Diatom biogeography from the Labrador Sea revealed through a trait-based approach

Diatomsare a keystone algal group, with diverse cell morphology and a global distribution. The biogeographyof morphological, functional and life-history traits of marine diatomswere investigated in Arctic and Atlantic waters of the Labrador Sea during the spring bloom(2013-2014). In this study, trait-based analysis using community-weighted means showed that low temperatures (<0oC) in Arctic waters correlated positively with diatomspecies that have traits such as low temperature optimum growth and the ability to produced ice-binding proteins, highlighting their sea-iceorigin. High silicate concentrations in Arctic waters, as well as sea-icecover and shallow bathymetry, favoured diatomspecies that were heavily silicified, colonial and capable of producing resting spores, suggesting that these are important traits for this community. In Atlantic waters, diatomspecies with large surface areato volume ratioswere dominant in deep mixed layers, whilst low silicate to nitrate ratios correlated positively with weakly silicified species. Sharp cell projections, such as processes or spines, were positively correlated with water-column stratification, indicating that these traits promote positive buoyancy for diatomcells. Our trait-based analysis directly links cell morphology and physiology with diatomspecies distribution, highlighting allowing new insights on how this method can potentially be applied to explain ecophysiologyand shifting biogeographical distributions in a warming climate.