Mireille Consalvey PhD Thesis - University of St Andrews

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and with a 95 % reduction in biomass it was unlikely that cells migrated from
under the site. Therefore, results would suggest that the incoming tide brought an
innoculurn of cells. Subsequent to this it is not possible to determine if the
biomass increase was attributable to the doubling rate of the cells (under
favourable conditions diatoms can exhibit a daily doubling rate) or the fresh
deposition of cells on each tide; both could affect the rate of recovery.
In the laboratory study the chlorophyll a content had significantly
increased by day 3 and reached a maximum after 13 days. At the start of the
study there had been significantly more chlorophyll a in the deeper layers which
could be attributed to settling of PIB. By day 13 there was significantly more
chlorophyll a in the top layers, attributable to settling and colonisation of cells
from the water column. At this stage the microscale distribution and content of
biomass was characteristic of those microphytobenthic biofilms previously
described (e. g. PROMAT Final Report; Wiltshire et al. 1997; Honeywill 2001;
Kelly el al. 2001) with a concentration of biomass in the upper layers of the
sediment followed by a linear decrease with depth. However, after 45 days there
was no significant concentration of biomass in the upper layers, or decrease with
depth, and the reasons for this will
be discussed below.
The chlorophyll a content, as well as rate of biomass increase, differed
when expressed for different depth intervals. The inclusion of successively
deeper layers serves to dilute the biomass and therefore reduce the chlorophyll a
content (also described in Kelly et al. 2001). Therefore, the scale at which the
biofilm is examined has implications for cross comparing biofilm growth studies.
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