Species-rich meta-communities of the diatom order Thalassiosirales in the Arctic and northern Atlantic Ocean

Abstract

The marine planktonic diatom order Thalassiosirales are used as climate proxies with reported characteristic temperate and Polar species. However, a systematic analysis of the genetic variability and species limits is lacking. Here, we combined molecular and morphological approaches to identify Thalassiosirales from 7 Beaufort Sea sea-ice samples and 27 water-column samples collected from across the Canadian Arctic at different times of the year and the Scotia Shelf, North Atlantic in spring. While many species were found in both oceanic regions, there were two distinct Thalassiosirales communities: the first from sea ice and ice-influenced water columns and the second Arctic late summer and North Atlantic spring communities. Thalassiosirales formed genetically coherent Boreal-Arctic meta-communities, inclusive of intra-specific variants. Genetic similarity between the Arctic and North Atlantic meta-communities would be reinforced by counter-clockwise dominant surface current systems. Local patterns of spatial and temporal distributions of planktonic thalassiosiroids were best explained by latitudinal gradients and phosphate and silicate concentrations, suggesting that climate-mediated changes in Arctic and North Atlantic hydrography could have a marked effect on species distribution. Our analysis also revealed a need for taxonomic revision of several species complexes reported from the region before they can be reliably used as bio-indicators.