Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

In the Arctic, brown algae (kelps) and seaweeds are ecologically important: providing habitat, protection, and nutrients for invertebrate and vertebrate species living in nearshore environments. Migrations of biota between the North Pacific and North Atlantic Oceans have occurred periodically during Earth’s history leading to colonization of the Arctic Ocean. Around 3.5 Mya the “Great Trans-Arctic Biotic Interchange” occurred and the Laminariales order of kelp, thought to be of North Pacific origin, underwent a massive radiation and speciation event around the Arctic Ocean. Phylogenetic analysis performed on “Laminaria-like” specimens collected from six sampling locations around the Svalbard Archipelago identified both the presence of Saccharina groenlandica and Laminaria digitata. This research represents new records for the presence of S. groenlandica around the Svalbard Archipelago. S. groenlandica and L. digitata exhibit phenotypic similarities such that these two species can be difficult to tell apart in the field. In this study we have shown that the COI gene region can be used for DNA barcoding and can provide species level resolution between these two cryptic species. Prior to this study and Lund (2014), a number of biodiversity studies conducted around the Svalbard Archipelago identified the presence of L. digitata in a number of locations around the archipelago, however S. groenlandica was not identified in any of these prior studies. Phylogenetic analysis conducted here showed that all Svalbard specimens of S. groenlandica had identical COI sequences and up to 0.30% sequence diversity with S. groenlandica specimens from other parts of the Arctic Ocean. Further analysis is needed to understand the abundance of this newly recorded species around the archipelago and to investigate both the timing of arrival and mechanisms of colonization.