Abstract
As a contribution to understanding the ecological framework of protistan seasonal succession patterns, we present the weekly-to-monthly (January–October) light microscopy-based study of nano- and microplanktonic protist communities of Adventfjorden waters in 2013. In general, protist dynamics corresponded to the classic paradigm for the Arctic ice-free waters with extremely low abundance and diversity in winter, with the main abundance and chlorophyll-a peak in April-May, followed by a diverse but low abundant community during summer/autumn. However, the reference of the obtained data to the previously conducted year-round research in 2012 allows us to observe substantial variability in seasonal patterns between the two consecutive years. The most striking difference concerned the spring bloom composition and abundance, with clear domination of Phaeocystis pouchetii in Atlantified fjord waters in 2012 and Bacillariophyceae-dominated (mainly Fragilariopsis, Thalassiosira nordenskioeldii, and, in a lesser extent, also Pseudo-nitzschia seriata) bloom in 2013 when local water prevailed. On the other hand, a surprisingly high share of spring bloom taxa persisted throughout the summer/autumn of 2013 when they co-occurred with typical summer taxa (dinoflagellates and other small flagellates). Their extended growth could, at least in part, result from scarce Ciliophora throughout the season, which, in turn, can be attributed to the high grazing pressure of very numerous meroplankton and mesozooplankton. In light of this, our results may be relevant in discussions proposed for the West Spitsbergen waters link between the Atlantic water inflow and the spring bloom composition, as well as its further progression in the productive season. They also highlight the strong need for further high-resolution monitoring of annual plankton cycles and great caution when looking for phenological patterns within a single year or when interpreting short-term data.
Highlights
Protist communities, at high latitudes, show strong seasonal shifts in qualitative and quantitative compositions associated with light conditions, ice cover, water masses, nutrient availability and grazing pressure
We address the identification of possible differences and similarities in protist dynamics between the two consecutive years with different oceanographic conditions (2012 vs. 2013) to contribute to the discussion on the already proposed impact of Atlantic water (AW) waters on West Spitsbergen protists phenology
In contrast to the virtually completely Phaeocystis-dominated spring bloom in 2012, when AW dominated in the fjord, spring bloom in 2013 when local water prevailed was mainly composed of Bacillariophyceae
Summary
At high latitudes, show strong seasonal shifts in qualitative and quantitative compositions associated with light conditions, ice cover, water masses, nutrient availability and grazing pressure. Protists are critically important for the functioning of marine ecosystems as primary producers and consumers of carbon and maintainers of biogeochemical cycles [1] Despite their unquestionable importance, little is known about their seasonal dynamics in the Arctic waters [2]. Its side branches (such as the Adventfjorden located on the southern shore of Isfjorden) can experience strong freshwater inputs from glacial rivers every summer and autumn [6] These inputs bring sediments, nutrients and organic matter across the land–ocean interface, with a range of implications for coastal ecosystems and biogeochemical cycling [7]. Isfjorden is recognised as a representative system to follow ocean climate change in the Arctic Ocean and, in that way, be used as an indicator for climate change in its Eurasian part [8]
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