Journal article Open Access

Glass sponge grounds on the Scotian Shelf and their associated biodiversity

Hawkes, Nickolas; Korabik, Michelle; Beazley, Lindsay; Rapp, Hans Tore; Xavier, Joana R; Kenchington, Ellen

Emerald Basin on the Scotian Shelf off Nova Scotia, Canada, is home to a globally unique population of the glass sponge Vazella pourtalesi. Through the analysis of both in situ photographs and trawl catch data from annual multispecies bottom-trawl surveys, we examined community composition, species density, and abundance of epibenthos and fish associated with V. pourtalesi compared to locations without this sponge. Using generalized linear models and analysis of similarities, the importance of V. pourtalesi in enhancing species density and abundance of the associated epibenthic community was assessed against that of the hard substrate on which it settles. Our results indicated that the megafaunal assemblage associated with V. pourtalesi was significantly different in composition and higher in species density and abundance compared to locations without V. pourtalesi. Analysis of similarity of trawl catch data indicated that fish communities associated with the sponge grounds are significantly different from those without V. pourtalesi, although no species were found exclusively on the sponge grounds. Our study provides further evidence of the role played by sponge grounds in shaping community structure and biodiversity of associated deep-sea epibenthic and fish communities. The mechanism for biodiversity enhancement within the sponge grounds formed by V. pourtalesi is likely the combined effect of both the sponge itself and its attachment substrate, which together comprise the habitat of the sponge grounds. We also discuss the role of habitat provision between the mixed-species tetractinellid sponges of the Flemish Cap and the monospecific glass sponge grounds of Emerald Basin.

ACKNOWLEDGEMENTS. This work was funded in part through the SponGES—Deep-sea Sponge Grounds Ecosystems of the North Atlantic: an integrated approach towards their preservation and sustainable exploitation, under H2020 - the EU Framework Programme for Research and Innovation (Grant Agreement no. 679849) where Fisheries and Oceans Canada (DFO) is a third-party participant. This research was funded in part through the DFO Strategic Program for Ecosystem-Based Research and Advice (SPERA) project 'Evaluation of the Effectiveness of Two Sponge Conservation Areas in the Maritimes Region: Identifying Patterns of Dispersal, Connectivity, and Recovery Potential of the Russian Hat Sponge Vazella pourtalesi' led by L. Beazley. We thank C. Lirette (DFO) for the extraction and preparation of data from the multispecies trawl survey database, and Dr. F.J. Murillo and Dr. R. Stanley (DFO) for providing com- ments on an earlier version of this manuscript.
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