The influence of light and nutrients on buoyancy, filament aggregation and flotation of Anabaena circinalis |
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| Authors: | Brookes J; Ganf G; Green D; Whittington J |
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| Institution: | Botany Department, The University of Adelaide, North Tce., Adelaide, South Australia, 5005; CRC for Freshwater Ecology, Murray Darling Freshwater Research Centre, PO Box 921, Albury, NSW, 2640, Australia; Present address: CRC for Water Quality and Treatment, Private Mail Bag 3, Salisbury, South Australia, 5108, Australia |
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| Abstract: | At Chaffey Dam, New South Wales, Australia, Anabaena
circinalis filaments accumulated at the surface as diurnal
surface layer thermal stratification developed. Previously buoyant,
homogeneously distributed colonies accumulated in the top 2 m, but a
proportion lost buoyancy. Similarly, a percentage of
A.circinalis suspended in bottles lost buoyancy at
depths experiencing >30% surface irradiance
(Io). Nutrient addition reduced the proportion of
filaments that lost buoyancy following a full day of high irradiance. The
greatest axial linear dimension (GALD) was measured for
A.circinalis deployed in bottles at three depths in
the reservoir. GALD increased in samples exposed to 1 and 30%
Io by the following day. The rank order of GALD from
smallest to largest grouped samples exposed to 70, 30 and 1%
Io, suggesting that increasing GALD is a function of
irradiance. The increased GALD of biomass units was attributed to
aggregation of filaments in low light. The enlargement of biomass units
increased the mean floating velocity, supporting the theory that filament
aggregation may be a strategy, utilized by light-limited filaments, to
increase light exposure. High irradiance increased the carbohydrate content
of cells and decreased the floating velocity of filaments.
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