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Ecophysiology and competitive ability of Anabaena circinalis, a bloom-forming cyanobacterium


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McCausland, Malcolm Andrew 2003 , 'Ecophysiology and competitive ability of Anabaena circinalis, a bloom-forming cyanobacterium', PhD thesis, University of Tasmania.

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Blooms of the toxic cyanobacterium A. circinalis are a major problem in Australia.
Further knowledge of this species and its competitors is of great importance to
understand how the incidence of such blooms may be reduced. Experiments
undertaken at a range of scales, from culture tubes to lm high microcosms
examined the role of (1) light and mixing, (2) nitrogen type and availability and (3)
pH and carbon availability in the dynamics of A. circinalis and its competitors - the
diatom Aulacoseira sp. and the cyanobacterium Microcystis aeruginosa. In single
species (A. circinalis, Aulacoseira sp.) microcosm experiments with vertically
attenuated light environments, the growth of A. circinalis was significantly higher at
48 h mixing intervals than at 10 min intervals at the highest vertical light attenuation tested (k(0.3 = 9.7, Zm :Zeu= 6.25). The difference in growth was due to a
combination of light availability and the physiological responses to it (i.e. increased
buoyancy). This enabled A. circinalis greater access to light at the longer mixing
interval. The contrary was true of Aulacoseira sp. which had significantly slower
growth in all light environments at 48 h mixing intervals relative to 10 min
intervals. Aulacoseira sp. had lowered access to light due to its high sinking rate.
In competition experiments, A. circinalis dominated over Aulacoseira sp. at 48 h
and 96 h mixing intervals, however both species co-existed at 10 min intervals. In
combined species microcosm experiments (A. circinalis, Aulacoseira sp.,
Microcystis aeruginosa), there was no difference in species composition when N
was supplied as nitrate or ammonium. Where no DIN was supplied, A. circinalis
quickly gained dominance. An initial reduction in growth in the non-N2-fixing species (Aulacoseira sp., M. aeruginosa), was followed by a substantial increase.
The results suggest the increase in growth was indirectly supported by N leaked into
the medium by A. circinalis. In sealed culture experiments, growth rates of A.
circinalis did not differ across a broad pH range (7.5 to 9.1). In comparison
Aulacoseira sp. had significantly lower growth at high pH (9.0-9.1) relative to low
pH (7.5-7.7). Evidence from δ13C measurements strongly suggests that both species
utilise bicarbonate at high pH, however the difference in growth rate suggests that
Aulacoseira sp. is less efficient in utilising carbon via this pathway. All results are
discussed in the context of the Australian environment. It is concluded that mixing
and light, nitrogen and carbon availability are all potentially significant factors in
the formation and/or maintenance of A. circinalis blooms.

Item Type: Thesis - PhD
Authors/Creators:McCausland, Malcolm Andrew
Keywords: Algal blooms, Cyanobacteria, Algae
Copyright Holders: The Author
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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
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Thesis (PhD.)--University of Tasmania, 2003. Includes bibliographical references

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