Mireille Consalvey PhD Thesis - University of St Andrews

Dicl varijtion, ý in microphytobcwhic
hiofijmý
This study addressed depth changes in PPFD with no quantification of the
spectral variation. Direct measures of spectral scalar irradiance have been shown
to significantly differ from incident irradiance in microphytobenthic biofilms
(KUhl and Jorgensen 1994) and therefore future studies should account for this
variation. The absorption characters of the diatom and euglenoid biofilms will
differ according to the pigment suite of the respective groups. Future work
should examine these changes and relate to changes in the surface taxa over time
(e. g. the switch from diatoms to Euglenoid cells with increasing PPFD).
6.4.5. Do modelled rates of primary productivity correlate with actual rates of
primary productivity?
Microphytobenthic primary productivity showed a diel pattem
for both
Arlesford Creek and the Hythe, with a morning maxima in productivity declining
over the afternoon with a brief increase before nightfall. There was no evidence
of a tidal rhythm on any of the days. These patterns did not reflect changes in
biomass or diel changes in PPFD. However, the rates of productivity were at
least an order of magnitude higher in July to March, possibly reflecting ambient
light conditions. Furthermore, day 2 in 1999 had comparable PPFDs to 2000 and
biomass was comparable between years and therefore not the reason for the
lower rates of productivity in March. When primary productivity was modelled,
the patterns largely corresponded to short term changes in ambient light. This is
logical considering the general lack of variation in chlorophyll a and a and P,,,,
(Perkins pers. comm). Therefore, the model is biased towards light and due care
must be taken in modelling primary production/productivity rates. The die]
pattems obtained using 14
C make sense ecologically. Cells have no way of
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