Spatio-temporal mapping of neritic benthic assemblages in sub-Arctic marine ecosystems

Marine benthic assemblages tend to express spatio-temporal patterns, but mapping of benthic environments rarely addresses temporal aspects. To understand the spatial distribution of benthic assemblages, in situ samples (ground-truthing)—often using image and/or video data—can be combined with spatially continuous acoustic layers to predict full-coverage maps. However, most studies are built from a single ground-truthing event, making these maps a simple snapshot of the distribution of organisms without temporal variability. To address this limitation, we recorded seasonal benthic video of a sub-Arctic Bay in Newfoundland and Labrador, Canada, to describe the spatio-temporal changes that occurred in benthic communities across seasons. Biotic assemblage data were associated with environmental data layers derived from previously collected bathymetry and backscatter data to predict spatially continuous season-specific community maps. The predicted assemblages exhibited seasonal variability, reflecting differences in densities and locations of individual species. The most pronounced assemblage change was driven by the widespread disappearance of the most abundant species, the fuzzy sea cucumber Psolus cf. phantapus , in fall and winter. This species reduced in density from a peak of 2.955 m -2 in spring to <0.02 m -2 over fall and winter. The importance of the environmental data layers in explaining the difference between the assemblages varied across seasons despite these input layers being static. Without the incorporation of spatio-temporal dynamics into community studies, entire species can be missed or misrepresented. Capturing the natural fluctuations of sub-Arctic coastal ecosystems will be crucial in the early detection of perturbations caused by climate change.