Mireille Consalvey PhD Thesis - University of St Andrews

Ctlai,! ': ý ý,
-II(
Icticral Disctt,,,
-,
sion
Resolution Fluorescence Imaging and is further evidence that cells sub-cycle
(Perkins et al. submitted).
8.2. Sediment biofilm light climate
Fibre-optic sensors were constructed and these were deployed over a diel
period for the first time. The light attenuation co-efficient (k) was determined to
vary with site. Reasons for the variation between sites were not
determined, but
are likely to reflect the geological characters of the site as the site with the
highest k values also had the greatest proportion of particles -- 63 ýtm. Generally
the highest k values were also associated with highest biomass. To accurately
account for PPFD in primary productivity models therefore requires that k be
calculated for each site, and for each study, as k was demonstrated to vary from
year to year.
In all cases, 90% of the surface PPFD had been attenuated by 400 ýtm,
and in many cases this occurred before 200 ýtm. There are clear
implications for
the depth of light penetration on migration. During daylight hours cells migrating
from deeper than 200 ýim will be experiencing no or very little light; therefore
light will only act as a stimulus for cells in the photic zone. Cells that respond to
light will either pennanently reside in the photic zone or will have an additional
endogenous geotactic response to bring them into the photic zone.
The light attenuation co-efficient, k, was also shown to significantly
change over the day. This has never been previously reported and
has far
reaching implications. On the basis of these findings not only must k be
determined for each site but also monitored over the course of a day to accurately
model changes in PPFD with depth over time. The changes in k seemed to
236