Background

The Arctic Ocean and adjacent ice-covered seas are the areas most rapidly and strongly affected by global warming over the coming decades. Within one or two human generations, we will witness principal changes in the extent, thickness and seasonal coverage of sea ice, strongly affecting not only ice-associated biota, but also pelagic communities beneath the ice.

 

Physical oceanographic studies in Arctic Fram Strait revealed an increasing Atlantic inflow via the West Spitsbergen Current (Schauer et al. 2008). Repetitive analyses of zooplankton community structure demonstrate substantial changes in species composition and biodiversity between the 1990s and 2006, both in Fram Strait and in Svalbard fjord systems (Laakmann et al. 2009, Buchholz et al. 2010). Boreal-Atlantic species have shifted in distribution further north and now dominate plankton communities in Fram Strait. These changes will have a strong impact on secondary productivity of Arctic seas, pelagic-benthic coupling processes and sedimentation rates (Auel et al. 2003). However, different components of polar food webs might react differently to climate change and increasing Atlantic inflow. Based on model calculations, a mismatch in the timing of the phytoplankton bloom and the seasonal ascent of the dominant copepod Calanus hyperboreus from its hibernation depth could disrupt pelagic food chains and lead to a system dominated by microzooplankton that would not support higher trophic levels and fisheries. In contrast, other studies predict an increased zooplankton production and a better food supply for pelagic fish in conjunction with warmer sea surface temperatures. Thus, present predictions are still highly controversial and the effects of an increasing Atlantic inflow on pelagic biodiversity and productivity represent key questions for future ecological research in the Arctic (Leu et al. 2011, Søreide et al. 2010).

 

Ice-covered polar seas strongly differ from other oceanic ecosystems by the fact that a large fraction of total primary production is provided by ice algae living in the microscopic brine channel system within sea-ice floes. They can contribute more than a third of total primary production (Søreide et al. 2013). Thus, ice algal production, exchange processes and trophic interactions between the sea-ice community and the pelagic realm are the key for our understanding of Arctic marine food webs (Auel & Hagen 2002). Further studies on the physiological and ecological response of key species to ocean warming and an increasing Atlantic inflow are urgently needed to assess and forecast potential impacts of global change on marine pelagic ecosystems in Arctic seas.

 

Objectives

The proposed MARES project will cover three objectives:

 

Work programme

The proposed MARES project will be tailored around the AMICA 2016 (Arctic Marginal Ice zone Community Assessment) research cruise onboard R/V Polarstern to Fram Strait and the Northeast Greenland Shelf in summer 2016. During the cruise, pelagic and sea ice organisms will be sampled for trophic biomarker analyses (stable isotopes, fatty acids; Søreide et al. 2006) in order to quantify the contribution of ice-algal vs. phytoplankton primary production (objective 1). In addition, respiration measurements will be conducted onboard by optode respirometry with polar vs. boreal-Atlantic key zooplankton species under different temperature regimes in order to study their physiological response and to determine species-specific thresholds. Experiments will focus on pairs of congeners with polar vs. boreal-Atlantic origin, i.e. the copepods Calanus glacialis and C. hyperboreus vs. C. finmarchicus, the amphipods Themisto libellula vs. T. abyssorum and T. compressa, and the krill species Thysanoessa inermis vs. T. longicaudata (objective 2). Additional experimental samples will be collected and preserved for transcriptomic analyses. Sampling effort will be concentrated on treatments in physiological experiments that reveal phenotypic variation between polar and boreal-Atlantic species. Total RNA will be extracted from selected species and used for RNAseq. Generation of de novo transcriptome assemblies and subsequent bioinformatic analysis (functional annotation, gene expression) will be performed at Ualg (objective 3). 

The Universities of Bremen (UniHB) and of the Algarve (UAlg) will join their complementary expertises for this research project. UniHB will be responsible for field work, ecophysiological experiments and ecological studies, whereas UAlg will contribute the genetic part of the project. The project shall start at the end of 2015 or in early 2016. The first six months will be used for training purposes and preparation of the research cruise, which will take place in summer 2016. Thereafter, the candidate will analyse the zooplankton samples in Bremen and spend at least six months at UAlg for transcriptome analysis. 

 

References