Where’s my dinner? Do Arctic benthic communities show preferential food uptake?

The Arctic is changing rapidly in response to a warming global climate, with a reduction in sea-ice coverage providing the most obvious indicator. However, the impact of this reduction in sea- ice on water column and seafloor ecology is much less certain. Changing physical conditions potentially impacts on the timing, magnitude and distribution of both ice algae and pelagic primary production(1,2) with as yet unresolved effects on trophic pathways which support both pelagic and benthic consumers(3). The recently funded NERC Arctic PRIZE project (Arctic PRoductivity in the seasonal Ice ZonE) aims to determine how these sea ice changes will affect biological and biogeochemical systems in this climatically-sensitive region.

As late spring approaches, ice-algae dissociates from underneath the ice and sinks rapidly to the seafloor providing a sudden and large input of food to the benthic community underneath. Pelagic phytoplankton production starts only once sea-ice has started to melt leading to a temporal discontinuity between sea-ice and open-water production. Using fatty acid biomarkers researchers have found that the relative amounts of diatoms/dinoflagellates/bacteria in ice particulate organic matter (POM) differed from pelagic POM and that it changed seasonally within pelagic POM(4). Pelagic grazing pressure in the Arctic is relatively low compared to temperate systems, thus the benthic fauna tend to receive a greater fraction of available organic material from the sea-ice algae and respond quickly to this input by utilising it for growth/reproduction before it is lost through burial within the sediment(5,6).

Much of the recent work undertaken has focussed on the uptake of ice algae versus phytoplankton by zooplankton, pelagic fauna and larger mammals, with relatively little research on benthic communities. Some recent studies investigated the macrobenthic communities around northern Svalbard from samples collected in 2003/2004(3). They studied the uptake of sympagic algae versus phytoplankton by the benthos in the region using stable isotopes and fatty acid tracers. Initial results suggest that the benthic community feeds primarily on ice algae and that with high proportions of diatom fatty acid trophic biomarkers implying that the benthic fauna are selectively retaining high quality food. The exception are suspension feeders as they also appear to utilise the phytoplankton as a food source.

By using stable isotopes, fatty acid tracers and a new technique using highly branched isoprenoid lipid markers(7) the aim will be to quantify the relative composition of phytoplankton vs ice-algae consumed and determine the composition of organic carbon stored in sediments and consumed by the fauna. The subsequent combination of H-Print and δ15N will provide quantitative estimates of how sea-ice organic carbon becomes distributed within the food web.
Hypothesis: Benthic communities (meiofauna through to macrofauna) preferentially feed on ice-algae as opposed to phytoplankton.

The student will participate in Arctic PRIZE research cruises and collect samples using trawls and corers in deeper northern Svalbard waters. Faunal identification to lowest possible taxonomic level will be undertaken between SAMS, Akvaplan-niva and UiT. Stable isotope analysis will be undertaken in conjunction with the NERC Mass Spectrometry Facility, whilst the H-Print analysis will allow for greater certainty as to what the fauna are preferentially feeding upon. Total lipids will provide a measure of level of nutrition as its composition is an important measure of the condition of an organism and its value as a food source. This analysis will be undertaken at the facilities in SAMS. Interpretation and analysis of remote sensing data will be undertaken in conjunction with the University of Strathclyde.

The student will also be expected to disseminate and publish their work. The student will attend final year undergraduate modules in "Deep-Sea Ecosystems” as well as “Polar Seas" that covers many of the theoretical and practical components of the work. They will also, depending on recruitment start date participate in the Ecology of Arctic Marine Benthos Course (AB-821) run by the University Centre in Svalbard, with whom SAMS have strong teaching and research links.

The project will give the student a solid foundation for their thesis with a number of strands of work (Arctic based field work, process study field work, laboratory process studies, analytical analysis) which in turn will provide a comprehensive training in faunal identification, trophic analyses and remote sensing. This PhD project is a part of the larger NERC funded Arctic PRIZE project which is based at SAMS.