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Surviving under the Antarctic sea ice : a study of the feeding ecology of Antarctic krill

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Jia, Z (2016) Surviving under the Antarctic sea ice : a study of the feeding ecology of Antarctic krill. PhD thesis, University of Tasmania.

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Abstract

Antarctic sea ice covers approximately 4 million km2 during minimum extent in February/
March and grows to 19 million km2 during maximum extent in September/October.
This sea ice zone harbours a wide diversity of biota and supports large populations
of unique Antarctic organisms. During the satellite era, Antarctic sea ice has shown
strong regional changes in its extent, duration, and the timing of the annual advance
and retreat. Improving our understanding of the relationships between sea ice and ice associated
animals will fill a crucial knowledge gap, which will facilitate the conservation
and management of the Southern Ocean ecosystems and resources.
This thesis compiles three studies focusing on the feeding ecology of Antarctic ice associated
zooplankton during the winter-spring transition. This work concentrates
on Antarctic krill (Euphausia superba), a key species with ecological and commercial
significance in Southern Ocean ecosystems.
Morphology defines an animal’s feeding capability. The morphological changes through
ontogeny of a species thus are not only important taxonomic information, but also crucial
for our understanding regarding its feeding ecology. In Chapter 2, I describe the
morphological changes of E. superba through its development from an egg to juvenile.
This is the first study since 1936 that fully describes the morphological features of
this species, in which I update the existent knowledge with details and high-resolution
photographs. Intermediate larval stages are identified and these morphological characteristics
are related to the overwintering survival strategies for this species.
The food that animals actually obtain from the environment can be investigated with
either gut content or biochemical analyses. To determine the dietary preferences and
trophic relationships of major zooplankton species (Chapter 3), I use stable isotope analyses
(13C/12C and 15N/14N) to compare samples collected from East Antarctic pack ice
zone during two winter-spring transitions (2007 and 2012). Interannual dietary differences
are determined for larval E. superba, suggesting feeding plasticity, which enables
this species to adapt to changing environmental conditions. Larval E. superba are primarily
herbivorous while utilising sea-ice biota, and consume a more heterotrophic diet
when feeding from the water column. In contrast, post-larval E. superba, and the omnivorous
krill Thysanoessa macrura consume a mixed diet from both the water column and
the sea ice. The pteropod Limacina helicina, small copepods in the genus Oithona spp.,
ostracods and amphipods rely heavily on sea-ice biota according to their carbon isotope
ratios. Large copepods and chaetognaths consume a water column-based diet during the
winter. The comparison of isotopic profiles between years suggests that ice-associated
zooplankton gain access to sea-ice biota more easily under warm and permeable ice than
under cold ice.
Our ability to construct food web models for sea-ice ecosystems are restricted by limited
real data and inadequate understanding regarding the system structure. A qualitative
modelling approach is applied in Chapter 4 to explore how the increasing model complexity
affects model predictions, and to identify key variables and interactions governing
krill dynamics in this system. A series of qualitative network models are constructed
to represent different theories of krill winter feeding, and winter conditions are simulated
by applying a perturbation of an increase in sea-ice algae and a decrease in
pelagic phytoplankton concurrently. Results demonstrate the importance of including
developmental-stage-specific information during the construction of food web models. In
addition, model outcomes suggest that the coupling between primary production (either
sea-ice or pelagic) and protozoan production should be investigated in future empirical
studies as it is a key process affecting model predicted krill responses. This study
also demonstrates the usefulness of qualitative network modelling in hypotheses testing
regarding ecological processes.
This thesis has contributed to a better understanding of feeding ecology of Antarctic
krill and other under-ice zooplankton during the winter-spring transition period. My results
suggest that future studies regarding feeding ecology of ice-associated zooplankton
should use combined approaches. The use of qualitative modelling could help evaluate
assumptions based on limited data, which is advantageous for identifying critical
ecological processes and pinpointing the empirical observations that are needed. In addition,
advanced technologies, such as high-resolution underwater camera and underwater
vehicles, will allow us to obtain habitat-structure information and detailed in situ behavioural
observations, which should also be evaluated and considered in future feeding
studies.

Item Type: Thesis (PhD)
Keywords: Antarctic krill, sea ice, zooplankton ecology, stable isotope, food web modelling
Copyright Information:

Copyright 2016 the Author

Additional Information:

Chapter 2 appears to be the equivalent of a post print version of an article published as: Jia, Z., Virtue, P., Swadling, K.M.,
Kawaguchi, S. (2014) A photographic documentation of the development of Antarctic krill (Euphausia superba) from egg to early juvenile. Polar biology 37(2), 165-179. The final publication is available at Springer via http://dx.doi.org/10.1007/s00300-013-1420-7

Chapter 3 appears to be the equivalent of a post print version of an article published as: Jia, Z., Swadling, K.M., Meiners, K.M., Kawaguchi, S., Virtue, P. (2016) The zooplankton food web under East Antarctic pack ice - a stable isotope study. Deep sea research part II: topical studies in oceanography 131, 189-202.

Date Deposited: 30 Oct 2016 21:58
Last Modified: 09 Nov 2016 23:25
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