Structuring of polar phytoplankton communities by glacial meltwater input: an overview

By Prof.dr. A.G.J. Buma
Ocean Ecosystems, Energy and Sustainability Research Institute Groningen, University of Groningen

Single celled phytoplankton form the foundation of polar marine food webs. The productivity of polar phytoplankton is highly restricted in space and time. Typically, phytoplankton blooms may occur in frontal areas and along the retreating ice edge. Yet, they primarily develop in coastal areas, where they may support a high biological richness. However, surface waters in Arctic and Antarctic coastal regions undergo increasing physical and chemical alterations during summer, due to the observed retreat in coastal glaciers. The associated effluxes of glacial meltwater, enriched in sediments, may lead to decreased surface salinity, enhanced surface stratification, increased turbidity and decreased light penetration. We hypothesized that these changes affect the dynamics and composition of marine phytoplankton communities, mainly through changes in light and nutrient availability. Spring and summer variability in marine phytoplankton performance was investigated as a function of meltwater discharge at four polar locations: two adjacent Arctic fjords (Kongsfjord, Krossfjord, West-Spitsbergen, IPY), and two locations along the Western Antarctic Peninsula (WAP): Potter Cove, (King George Island: ESF PolarClimate) and the Pine Island Bay (Amundsen Sea, NAAP). Phytoplankton data were coupled to meltwater indicators, such as CTD profiling of salinity, temperature, density and light attenuation, as well as macronutrient (N, P, Si) availability. Phytoplankton community composition was assessed by pigment and molecular fingerprinting (HPLC and DGGE) followed by key species identification based on 18S rDNA sequencing. Furthermore, standard biomass, primary production and physiological indicators were included.
The two Arctic fjords were found to differ in phytoplankton composition. After the spring bloom, dominated by diatoms and Phaeocystis sp. a community shift was observed close to the glacier in the Kongsfjord, in favor of small sized phytoplankton species, coinciding with enhanced surface stratification and sediment load. These effects were less pronounced in the Krossfjord. Overall, post-bloom conditions prevailed in both fjords, and macro-nutrient limitation regulated the limited phytoplankton performance in both fjords during summer. At the Potter Cove location, meltwater input did not seem to affect phytoplankton community structure, based on a preliminary data set. Here, exposure to the prevailing high wind speeds seems to prevent surface stratification during the summer months. As a result, macronutrient levels remain high throughout whereas phytoplankton biomass remains low. Yet, the low light penetration close to the glacier discharge locations was found to affect phytoplankton physiological parameters, in particular photoacclimation properties. The Pine Island Bay (Amundsen Sea) location was found to be strongly affected by glacial meltwater input. Here, meltwater discharge was found to enhance surface stratification and nutrient (notably Fe) availability, thereby facilitating phytoplankton bloom formation, in particular of Phaeocystis sp.
Although large differences in meltwater responses were observed, our results suggest that alterations in productivity, physiology and composition of marine microbial communities may follow from enhanced glacier melting. Possible consequences for marine food web structure will be discussed.

Willem Barentsz Poolinstituut

Bundeling van kennis, onderzoek en onderwijs over de Noord- en de Zuidpool

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