Mireille Consalvey PhD Thesis - University of St Andrews

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sediments over the exposure period, leading to an increase in concentration but a
decrease in content. Pinckney et al. (1994) discussed how the uneven nature of
the sediment surface makes it impossible to sample sections of known volumes,
the weight of the surface section was always significantly higher, which was
attributed to the difficulty associated with defining a flat surface. Therefore, they
made the recommendation that chlorophyll a always be non-nalised to weight.
It is essential to consider changes in cell distribution with depth. The lens
tissue technique has been used extensively to monitor changes in species
composition over time (e. g. Eaton and Moss 1966; Round and Palmer 1966) but
whilst providing useful taxonomic inforination this technique does not account
for any non-motile components of the microphytobenthic consortia, subsurface
cells nor changes in the topography of the sediment biofilm. Paterson (1986)
pioneered the use of LTSEM to visualise changes in species composition over
time. LTSEM enables samples to be examined 3-dimensionally and in some
cases subsurface cells can also be visualised. LTSEM analysis often reveals high
levels of spatial microheterogeneity, however, the reasons for this are unclear
(Janssen et al. 1999).
Photoinhibition has rarely been recorded in intact microphytobenthic
biofilms (Blanchard and Cariou LeGall 1994; Barranguet et al. 1998; Kromkamp
et al. 1998; Dodds et al. 1999). It has been hypothesised that the overall
efficiency of the biofilm is maintained through the vertical cycling of cells at the
sediment surface (Kromkamp et al. 1998). Therefore, cells are able to optimise
their exposure to light whilst minimising time spent at potentially damaging
irradiances (Round and Palmer 1966; Barranguet et al. 1998; Kromkamp et al.
- Perkins et al. 2001).
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