Mireille Consalvey PhD Thesis - University of St Andrews

Chapici_6
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a sampling depth of 150 ýtm has been proposed (Kromkamp et al. 1998). It is
further possible that the assemblages were responding to different conditions in
the respective studies as the migratory response has been shown to to be plastic.
The increasing use of fluorescence to estimate primary production rates
from the ETR/relative ETR (see chapter 1) may be fatally flawed through the
assumption of constant PPFD in the upper biofilm layers. The vertical
stratification of cells within the biofilm, shown in this and other studies, makes it
impossible to predict the light climate that all cells are exposed to. Perkins et al.
(2001; 2002) demonstrated F,, 'IF,, ' to deviate from the expected inverse
relationship with PPFD, owing to cells migrating into the sediment and not being
exposed to the surface PPFD, therefore leading to an overestimation of ETRmax-
The daily changes in taxa at the sediment surface (from both endogenous
migration and in relation to ambient light) suggest that changes in productivity
could be indicative of different taxa. Therefore, where possible, taxonomic
changes should be monitored however, the disadvantage to this approach is that
measurements are generally destructive.
6.4.7. Future studies
Where possible, future work should increase the number and times of
sampling to provide a more detailed examination of changes in biomass/light
attenuation co-efficients. It is possible that with more data points some genuine
trends relating light attenuation co-efficient with biomass might
be discerned.
This relationship could also be tested by laboratory manipulation of biomass on
artificial b1ofilms.
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