Publikationsdatum:
2020-06-20
Beschreibung:
The underside of sea ice in Polar Regions represents a natural habitat for heterotrophic
organisms, such as copepods and amphipods. This under-ice fauna plays a key role in
transferring carbon synthesized by sea ice-associated (sympagic) microalgae into
associated pelagic and benthic food webs of polar ecosystems. Animals at higher trophic
levels are adapted to feed on the under-ice fauna as well as on pelagic zooplankton and
nekton. Polar ecosystems thrive significantly on ice algae-produced carbon depending
on different periods of the year. Thus, the under-ice fauna and the associated pelagic
food web are largely affected by multi-scale climate changes accompanied by the
reduction of sea ice coverage and an increasing duration of the melt season. Until now,
however, the degree to which polar food webs depend on sea ice-derived carbon is
unclear.
The overall aim of this thesis is to quantify the transfer of ice algae-produced carbon
from the sea ice into the under-ice community and from there into pelagic food webs in
Arctic and Antarctic ecosystems, in order to improve our understanding of the potential
ecological consequences of a changing sea ice environment for marine food web
dynamics. Furthermore, spatial and seasonal differences in the utilization of ice algaeproduced
carbon within and between both hemispheres are investigated.
The sample collection in the central Arctic Ocean was carried out during the RV
‘Polarstern’ expedition ARK XXVII-3 (PS80, August-September 2012) within the
Amundsen and Nansen Basins. In the Southern Ocean, samples were collected during the
RV ‘Polarstern’ expeditions ANT XXIX-7 (PS81, August-October 2013) in the northern
Weddell Sea and ANT XXIX-9 (PS82, December 2013-March 2014) offshore from the
Filchner Ice Shelf.
Trophic interactions of important representatives of Arctic and Antarctic food webs are
studied using lipid fingerprinting, stable isotope analysis (SIA) of natural abundance
bulk carbon and nitrogen (BSIA), and compound-specific SIA (CSIA) of fatty acids (FAs).
From the distribution of algae-produced FAs in the consumers (= marker FAs), the
origin of carbon produced by diatoms versus dinoflagellates in key Arctic species
(Chapter I and II) and key Antarctic species (Chapters III-VI) is investigated. Stable
isotope mixing models are used to quantify the relative contribution of bulk carbon and
marker fatty acids derived from ice algae versus pelagic phytoplankton to the carbon
budget of the organisms. Additionally, the stomach contents of polar cod Boreogadus
saida (Chapter II) and Antarctic krill Euphausia superba (Chapter IV) are investigated
to provide information on the most recent diet composition and carbon sources
compared to the long-term trophic signal derived from FA proportions and stable
isotope compositions.
In the Arctic food web, a high contribution of ice algal carbon with up to 90% of the
carbon budget of species with a known strong sea ice association, such as the amphipods
Apherusa glacialis and Onisimus glacialis, is demonstrated. The results also suggest a
substantial ice algae-carbon assimilation by rather pelagic species, such as Calanus
copepods and the pelagic amphipod Themisto libellula during late Arctic summer, in
which sympagic carbon contributed up to 55% of the carbon budget of these species
(Chapter I). Furthermore, a high trophic dependency of polar cod on sea ice-associated
resources is shown (up to 95% ice algal carbon of body carbon), indicating their high
vulnerability in regards to alterations of the sympagic food web (Chapter II).
Chapter III addresses differences in the utilization of ice algal carbon by different
developmental stages of Antarctic krill (Furcilia larvae, juveniles, adults) during late
austral winter. It is shown that young developmental stages thrive significantly on ice
algae produced carbon to survive their first winter, receiving up to two thirds of their
carbon uptake from ice algae. The high spatial and temporal variability in diet and
carbon sources of AC0 krill (larvae, juveniles) across the sampling area in the northern
Weddell Sea is discussed in Chapter IV. Besides young E. superba, the amphipod Eusirus
latircarpus demonstrates a particularly high trophic dependency on sea ice-related
primary production during late austral winter, indicating a proportional contribution of
ice algal carbon of up to 67% of their energy budget. Other important energy linkers
indicate a switch from a predominantly pelagic lifestyle to a strong dependency on ice
algae-produced carbon as the winter season progressed (Chapter V). Among the other
abundant euphausiids collected offshore from the Filchner-Ronne Ice Shelf, Euphausia
crystallorophias and Thysanoessa macrura show that ice algal carbon can serve as
important carbon source during austral summer, accounting for up to 43% of the dietary
carbon in these species (Chapter VI).
In summary, the applied state-of-the art techniques and statistical models allow for a
reliable quantification of the contribution of ice algae-produced carbon to the carbon
budget of ecological key species in both Polar Regions. The results imply that
functioning and carbon dynamics of food webs in both Polar Regions are likely affected
by changes in sea ice coverage and thus ice algal primary production. Due to the close
connectivity between the sea ice ecosystem and the pelagic system, these consequences
will subsequently impact the entire polar ecosystems, their fish populations and
subsequently mammal populations. Moreover, these large amounts of required carbon
for the nutrition of polar food webs, currently fulfilled by ice algae, can likely not be
substituted by an increased pelagic primary production.
Repository-Name:
EPIC Alfred Wegener Institut
Materialart:
Thesis
,
notRev
Format:
application/pdf
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