Mireille Consalvey PhD Thesis - University of St Andrews

Chapter , -11111 f'ol-ImItio I alld (h"\ ýýIoplilcnl
demonstrating the importance of biological processes in a system once only
considered at a physical level (Montague 1986).
Description of site/cores
In both studies biomass changes were visible to the naked eye within a
few days (indicating ýý. 104 CM-2 Cells; Paterson 1989), and confirmed by
pigment/LTSEM analyses. The colouration of sediments has often been used as
an indicator of taxonomic group (e. g. Under-wood 1997; Paterson et al. 1998) and
in both studies the appearance of a golden brown film indicated the presence of
diatoms. Biofilm growth started from patches that merged to form a larger
biofilm. The source of these patches was unknown, though believed to be from
the water column. The laboratory experiment would seem to support the
hypothesis that the water column can successfully seed a microphytobenthic
biofilm. The cues for these patches remains unclear; in both studies the
sediments were assumed to be homogeneous at the start.
Towards the end of the laboratory study the biofilm started to blister with
oxygen bubbles and the small current generated by the flow-through water
system removed some of the biofilm. In a natural system with grazers and tides it
is rare that a biofilm would develop to this stage.
Water content
Biofilms have been described as biologically stabilised water and
significant changes in water content may be associated with biofilm growth. The
physical removal of the top layer of sediments in situ led to the formation a slight
drainage ditch, as well as exposing more compact subsurface sediments; this
80