The role of sympagic meiofauna for the flow of organic matter and energy in the Antarctic and Arctic sea-ice foodwebs

The brine channels in sea ice (Fig. 1) of both polar regions are the habitat of sympagic (ice-associated) bacteria, algae, protozoans and small metazoans > 20 µm (meiofauna, Fig. 2), including copepods, plathyelminthes, rotifers, nematodes, cnidarians, nudibranchs and ctenophores. Primary production of sympagic algae forms the basis of the sea-ice food web, which is coupled to the pelagic ecosystem and higher trophic levels.


Fig. 1: Brine channels make up the habitat of sympagic meiofauna. Brine channels in a chunk of sea ice (left; photo M. Kramer), and resin cast of brine channels (right; photo J. Weissenberger).

The overall objective of this project is to reveal the qualitative and quantitative role of sympagic meiofauna for the flow of organic matter and energy in the Antarctic and Arctic sea-ice foodwebs. The major focus is on sympagic meiofauna because this group could, due to in part very high abundances, play an important role within the sea-ice ecosystem. Moreover, since sympagic metazoans are a food source for higher trophic levels (e.g. larger zooplankton, fish), they probably occupy a key position in coupling processes between the sea ice and pelagic ecosystems. Sympagic meiofauna can thus be supposed to significantly contribute to the flow of organic matter and energy in polar marine food webs. In spite of this, little information on the feeding ecology of this group is available as yet.


Fig. 2: Sympagic meiofauna are metazoans smaller than 20 µm living in the brine channels in sea ice. Harpacticoid copepods (e.g. Tisbe sp., left), nematods (middle) and acoel plathyelminthes (right) are dominant members of the Arctic sympagic meiofauna community (photos: M. Kramer).

Changes in sea-ice cover in the Arctic and possibly parts of the Antarctic may dramatically change the composition of sympagic meiofauna and the timing of ice-algal blooms. Subsequent changes in the food-web structure are likely also to affect higher trophic levels. Therefore, understanding the trophic role of sympagic meiofauna, including diets and ingestion rates, is crucial for predicting the effects of climate change on polar marine ecosystems. The expected results from our project will contribute to this, and to the understanding of the functional ecology of ice-covered ocean ecosystems in general. Furthermore, modifications of existing and establishment of new methods (e. g. preparation of meiofauna for electron microscopic gut content analyses, set-up and evaluation of feeding experiments) will be of interest for studies on benthic meiofauna, as the feeding ecology and role of this group is also poorly understood. The questions addressed are thus of general significance for understanding the functioning of aquatic systems. The investigation has a truly bipolar approach, being based on two expeditions to each Antarctic and Arctic.

The scientific goals will be reached by combining different methodological approaches:

- Morphological / microscopical studies (gut contents)
- Biochemical analyses (fatty acid biomarkers, stable isotopes)
- Feeding experiments (experimental diets and selectivity, ingestion rates)
- Modelling (functional response and competition, grazing and predation impact, conceptual food-web model)

In particular, the following scientific questions are addressed:

- What are the major food sources of the dominant sympagic meiofauna taxa? Based on preliminary results from the pilot phase and first year of the project, we hypothesize that omnivorous and carnivorous feeding and dietary switches are more widespread amongst sympagic meiofauna than commonly assumed (Fig. 3). The methods applied to address this question are feeding experiments with algae, ciliates and metazoans as food (including food-choice experiments), analyses of in situ gut contents and the use of fatty acid biomarkers and stable isotopes, in combination with the application of mathematical models.

- What are the ingestion rates of the dominant sympagic meiofauna taxa, and what is the functional relationship to density of food and grazers / predators? The hypotheses, partly based on observations during the pilot phase and first year of the project, are: (i) Ingestion rates of sympagic meiofauna can, as an adaptation to variable food availability in the sea-ice habitat, strongly fluctuate with time and, under certain conditions, reach high values. (ii) Ingestion rates can increase with food density (the commonly observed functional response) and decrease with predator density (as an effect of competition); both effects may be particularly related to the sympagic life style. The objectives are, for each meiofauna taxon studied, to express the ingestion rate as a function of predator and prey density and to quantify the specific amount of food and energy required. The methods used in this approach will be measurements of grazing and predation rates in feeding experiments with algae, ciliates and metazoans as food, combined with modelling.

- What is the grazing and predation impact of sympagic meiofauna on the standing stocks of sympagic ice algae, protozoans and metazoans with different community compositions? The hypotheses behind this question are: (i) The impact of sympagic meiofauna on their food sources inside the ice is more diverse than commonly assumed. (ii) The impact is quantitatively higher than suggested by theoretical calculations based on allometric functions, which have been developed for fundamentally different organisms (zooplankton) and feeding types (filter feeders). This impact will be calculated by a combination of ingestion rates and abundance and biomass data.

- How does the trophic structure of the sympagic food web (particularly grazing and predation by sympagic meiofauna) influence the abundances and short-term dynamics of the sympagic community? We hypothesise that feeding activity of sympagic meiofauna can under certain conditions significantly influence the abundances of sympagic organisms and, hence, the population dynamics of the sympagic ecosystem. To address this question, we will construct a conceptual food-web model for the sympagic community, which will include meiofauna as a central part, and which will be based on the qualitative and quantitative trophic relationships determined in the course of the project.


Fig. 3: The sympagic food web is commonly assumed to have a simple structure, with sympagic meiofauna feeding preliminarily on sympagic algae (upper panel). We hypothesize the food-web structure to be more complex; carnivorous feeding on ciliates may play a substantial role in the sea-ice food web (lower panel).

Scientists

Iris Werner
Institute for Polar Ecology
University of Kiel

Michael Spindler
Institute for Polar Ecology
University of Kiel

Maike Kramer
Institute for Polar Ecology
University of Kiel

Rainer Kiko
Institute for Polar Ecology
University of Kiel

Miriam Marquardt
Institute for Polar Ecology
University of Kiel

Research areas

Western Weddell Sea (Antarctic)
East Antarctic
Central and Siberian Arctic
Western Canadian Arctic

Publications

Marquardt M, Kramer M, Werner I, Carnat G, (accepted). Vertical distribution of sympagic meiofauna in sea ice in the Canadian Beaufort Sea. Polar Biology.

Kiko R, Kern S, Kramer M, Mütze H, (submitted). Colonization of newly forming Arctic sea ice by meiofauna - a case study for the future Arctic? Marine Ecology Progress Series.

Kramer M, Struck U, Schukat A, Kiko R, Werner I, (submitted). Trophic positions of Arctic and Antarctic sympagic meiofauna and its role in cryo-pelagic coupling identified by stable isotopes and fatty acids. Marine Ecology Progress Series.

Kramer M, Swadling KM, Meiners KM, Kiko R, Scheltz A, Nicolaus M, Werner I, 2011. Antarctic sympagic meiofauna in winter: comparing diversity, abundance and biomass between perennially and seasonally ice-covered regions. Deep-Sea Research II 58, 1062–1074.

Kramer M, Kiko R, 2011. Brackish meltponds on Arctic sea ice—a new habitat for marine metazoans. Polar Biology 34, 603–608.

Siebert S, Anton-Erxleben F, Kiko R, Kramer M, 2009. Sympagohydra tuuli—first report from sea ice of the central Arctic Ocean and insights into histology, reproduction and locomotion. Marine Biology 156, 541–554.

Kiko R, Kramer M, Spindler M, Wägele H, 2008. Tergipes antarcticus (Gastropoda, Nudibranchia): distribution, life cycle, morphology, anatomy and adaptation of the first mollusc known to live in Antarctic sea ice. Polar Biology 31, 1383–1395.

Kramer M, 2010. The role of sympagic meiofauna in Arctic and Antarctic sea-ice food webs. Doctoral thesis, Institute for Polar Ecology, University of Kiel.

Marquardt M, 2010. Studies on sympagic meiofauna in fast and pack ice in the southeastern Beaufort Sea (Canadian Arctic). Diploma thesis, Institute for Polar Ecology, University of Kiel.

Homepage

http://www.uni-kiel.de/ipoe

Research funding organisation

Deutsche Forschungsgemeinschaft (German Research Foundation, DFG)

Project number: WE 2536 / 11-1
Funding period: October 2007 – October 2009