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Planktonic interactions and particulate flux in Ellis Fjord, east Antarctica


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Beaumont, KL 2003 , 'Planktonic interactions and particulate flux in Ellis Fjord, east Antarctica', PhD thesis, University of Tasmania.

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The Southern Ocean is one of the largest marine ecosystems in the world,
and is a major sink for atmospheric carbon dioxide. Thus, it plays a
considerable role in the mitigation of the greenhouse effect and resultant
global warming. Marine micro-organisms dominate the plankton biomass in
Antarctic waters, consume much of the primary production, and are
principal determinants of the transfer and vertical flux of photosyntheticallyfixed
carbon. This thesis examines the composition and trophodynamics of a
plankton community dominated by microzooplankton grazers, and their
role in vertical carbon flux in an east Antarctic fjord. Ellis Fjord is a semiisolated
marine inlet that is usually ice-covered throughout the year, and
supports a zooplankton community that has low species richness and is
dominated by microzooplankton. As such, it is akin to a macrocosm in
which the role of microzooplankton in carbon dynamics can be studied in
detail, in the relative absence of strong hydrodynamic forcing and the
influence of higher trophic levels.
The seasonal succession of the plankton community in Ellis Fjord was
similar to that commonly observed in the wider Southern Ocean; changing
from dominance by microplanktonic diatoms and small herbivorous
copepods during early summer to nanoflagellates and protozoa during late
summer. MicroplanIctonic diatom blooms and herbivorous grazers are
commonly regarded as contributing to carbon export in the Southern Ocean,
while communities dominated by auto- and heterotrophic nanoplankton
favour the retention and respiration of carbon in pelagic waters. In Ellis
Fjord, the physiological state of the cells appeared to determine their
buoyancy, as microplanktonic diatoms did not directly sediment until the
bloom declined. While there was evidence of near-surface export of
microplanktonic diatoms, heterotrophic nanoflagellates, and
microzooplankton faecal pellets, these contributed little to vertical flux to
depth. Grazing by microzooplanIcton retarded the flux of phytoplankton by
reducing the number of cells available to sediment directly, by producing
faecal pellets of a morphology and ultrastructure that inhibited sinking, and
by coprophagous degradation and recycling of pellets.
Most pellets at depth were minipellets that contained little carbon, many of
which appeared to be 'false' minipellets caused by coprophagy and
degradation. Surprisingly, protozoan pellets that contained only empty
diatom frustules contained more carbon per pellet than small oval copepod
pellets. Differences in the ecology of the dominant small copepods, Oithona
similis and Oncaea curvata, affected the morphology, persistence, and carbon
content of their pellets, and the distribution of their biomass in the water
column. Despite differences within and between small copepod and
protozoan taxa, models of carbon flux in Ellis Fjord indicate that these
microzooplankton contribute to the retention of both new and regenerated
production. This reduces the draw-down of atmospheric carbon in Antarctic
waters and the capacity of these waters to ameliorate global climate change.

Item Type: Thesis - PhD
Authors/Creators:Beaumont, KL
Keywords: Plankton, Plankton populations
Copyright Holders: The Author
Copyright Information:

Copyright 2003 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Chapter 4 published in part as Beaumont KL, Nash GV, Davidson AT (2002) Ultrastructure, morphology and flux of microzooplankton faecal pellets in an east Antarctic fjord. Marine Ecology Progress Series 245:133-148.

Includes notes in back pocket. Thesis (Ph.D.)--University of Tasmania, 2003. Includes bibliographical references

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