25 for Emerald Basin; N = 215 and S=48 for Gully Canyon) (Fig. 2)
Summary
Soft sediments of the deep-sea represent the largest, and least explored habitat on the planet (e.g. Gage and Tyler, 1991; Snelgrove, 1997; Glover et al, 2010). Soft sediments of the deep-sea represent the largest, and least explored habitat on the planet Gage and Tyler, 1991; Snelgrove, 1997; Glover et al, 2010) These soft sediments represent an ideal habitat for polychaete worms, an important component of benthic macrofauna worldwide in terms of numbers of individuals and species, as well as diversity of functional groups Understanding the diversity and distribution of polychaetes can significantly contribute towards the knowledge of deep-sea ecology. Glasby and Alvarez, 1999) This is considered an artefact of poorly understood taxonomy, and a tendency to “lump” morphologically similar species together, leading to wide geographic and/or bathymetric ranges for some species. Molecular methods have provided new tools for taxonomists, often revealing species complexes (see Nygren, 2014 for review), but in rare cases the wide distributions of polychaete species have been confirmed (e.g. Ahrens et al, 2013; Georgieva et al, 2015; Paxton et al, 2017)
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