Doctoral Programme on Marine Ecosystem Health and Conservation
 PhD Subject Catalogue Fifth Edition - 2014
Arctic pack ice ecosystems under climate change – quantifying coupling processes between sea ice and pelagic communities and predicting their future fate
PhD Code: MARES_14_10:
Mobility
  • Host institute 1: P2 - Universität Bremen
  • Host institute 2: P5 - University of Algarve
  • Host institute 3: CCMAR (Algarve); AWI - Alfred Wegener Institute for Polar and Marine Research, Bremerhaven
Research fields:
  • T1 - Future Oceans: temperature changes - hypoxia - acidifation
  • T2 - Understanding biodiversity effects on the functioning of marine ecosystems
  • T3 - Biological Invasions
Promotor(s):
  • Holger Auel
  • Gareth Pearson
  • Ester Serrao (University of the Algarve)
Contact Person and email: Holger Auel - hauel@uni-bremen.de

Subject description
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:
  • to quantify cryo-pelagic coupling processes in the marginal ice zone of Arctic Fram Strait and on the Northeast Greenland Shelf. What is the relative contribution of ice algal primary production to the nutrition of zooplankton organisms beneath the ice and how will the retreating ice cover affect pelagic communities in the Arctic?
  • to compare the physiological response of polar vs. boreal-Atlantic key species to increasing temperatures and to determine their species-specific tolerance thresholds with regard to temperature. Are boreal-Atlantic “invaders” better adapted to increasing temperatures than polar congeners and, if so, how will this affect future species composition and trophic interactions under scenarios of global climate change?
  • to establish comparative gene expression responses and transcriptional regulation of polar vs. boreal-Atlantic key zooplankton species under varying thermal regimes. These data will be integrated with physiological responses to temperature to gain insight into phenotypic differentiation in Arctic and boreal-Atlantic species that may be crucial for adaptation under climate change scenarios.
 
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
  • Auel H, Hagen W (2002) Mesozooplankton community structure, abundance and biomass in the central Arctic Ocean. Marine Biology, 140: 1013-1021
  • Auel H, Klages M, Werner I (2003) Respiration and lipid content of the Arctic copepod Calanus hyperboreus overwintering 1 m above the seafloor at 2,300 m water depth in the Fram Strait. Marine Biology 143: 275-282
  • Buchholz F, Buchholz C, Weslawski JM (2010) Ten years after: krill as indicator of changes in the macro-zooplankton communities of two Arctic fjords. Polar Biology, 33: 101-113
  • Laakmann S, Kochzius M, Auel H (2009) Ecological niches of Arctic deep-sea copepods: Vertical partitioning, dietary preferences and different trophic levels minimize inter-specific competition. Deep-Sa Research Part I, 56: 741-756
  • Leu E, Søreide JE, Hessen DO, Falk-Petersen S, Berge J (2011) Consequences of changing sea-ice cover for primary and secondary producers in the European Arctic shelf seas: Timing, quantity, and quality. Progress in Oceanography, 90: 18-32
  • Schauer U, Beszczynska-Möller A, Walczowski W, Fahrbach E, Piechura J, Hansen E (2008) Variation of measured heat flow through the Fram Strait between 1997 and 2006. In: Dickson RR, Meincke J, Rhines P (eds) Arctic-Subarctic Ocean Fluxes: Defining the Role of the Northern Seas in Climate. Springer, pp. 65-85
  • Søreide JE, Hop H, Carroll ML, Falk-Petersen S, Hegseth EN (2006) Seasonal food web structures and sympagic pelagic coupling in the European Arctic revealed by stable isotopes and a two-source food web model. Progress in Oceanography, 71: 59-87
  • Søreide JE, Leu E, Berge J, Graeve M, Falk-Petersen S (2010) Timing of blooms, algal food quality and Calanus glacialis reproduction and growth in a changing Arctic. Global Change Biology, 16: 3154-3163
  • Søreide JE, Carroll ML, Hop H, Ambrose Jr WG, Hegseth EN, Falk-Petersen S (2013) Sympagic-pelagic-benthic coupling in Arctic and Atlantic waters around Svalbard revealed by stable isotopic and fatty acid tracers. Marine Biology Research, 9: 831-850
 


Expected outcomes
The candidate is expected to publish the results of the project together with the supervisors in at least three peer-reviewed scientific articles. He/she will present the outcomes at two international conferences. Close co-operation and exchange with other established research projects at the University of Bremen and CCMAR at the University of Algarve and in the wider MARES context will ensure that the outcomes of the Ph.D. project will be recognised by the scientific community. As the effects of climate change on Arctic marine ecosystems is an issue of global concern, it is expected that the outcomes of this project will be of high relevance for a wider audience and also gain interest of the general public.

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