Seasonal succession, distribution, and diversity of planktonic protists in relation to hydrography of the Godthåbsfjord system (SW Greenland)

Abstract

High-latitude fjord environments are undergoing dynamic seasonal changes, affecting spatio-temporal patterns in planktonic abundances. To investigate how physical gradients impact sub-Arctic planktonic protists (> 20 μm), a seasonal transect study was performed in 2013 during three periods of planktonic succession: spring, summer, and autumn. The samples were collected from the glacier-fjord-ocean transect in SW Greenland using two complementary sampling methods, i.e. net hauls (20-μm net) and Niskin bottles. The key drivers of the distribution of planktonic groups and dominant taxa were hydrographic properties (defined as ‘time’, salinity, and temperature) reflecting the area’s seasonally changing circulation system. Cold and relatively saline waters in spring favoured the single haptophyte species Phaeocystis cf. pouchetii, while in summer, fresher waters influenced by glacial discharge favoured diatoms, followed by dinoflagellates and predatory ciliates in autumn. Our findings reveal a monodominant structure among the planktonic protists observed in each key sub-region and in each season. (1) Gedaniella boltonii (spring) was associated with inner fjord upwelling, (2) Chaetoceros sp. (summer) and Chaetoceros cf. socialis (autumn) were linked to ‘glacial meltwater’ circulation in the main fjord, and (3) Thalassiosira poroseriata (summer) and Skeletonema sp. (autumn) characterized warm and relatively saline offshore waters influenced by the West Greenland Current. The observed spatio-temporal patterns were linked to changes in hydrographic regimes driven by the interplay between the melting of the Greenland Ice Sheet and inflows of offshore, Atlantic-sourced waters.