Mireille Consalvey PhD Thesis - University of St Andrews

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Zingmark (199 1) found the rates of primary production at low tide to be double
those at high tide.
1.6.5. Migration within the biofilm
Sub-cycling of cells at the sediment surface has been hypothesised but
not yet shown by Kromkamp et al. (1998). Microcycling of cells within the
upper layers of the biofilm could enable cells to avoid over exposure to
potentially damaging light levels, high temperatures, desiccation and grazing. A
scenario has been proposed (Kromkamp et al. 1998; Paterson and Underwood
pers. comm) whereby cells are able to stratify within the upper layers of the
sediment based upon the prevailing environmental conditions. The adaptation of
photosynthetic organisms to their environment is a well documented
phenomenon (e. g. the different canopy layers of the rainforest) but the evolution
of motility has enabled microphytobenthic cells to determine their position
within the light field and in doing so positively respond to competition for
resources. Such behaviour not only confers an evolutionary advantage for the
cells, but enables far higher rates of biofilm productivity to be achieved than
would be predicted from the cells themselves. If this hypothesis is verifiable the
biofilm may be considered as being more than the sum of its parts.
1.6.6. An evolutionary perspective
Vertical migrations are widely described for a diverse range of
microphytobenthic taxa, the ubiquity of these behaviours suggests that these
actions must confer some evolutionary survival advantage (Cohn and Disparti
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