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Behavioural patterns and growth strategies of red tide organisms of the southern Benguela
Author(s)
Horstman, Deon A
Date Issued
1996
Type
Thesis
Publisher
Cape Technikon
Abstract
Red tides are a common feature of the southern Benguela upwelling system and are usually
dominated by migratory flagellates and the ciliate Mesodinium rubrum. Seasonal blooms of
dinoflagellates occur in response to seasonal upwelling and typically succeed diatom blooms.
High biomass, multispecies red tides result from concentration by various physical forces and
are characteristically found in warm, stratified, nutrient-depleted water overlying cold,
nutrient-rich bottom water. The influence of turbulent mixing, light and the availability of
nutrients on the migratory behaviour of red tide species was studied by means of both
mesocosm and field studies. The mesocosm experiments were conducted in a 3m laboratory
column in which a red tide community, collected from the field, was introduced above
nutrient-rich bottom water. All the dominant species exhibited directed vertical migration,
with ascent and descent starting before sunrise and before sunset respectively. Observations
support the hypothesis that red tide organisms can sustain high concentrations in nitrogen
depleted surface waters by growing at the expense of nitrate taken up during nocturnal
descent. Vertical niche separation of different red tide species was evident both during the
night and the day. Observations support the hypothesis that species are capable of coexisting
within a red tide bloom. Division rates were determined from the frequency of paired nuclei
and cells. C. furca recorded the highest growth rate (u = 0.24). The relatively low growth
rates emphasise the importance of physical processes, as opposed to biological processes, in
the formation of red tides within upwelling systems.
dominated by migratory flagellates and the ciliate Mesodinium rubrum. Seasonal blooms of
dinoflagellates occur in response to seasonal upwelling and typically succeed diatom blooms.
High biomass, multispecies red tides result from concentration by various physical forces and
are characteristically found in warm, stratified, nutrient-depleted water overlying cold,
nutrient-rich bottom water. The influence of turbulent mixing, light and the availability of
nutrients on the migratory behaviour of red tide species was studied by means of both
mesocosm and field studies. The mesocosm experiments were conducted in a 3m laboratory
column in which a red tide community, collected from the field, was introduced above
nutrient-rich bottom water. All the dominant species exhibited directed vertical migration,
with ascent and descent starting before sunrise and before sunset respectively. Observations
support the hypothesis that red tide organisms can sustain high concentrations in nitrogen
depleted surface waters by growing at the expense of nitrate taken up during nocturnal
descent. Vertical niche separation of different red tide species was evident both during the
night and the day. Observations support the hypothesis that species are capable of coexisting
within a red tide bloom. Division rates were determined from the frequency of paired nuclei
and cells. C. furca recorded the highest growth rate (u = 0.24). The relatively low growth
rates emphasise the importance of physical processes, as opposed to biological processes, in
the formation of red tides within upwelling systems.
Additional information
Thesis (Master in Technology)--Cape Technikon, Cape Town,1996
Subjects
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Behavioural Patterns and Growth Strategies of Red Tide Organisms of the Southern Benguela.pdf
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