Mireille Consalvey PhD Thesis - University of St Andrews

Colloidal carbohydrates
13iof-11111
loill"'Itioll and dQ:
\CIoj-, jlwllt
The colloidal carbohydrate contents obtained in the laboratory study were
over an order of magnitude greater than values obtained by Grant et al. (1986)
and Grant and Gust (1987), but within the ranges detected by Underwood and
Paterson (1993), de Brouwer and Stal (2001) and Kelly et al. (2001) and
therefore were considered representative of values found in situ. Underwood and
Smith (1998) described an increase in colloidal carbohydrates over the
ernmersion period, with a subsequent decline as they are washed away on the
incoming tide. The lack of tides in the laboratory system may lead to elevated
levels of colloidal carbohydrate. It is unknown if any were lost to the water
column through diffusion or by the small currents generated in the flow through
tanks.
The colloidal carbohydrate contents did not follow the same trend as
chlorophyll a. After 3 days there was a reduction in the colloidal carbohydrate
content. The reasons for this were unclear but it is possible that bacterial activity
degraded those that were present already (Decho 1990), and it was only by day 7
that production of colloidal carbohydrates was greater than consumption.
The distribution of colloidal carbohydrates remained concentrated in the
upper layers of the b1ofilm/sediment over the first 13 days. However, after 45
days there was no significant depth effect. This pattern was reflected by the
chlorophyll a content and these distributions suggest that cells may have been
migrating/moving throughout the top 2 mm. The biofilm was dominated by
motile fon-ns (mainly naviculoid cells), which would support this premise.
83