Factors that influence the distribution of the Arctic endemic kelp, Laminaria solidungula (J. Agardh 1868)

Abstract

Foundation species, including kelps, have a disproportionate effect on ecosystems by exerting strong influence on food webs and community structure. Shifts in kelp species’ distributions are occurring worldwide, and are especially anticipated in the Arctic due to habitat modification by climate change. On Arctic inner shelves, the kelp Laminaria solidungula (J. Agardh 1868) can dominate nearshore rocky areas, and provide physical structure and subsidies of year-round primary production in a highly seasonal region. However, controls over the distribution of this Arctic endemic species are not well understood. A species’ interactions with the abiotic and biotic environment, its dispersal dynamics, and evolutionary history all control its ultimate range and spatial arrangement. This work describes how these factors impact L. solidungula distribution across multiple scales, with focus on the Stefansson Sound Boulder Patch, Beaufort Sea, Alaska. First, although the Stefansson Sound open-water season has lengthened by ~17 days since 1979, annual kelp growth shows no long-term trends because attenuation by suspended sediments causes pervasive low-light conditions during summer (mean light attenuation: 0.5-0.8 m⁻¹), negating any positive impacts of decreased ice-cover. Second, the abiotic environment of the Boulder Patch undergoes significant seasonal changes, mediated by physiography and bathymetry, which impact the spatial arrangement of L. solidungula and other epilithic species. A site within 4 km of river inputs experiences salinity drops of ~30 corresponding to the spring freshet. Crustose coralline algae (0-19% average cover) is completely absent at this site, but cover increases with distance from river inputs. Red algae (47-79%) and kelp (2-19%) cover shows no clear environmental correlations, and are likely regulated by multiple factors. Importantly, no L. solidungula recruited to settlement tiles after three years of deployment. Finally, population genetics suggest Beaufort Sea L. solidungula is one large interbreeding population (population differentiation as global F[subscript ST]: 0.01) assisted by the regional current regime, though smaller scale differentiation occurs within the Boulder Patch. Additionally, Beaufort Sea L. solidungula is genetically distinct from those in other areas of the Western Arctic Ocean Basin. This work represents an important baseline in ecological and genetic characteristics of L. solidungula in the rapidly changing Arctic Ocean