Between a rock and a hard place: experimental assessment of recruitment patterns in a bathyal environment of the Low Arctic.

The study of larval transport and recruitment in the deep sea is crucial to the understanding of species distributions, community assembly, and the potential effects of anthropogenic activity and climate change on the maintenance of biodiversity. This study sought to better understand the role of substratum features in deep-sea larval recruitment at high latitudes. Four settlement frames composed of blocks of different substrata (mesh, plastic, stone, and wood) were deployed for 9 to 13 months at bathyal depths in the Labrador Sea (northeastern Canada). Colonial hydrozoans dominated as recruits, with one taxon (family Campanulariidae) colonizing all substratum types across all geographic sites. Other taxa, including arthropods, octocorals, and other anthozoans recruited only onto specific substrata and consistent microhabitats within them. Overall, higher morphospecies and phylum richness characterized the three-dimensional mesh substratum relative to other substratum types, whereas the complex surface area offered by projections in the plastic substratum had higher densities of individuals or colonies for all morphospecies combined. Wood, offered as a single elongated panel, was the most heavily colonized, whereas both mesh and stone hosted morphospecies not found on any other substratum type. Factors such as geographic location, depth, altitude above the sea floor, and orientation/obstruction of the frame, may have modulated recruitment patterns. These results provide foundational knowledge on larval recruitment patterns and early colonization by opportunistic hard-bottom benthic taxa in a poorly-studied region of the Eastern Canadian deep sea.