Rolf Gradinger

REGIONAL VARIABILITY IN FOOD AVAILABILITY FOR ARCTIC MARINE MAMMALS

This review provides an overview of prey preferences of seven core Arctic marine mammal species (AMM) and four non-core species on a pan-Arctic scale with regional examples. Arctic marine mammal species exploit prey resources close to the sea ice, in the water column, and at the sea floor, including lipid-rich pelagic and benthic crustaceans and pelagic and ice-associated schooling fishes such as capelin and Arctic cod. Prey preferred by individual species range from cephalopods and benthic bivalves to Greenland halibut. A few AMM are very prey-, habitat-, and/or depth-specific (e.g., walrus, polar bear), while others are rather opportunistic and, therefore, likely less vulnerable to change (e.g., beluga, bearded seal). In the second section, we review prey distribution patterns and current biomass hotspots in the three major physical realms (sea ice, water column, and seafloor), highlighting relations to environmental parameters such as advection patterns and the sea ice regime. The third part of the contribution presents examples of documented changes in AMM prey distribution and biomass and, subsequently, suggests three potential scenarios of large-scale biotic change, based on published observations and predictions of environmental change. These scenarios discuss (1) increased pelagic primary and, hence, secondary production, particularly in the central Arctic, during open-water conditions in the summer (based on surplus nutrients currently unutilized); (2) reduced benthic and pelagic biomass in coastal/shelf areas (due to increased river runoff and, hence, changed salinity and turbidity conditions); and (3) increased pelagic grazing and recycling in open-water conditions at the expense of the current tight benthic-pelagic coupling in part of the ice-covered shelf regions (due to increased pelagic consumption vs. vertical flux). Should those scenarios hold true, pelagic-feeding and generalist AMM might be advantaged, while the range for benthic shelf-feeding, ice-dependent AMM such as walrus would decrease. New pelagic feeding grounds may open up to AMM and subarctic marine mammal species in the High Arctic basins while nearshore waters might provide less abundant food in the future.

Implications of brine channel geometry and surface area for the interaction of sympagic organisms in Arctic sea ice

Dynamic temporal and spatial changes of physical, chemical and spatial properties of sea ice pose many challenges to the sympagic community which inhabit a network of brine channels in its interior. Experiments were conducted to reveal the influence of the internal surface area and the structure of the network on species composition and distribution within sea ice. The surface of the brine channel walls was measured via a newly developed method using a fluorogenic tracer. These measurements allowed us to quantify the internal surface area accessible for predators of different sizes, at different ice temperatures and in different ice textures. Total internal surface area ranged from 0.6 to 4 m2 kg−1 ice and declined with decreasing ice temperature. Potentially, 6 to 41% of the area at −2°C is covered by micro-organisms. Cooling from −2 to −6°C drastically increases the coverage of organisms in brine channels due to a surface reduction. A combination of brine channel frequency measurements with an artificial brine network experiment suggests that brine channels ≤200 μm comprise a spatial refuge with microbial community concentrations one to two magnitudes higher than in the remaining channel network. The plasticity of predators to traverse narrow passages was experimentally tested for representative Arctic sympagic rotifers, turbellarians, and nematodes. By conforming to the osmotic pressure of the brine turbellaria match their body dimensions to the fluctuating dimensions of the brine channel system during freezing. Rotifers penetrate very narrow passages several times their body length and 57% their body diameter. In summary, ice texture, temperature, and bulk salinity influence the predatory–prey interactions by superimposing its structural component on the dynamic of the sympagic food web. Larger predators are excluded from brine channels depending on the architecture of the channel network. However, extreme body flexibility allows some predators to traverse structural impasses in the brine channel network.

Biological Response to Recent Pacific Arctic Sea Ice Retreats

Although recent major changes in the physical domain of the Arctic region, such as extreme retreats of summer sea ice since 2007, are well documented, large uncertainties remain regarding responses in the biological domain. In the Pacific Arctic north of Bering Strait, reduction in sea ice extent has been seasonally asymmetric, with minimal changes until the end of June and delayed sea ice formation in late autumn. The effect of extreme ice retreats and seasonal asymmetry in sea ice loss on primary production is uncertain, with no clear shift over time (2003–2008) in satellite-derived chlorophyll concentrations. However, clear changes have occurred during summer in species ranges for zooplankton, bottom-dwelling organisms (benthos), and fish, as well as through the loss of sea ice as habitat and platform for marine mammals.

Food web structure in the high Arctic Canada Basin: evidence from δ13C and δ15N analysis

The food-web structure of the Arctic deep Canada Basin was investigated in summer 2002 using carbon and nitrogen stable isotope tracers. Overall food-web length of the range of organisms sampled occupied four trophic levels, based on 3.8‰ trophic level enrichment (δ15N range: 5.3–17.7‰). It was, thus, 0.5–1 trophic levels longer than food webs in both Arctic shelf and temperate deep-sea systems. The food sources, pelagic particulate organic matter (POM) (δ13C=−25.8‰, δ15N=5.3‰) and ice POM (δ13C=−26.9‰, δ15N=4.1‰), were not significantly different. Organisms of all habitats, ice-associated, pelagic and benthic, covered a large range of δ15N values. In general, ice-associated crustaceans (δ15N range 4.6–12.4‰, mean 6.9‰) and pelagic species (δ15N range 5.9–16.5, mean 11.5‰) were depleted relative to benthic invertebrates (δ15N range 4.6–17.7‰, mean 13.2‰). The predominantly herbivorous and predatory sympagic and pelagic species constitute a shorter food chain that is based on fresh material produced in the water column. Many benthic invertebrates were deposit feeders, relying on largely refractory material. However, sufficient fresh phytodetritus appeared to arrive at the seafloor to support some benthic suspension and surface deposit feeders on a low trophic level (e.g., crinoids, cumaceans). The enriched signatures of benthic deposit feeders and predators may be a consequence of low primary production in the high Arctic and the subsequent high degree of reworking of organic material.

Controls of the landfast ice-ocean ecosystem offshore Barrow, Alaska

Abstract Based on biophysical ice-core data collected in the landfast ice off Barrow, Alaska, USA, in 2002 and 2003, a one-dimensional ice–ocean ecosystem model was developed to determine the factors controlling the bottom-ice algal community. The data and model results revealed a three-stage ice-algal bloom: (1) onset and early slow growth stage before mid-March, when growth is limited by light; (2) fast growth stage with increased light and sufficient nutrients; and (3) decline stage after late May as ice algae are flushed out of the ice bottom. Stages 2 and 3 are either separated by a transition period as in 2002 or directly connected by ice melting as in 2003, when in situ light and nutrient enrichment experiments showed only light limitations. The modeled net primary production of ice algae (NPPAi) from March to June is 1.2 and 1.7 g Cm–2 for 2002 and 2003, respectively, within the range of previous observations. Model sensitivity studies found that overall NPPAi increased almost proportionally to the initial nutrient concentrations in the water column. A phytoplankton bloom (if it occurs as in 2002) would compete with ice algae for nutrients and lead to reduced NPPAi. About 45% of the NPPAi was exported to the shallow benthos.

Distribution of phytoplankton communities in relation to the large-scale hydrographical regime in the Fram Strait

In June and July 1984 phytoplankton distribution was investigated in the Fram Strait between Greenland and Svalbard. Chlorophylla, particulate organic carbon, nitrate and phytoplankton species composition were determined from six different depths in the upper 200 m of the water column. Multivariate analysis methods were applied to identify phytoplankton communities in relation to different hydrographic regimes. Three main domains could be distinguished in terms of both hydrography and biology: (1) the East Greenland shelf polynya with a high biomass mainly produced by chain-forming diatoms, (2) the ice-covered East Greenland Current with an extremely low standing stock dominated by flagellates and (3) the marginal ice zone with a biomass maximum in 20 to 40 m depth formed by diatoms, dinoflagellates andPhaeocystis pouchetii.

Flagellates and heliozoans in the Greenland Sea ice studied alive using light microscopy

Abstract The occurrence of flagellates and heliozoans in the Greenland Sea was determined from freshly collected samples and crude cultures established during the expedition ARK XI/2 onboard RV “Polarstern” in autumn 1995. The live material was collected from the water column, new ice, and multi-year ice floes, and examined with light (interference and phase contrast) and epifluorescence microscopy. Photographic and video techniques were utilised for the documentation. The observed general morphology of the cells, swimming motions, feeding behaviour and modes of reproduction assisted in the identification of flagellates. A total of 57 photo- and heterotrophic flagellate taxa, representing cryptophytes, dinoflagellates, haptophytes, chrysophytes, Prasinophyceae, chlorophytes, euglenids, choanoflagellates, kinetoplastids, protists of unknown affinity (Protista incertae sedis), and heliozoans, were found. Diatoms were excluded from this study. Newly forming ice, ice floes and cultures established from the ice samples contained almost twice as many identified flagellate taxa as the water column. In addition to general information on the community structure of flagellates and heliozoans, the light microscopical methods used here provided information on the need for additional microscopy, establishment of cultures, and the suitability of the material for experimental work.

The Biology of Polar Regions

Preface 1. Introduction to the Polar Regions 2. Stress, Adaptation and Survival in Polar Regions 3. Periglacial and Terrestrial Habitats in Polar Regions 4. Glacial Habitats in Polar Regions 5. Inland Waters in Polar Regions 6. Open Oceans in Polar Regions 7. Frozen Oceans in Polar Regions 8. Marine Benthos in Polar Regions 9. Birds and Mammals in Polar Regions 10. Climate Change in Polar Regions 11. Human impacts on Polar Regions 12. Some Conclusions Further Reading & Web Resources References Index

Climate Change and Biological Oceanography of the Arctic Ocean

Polar environments are characterized by unique physical and chemical conditions for the development of life. Low temperatures and the seasonality of light create one of the most extreme habitats on Earth. The Arctic sea ice cover not only acts as an insulator for heat and energy exchange processes between ocean and atmosphere but also serves as a unique habitat for a specialized community of organisms, consisting of bacteria, algae, protozoa and metazoa. The primary production of sea ice algae may play a crucial role in the life cycle of planktonic and benthic organisms. Thus, a reduction of the sea ice extent due to environmental changes will influence the structure and processes of communities living inside the ice and pelagic realms.

Integrated abundance and biomass of sympagic meiofauna in Arctic and Antarctic pack ice

Abstract The abundance and biomass of sympagic meiofauna were studied during three cruises to the Antarctic and one summer expedition to the central Arctic Ocean. Ice samples were collected by ice coring and algal pigment concentrations and meiofauna abundances were determined for entire cores. Median meiofauna abundances for the expeditions ranged from 4.4 to 139.5 × 103 organisms m−2 in Antarctic sea ice and accounted for 40.6 × 103 organisms m−2 in Arctic multi-year sea ice. While most taxa (ciliates, foraminifers, turbellarians, crustaceans) were common in both Arctic and Antarctic sea ice, nematodes and rotifers occurred only in the Arctic. Based on the calculated biomass, the potential meiofauna ingestion rates were determined by applying an allometric model. For both hemispheres, daily and yearly potential ingestion rates were below the production values of the ice algal communities, pointing towards non-limited feeding conditions for ice meiofauna year-round.