Seasonal microbial processes in a high-latitude fjord (Kongsfjorden, Svalbard): I. Heterotrophic bacteria, picoplankton and nanoflagellates

Abstract

Temporal dynamics of the microbial food web in the Barents Sea and adjacent water masses in the European Arctic are to a large extent unknown. Seasonal variation in stocks and production rates of heterotrophic bacteria and phototrophic and heterotrophic picoplankton and nano-Xagellates was investigated in the upper 50 m of the highlatitude Kongsfjorden, Svalbard, during six Weld campaigns between March and December 2006. Heterotrophic bacteria, picoplankton and nanoXagellates contributed to ecosystem structure and function in all seasons. Activity within the microbial food web peaked during spring bloom in April, parallel to low abundances of mesozooplankton. In the nutrient-limited post-bloom scenario, an eYcient microbial loop, fuelled by dissolved organic carbon from abundant mesozooplankton feeding on phytoplankton and protozooplankton, facilitated maximum integrated primary production rates. A tight microbial food web consisting of heterotrophic bacteria and phototrophic and heterotrophic picoplankton and nanoXagellates was found in the stratiWed water masses encountered in July and September. Microbial stocks and rates were low but persistent under winter conditions. Seasonal comparisons of microbial biomass and production revealed that structure and function of the microbial food web were fundamentally diVerent during the spring bloom when compared with other seasons. While the microbial food web was in a regenerative mode most of the time, during the spring bloom, a microbial transfer mode represented a trophic link for organic carbon in time and space. The microbial food web's ability to Wll diVerent functional roles in periods dominated by new and regenerated production may enhance the ecological Xexibility of pelagic ecosystems in the present era of climate change.

Organic carbon flux and particulate organic matter composition in Arctic valley glaciers: examples from the Bayelva River and adjacent Kongsfjorden

“…The physical and biological characteristics of Kongsfjorden have been summarized by Hop et al (2006). Nitrogen limitation of primary production occurs during summer months (Rokkan Iversen and Seuthe, 2011), when stratification of the water column and input of nutrient-depleted glacial meltwater results in oligotrophic surface water in the inner fjord (e.g., increase proportion of cyanobacteria and cryptophytes in surface phytoplankton communities; Hop et al, 2002). Moreover, where turbid meltwater has yet to mix with clear sea water, phytoplankton growth is limited by reduced illumination (Svendsen et al, 2002).…”

Spring bloom dynamics in Kongsfjorden, Svalbard: nutrients, phytoplankton, protozoans and primary production

“…Only a few primary production measurements have been published from Kongsfjorden (Eilertsen et al 1989;Hop et al 2006;Piwosz et al 2009;Rokkan Iversen and Seuthe 2010) and only one from spring (Rokkan Iversen and Seuthe 2010). Our primary production measurements contribute with a considerable increase in time resolution for this important period of the year.…”

“…Either it will be grazed and recycled in the upper water masses or it may sink to deeper waters (Wassmann 1998). Recent research has also emphasized the importance of nanoplankton and picoplankton (Lovejoy et al 2007;Sakshaug et al 2009;Rokkan Iversen and Seuthe 2010) and showed that the concept of short, low-diversity polar food chains is overly simplistic (Smetacek and Nicol 2005).…”

“…In general, quantitative data on production, biomass and consumption of phytoplankton were lacking from the pelagic ecosystem in Kongsfjorden. Several later studies have focused on some of these gaps and provided information about phytoplankton species (Okolodkov et al 2000;Wiktor and Wojciechowska 2005;Leu et al 2006;Hegseth and Tverberg 2008;Piwosz et al 2009;Wang et al 2009;Rokkan Iversen and Seuthe 2010;Seuthe et al 2010), on bacterial abundances and communities (Janowska et al 2005;Piquet et al 2010;Rokkan Iversen and Seuthe 2010) and on zooplankton (Basedow et al 2004;Hagen 2005, 2007;Willis et al 2006;Narcy et al 2009;Walkusz et al 2009). Basic information about primary production in Kongsfjorden is limited and only few measurements have been published (Eilertsen et al 1989;Hop et al 2002;Piwosz et al 2009;Rokkan Iversen and Seuthe 2010).…”

Effects of prolonged darkness and temperature on the lipid metabolism in the benthic diatom Navicula perminuta from the Arctic Adventfjorden, Svalbard

“…The water masses in the Svalbard fjords are in the winter months well mixed with water temperatures ranging between −1.2 and 1.5 °C (Iversen and Seuthe 2011;Pawłowska et al 2011). Signals of a warming Arctic as reflected in raised surface air temperatures, a retreat and thinning sea ice cover, a longer melt season and increasing river discharges are observed since the 1980s (Serreze and Francis 2006;IPCC 2007;Bintanja and van der Linden 2013).…”