Fatty acid dynamics during the spring bloom in a High Arctic fjord: importance of abiotic factors versus community changes

Abstract

We followed the fatty acid composition of particulate organic matter (POM) in a High Arctic fjord (79°N; Svalbard, Norway) during and after the spring bloom. The content of essential polyunsaturated fatty acids (PUFAs) was highest (45% of total fatty acids) at the beginning of the bloom, well before the biomass maximum, and decreased linearly towards the end (30%). During the postbloom period, the concentrations of PUFAs remained stable, between 25% and 30%. Redundancy analysis was used to identify the environmental factors that explained the observed variability in the fatty acid composition of phytoplankton. A particular emphasis was put on the potential influence of high irradiances. During the spring bloom, nutrient availability (Si and N), as well as shifts in phytoplankton community composition and chlorophyll a, were shown to account for much of the pattern in fatty acid composition. During the postbloom period, particularly during periods of stratification, light had a pronounced effect on the fatty acid composition. In general, we found a decrease in the relative amount of PUFAs under high light intensities and nutrient limitation.Résumé : Nous avons suivi la composition en acides gras de la matière organique particulaire (POM) dans un fjord du haut-arctique (79EN, Svalbard, Norvège) avant et après la prolifération printanière des algues. La concentration d'acides gras polyinsaturés (PUFA) essentiels est maximale (45 % des acides gras totaux) au début de la période de proliféra-tion, bien avant le maximum de biomasse; elle décline ensuite linéairement jusqu'à la fin (30%). Durant la période qui suit la prolifération, les concentrations de PUFA restent stables, à 25-30 %. Une analyse de redondance permet d'identifier les facteurs du milieu qui expliquent la variabilité observée de la composition en acides gras du phytoplancton. Nous nous intéressons en particulier au rôle potentiel des fortes irradiations. Durant la prolifération printanière, la disponibilité des nutriments (Si et N), de même que les changements de composition de la communauté phytoplanctonique et de la chlorophylle a, expliquent en grande partie les patrons de composition en acides gras. Après la prolifération, surtout durant les périodes de stratification, la lumière a un effet marqué sur la composition en acides gras. En général, il se produit une diminution de la quantité relative de PUFA dans les conditions de fortes intensité lumineuse et de limitation des nutriments.[Traduit par la Rédaction] Leu et al. 2779

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

“…From the studies presented in Table 4, we argue that the timing and intensity of the spring bloom in the fjord vary considerably among '' years (2002-2004), there were observed differences in stabilization of the water column. In 2003, when the spring bloom was delayed to May no thermal stratification developed before late May (Leu et al 2006). We therefore hypothesize that meteorological factors have a large impact on the timing of the spring bloom in years, when the fjord is dominated by Arctic water.…”

“…Photoinhibition could also be an explanation but Leu et al (2006) showed that when the water column was homogenous the phytoplankton cells did not stay in the surface layer long enough to suffer from photodamage. Episodic events of stormy weather and following intrusion of nutrients from deeper water masses might have maintained primary production until 13 May, after which it remained very low.…”

“…It is unlikely that the biomass was from deep primary production but rather is a result of sinking phytoplankton. Also in the years 2003, 2006 and 2007, the biomass of phytoplankton was assumed to be vertically exported (Leu et al 2006;Hegseth and Tverberg 2008;Narcy et al 2009). Based on these conclusions (high primary production, only moderate grazing and observed sinking biomass), we hypothesize that a large part of the primary production during the peak of the bloom is vertically exported.…”

“…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).…”

The fate of dietary lipids in the Arctic ctenophore Mertensia ovum (Fabricius 1780)

“…The increase in the trophic marker fatty acid 18:4(n-3) clearly shows the changes in the lipid composition of the prey, changing from a spring to a more summer/autumn-like signature in both phyto-and zooplankton (Kattner et al 1989;Leu et al 2006). This is probably accompanied by a change in copepod composition from the dominance of Calanus glacialis to C. Wnmarchicus, associated with advection of transformed Atlantic water masses into the fjord (Basedow et al 2004;Willis et al 2006).…”