Mireille Consalvey PhD Thesis - University of St Andrews

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course of the day would suggest a migratory rhythm independent of light and
tidal influence. Whilst this site would require further investigation it is possible
that the increase at the start of the day reflects an attempt to maximise exposure
to lower light levels, with the subsequent increase perhaps reflecting a sequential
increase in species groups. The maximum light utilisation efficiency also
significantly varied over the course of the day, showing a similar,
but dampened,
pattern to that of light exposed cores. These results could provide evidence of a
predictive endogenous rhythm in down regulation and suggests that the cells
might be taking measures to avoid photodamage, despite a potentially damaging
migratory behaviour (i. e. remaining at the sediment surface at
high light
intensities). Further to this, it is possible that cells may be sub-cycling at the
sediment surface (Kromkamp et al. 1998), therefore enabling overall biomass to
remain high whilst protecting individual cells from prolonged exposure. Such
hypotheses are purely speculatory but would be worthy of future investigation.
5.4.3. Future Work
The variation in the migratory responses between estuaries, as well as
between days, has confin-ned that generalised migratory trends cannot be
assumed. Therefore, all examinations of microphytobenthic systems should
consider these plastic migratory responses when examining other parameters
(e. g. primary productivity; see chapter 6). The work in this chapter presented
evidence showing migration to be light and tide responsive. The responses could
further be examined through artificial manipulations. The only manipulation in
this study involved permanently darkened biofilms and a natural progression
would be to examine the artificial lighting of biofilms during the night. A series
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