The role of sympagic meiofauna for the flow of organic matter and energy in the Antarctic and Arctic sea-ice foodwebs
Zusammenfassung der Projektergebnisse
We combined meiofauna community studies, biochemical analyses and feeding experiments to test our hypotheses that (1) due to carnivorous, cilivorous and omnivorous sympagic meiofauna, the sea-ice food webs are more complex than previously assumed, (2) ingestion rates of sympagic meiofauna are highly variable and depend on meiofauna and food density, (3) the feeding impact of sympagic meiofauna is more diverse and may have been underestimated, (4) sympagic meiofauna plays an important role in cryo-pelagic coupling, and (5) global warming may affect Arctic sympagic meiofauna composition and feeding strategies, with possible consequences for the entire Arctic marine food web. Sea-ice samples were taken in the Antarctic (western Weddell Sea and southern Indian Ocean, in winter) and in the Arctic (Central Arctic, in summer; Canadian Arctic and Spitsbergen fjords, in spring). Additionally, brackish meltponds on summer sea ice in the Central Arctic were sampled. Antarctic sympagic meiofauna comprised, besides the commonly reported taxa, also the ctenophore Euplokamis sp., the nudibranch Tergipes antarcticus, cyclopoid copepods and rhabdocoel platyhelminthes. Diversity, abundance and biomass of metazoan meiofauna were significantly higher in the perennially ice-covered western Weddell Sea than in the seasonally ice-covered southern Indian Ocean. Arctic sympagic meiofauna likewise included taxa new to sea ice: the cnidarian Sympagohydra tuuli, the calanoid copepod Eurytemora richingsi, nemerteans and white-rose acoel platyhelminthes. Brackish meltponds hosted various proto- and metazoans in new ice covering the pond surfaces as well as in and on the very porous ice at the pond bottoms. Stable isotope and fatty acid analyses served to gain information on in situ feeding of sympagic meiofauna. We developed a two-source model to estimate trophic positions and to identify feeding grounds based on stable isotopes. In order to identify diets, to determine ingestion rates and to assess selectivity, we conducted grazing and predation experiments with various Arctic and Antarctic sympagic meiofauna taxa, for which we specifically developed new methods and modified established ones. The biochemical analyses and feeding experiments showed in good agreement that most metazoan meiofauna taxa prey on ciliates. Some taxa even prey on metazoans. Many of these taxa are omnivores which supplement their diets with algae, bacteria and detritus. A few meiofauna taxa are mainly herbivorous, but can additionally prey on ciliates, or cannibalistically feed on their nauplii. Ingestion rates were influenced by food density (functional response) and predator density (competition). Grazing rates of Tisbe spp. were generally lower than theoretically derived maximum potential ingestion rates (I max). The experimentally derived grazing impact of the meiofauna community was by one order of magnitude lower than estimates from Imax. Predation rates, in contrast, were very high in some metazoan meiofauna taxa, in part exceeding Imax. The experimentally derived predation impact of the meiofauna community was accordingly high. We draw the following conclusions: As hypothesized, (1) sea-ice food webs are more complex than previously assumed and (2) ingestion rates are highly variably and can be influenced by meiofauna and food density. (3) The results confirm a diverse feeding impact of sympagic meiofauna on algae, ciliates and metazoan meiofauna. The hypothesis of a high feeding impact is confirmed for predation on ciliates and copepods, but not for grazing on algae. Predation by meiofauna may change the meiofauna community structure. (4) Cryo-pelagic coupling is influenced by meiofauna predation, which can diminish the amount of meiofauna released from the ice and available to under-ice and sub-ice predators. New pathways in cryo-pelagic coupling are feeding migrations of meiofauna between the sea ice, meltponds and the pelagic realm, which can enhance interactions with under-ice and sub-ice fauna. (5) The gradual loss of perennial sea ice in the Arctic in consequence of global warming probably causes a decrease in sympagic meiofauna diversity, abundance and biomass. Consequently, the sea-ice food web may become less complex and more vulnerable. Under-ice and sub-ice predators may be affected by the shift in potential prey taxa. Over the next decades, an increase in brackish meltponds might locally enhance cryo-pelagic coupling in late summer. The expected long-term changes in the quantity and quality of cryo-pelagic coupling deserve further investigation.
Projektbezogene Publikationen (Auswahl)
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(2008) Sea ice biology. In: Schauer U (Ed) The expedition ARKTIS-XXII/2 of the Research Vessel „Polarstern“ in 2007. Ber Polarf Meeresf 579:65–75
Kiko R, Kramer M, Siebert S, Schneider A, Bakker K, Kuckero L
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(2008) Tergipes antarcticus (Gastropoda, Nudibranchia): distribution, life cycle, morphology, anatomy and adaptation of the first mollusc known to live in Antarctic sea ice. Polar Biol 31:1383–1395
Kiko R, Kramer M, Spindler M, Wägele H
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(2009) Life cycle strategy of pelagic and sympagic zooplankton. In: Lemke P (Ed) The expedition of the Research Vessel „Polarstern“ to the Antarctic in 2006 (ANT-XXIII/7). Ber Polarf Meeresf 586:102–112
Cornils A, Kiko R, Kramer M, Nachtigal K, Norman L, Papadimitriou S, Sartoris FJ, Schiel S, Stefels J, Thomas D
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(2009) Meiofauna. In: Barber DG, Papakyriakou T (Ed) Circumpolar Flaw Lead System Study (CFL) – scientific cruise reports compendium: Leg 7, 406–408
Lacoste C, Kramer M
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(2009) Meiofauna. In: Gosselin M, Tremblay J-E, Barber DG (Ed) Circumpolar Flaw Lead System Study (CFL) – scientific cruise reports compendium: Leg 8, 541–545
Nozais C, Lacoste C, Kramer M, Scheltz A
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(2009) Sympagohydra tuuli—first report from sea ice of the central Arctic Ocean and insights into histology, reproduction and locomotion. Marine Biol 156:541–554
Siebert S, Anton-Erxleben F, Kiko R, Kramer M
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(2010) The role of sympagic meiofauna in Arctic and Antarctic sea-ice food webs. Doctoral thesis, Institute for Polar Ecology, University of Kiel
Kramer M
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(2011) Antarctic sympagic meiofauna in winter: comparing diversity, abundance and biomass between perennially and seasonally ice-covered regions. Deep-Sea Res II 58:1062–1074
Kramer M, Swadling KM, Meiners KM, Kiko R, Scheltz A, Nicolaus M, Werner I
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(2011) Brackish meltponds on Arctic sea ice - a new habitat for marine metazoans. Polar Biol 34:603–608
Kramer M, Kiko R
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(2011) Vertical distribution of sympagic meiofauna in sea ice in the Canadian Beaufort Sea. Polar Biol
Marquardt M, Kramer M, Werner I, Carnat G
