Mireille Consalvey PhD Thesis - University of St Andrews

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Cells becoming stressed over exposure period
Honeywill (2001) implicated low biomass as being a potential cause of high
F, IF,, 15 measures and recorded F,, 15 values of < 150 fluorescence units (FMS2) to
be associated with unusually high FIF,, 15
. At the start of these studies the F, 15
values were within this range. It therefore possible that as the cells migrated to
the sediment surface the associated increase in F,, '5 resulted in a more accurate
determination of FIF,, 15 and that the decline in the maximum light utilisation
efficiency was an artefact of the fluorometer rather than a physiological
phenomena. However, over a light exposure period there are likely to be several
stresses for microphytobenthic cells (e. g. photodamage, heat, and desiccation). It
is therefore also possible that the decline was associated with an
increase in
stress for the population. Cores that were flooded (Tay and Eden February)
exhibited a significant increase in this parameter, but it is not possible to attribute
this to a removal of the stresses or the decrease in F,, 15
.
The maximum light utilisation efficiency of cores from the Eden (April)
did not significantly change over the light exposure period. These cores were
subject to the same, if not more stresses (evidence of dewatering) than the Tay
and Eden (February), but had a significantly higher F. 15 at the start of the
experiment (> 150 fluorescence units). Therefore, it is most likely that the
decreases seen are a consequence of the increasing Fo 15 yield. Cores from the
Eden (April) that were in the light had significantly lower maximum light
utilisation efficiencies than cores in the dark. This might be indicative of stress,
but again the problems associated with a lower F, 15 yield cannot be eliminated.
There were no significant differences between the maximum light utilisation
efficiencies of cores that were in the light exposed and light submerged
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