Abstract

Kelp ecosystems provide habitat to many ecologically and commercially important species. They are declining globally but trends are highly variable at small geographic and temporal scales. Understanding what constrains kelp distribution at a scale relevant to management efforts is thus fundamental. Here, we examined the abiotic correlates of the distribution of two dominant kelp species (Alaria esculenta and Saccharina latissima) in the Sept-Iles region (50.21 degrees N, 66.38 degrees W), Canada, in 2017 and 2018. We surveyed kelp distribution, measured abiotic conditions in two contrasting habitats (bay and outlying islands), and conducted a transplant experiment of both species between these habitats to examine kelp performance. Saccharina latissima inhabited both habitats while A. esculenta was absent from the bay. While wave exposure was similar between the bay and islands, other abiotic factors varied between habitats, potentially driving the differing kelp distributions: temperature, turbidity and sedimentation were greater in the bay, while light availability and salinity were greater around the islands. Temperature and salinity across habitats were within the tolerance limits for both species, while irradiance was near or below sub-optimal levels in the bay, suggesting that light, turbidity and sedimentation might be the main factors limiting the distribution of A. esculenta. Both transplanted kelp species grew and survived better around the islands than in the bay, suggesting that the island habitat offers better conditions. A. esculenta survived and grew in the bay, indicating that its local-scale distribution is not constrained at the early adult stage. Our results provide an understanding of current kelp distribution and possible changes related to future abiotic conditions.