Mireille Consalvey PhD Thesis - University of St Andrews

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cells as they emerge and the synchronicity of the migratory response. Differences
in in situ migratory patterns could be attributed to shifts in light: dark phasing
with high: low tide (Round and Palmer 1966).
Natural biofilm communities incubated under constant light vs. constant
dark demonstrated a general lack of movement under dark conditions but
maintained rhythms under constant light (Round and Palmer 1966; Happey-
Wood and Jones 1988). Dark samples re-expressed migratory rhythms when
exposed to light and these rhythms appeared no different from samples incubated
under constant light. However, Ser6dio et al (1997) found that cells in the dark
can express a migratory rhythm and that this can be maintained for several days.
Therefore, the nature of the migratory rhythm may be system specific. Light
intensity and wavelength have both been proven to have a profound influence on
speed and migration (Hopkins 1966) with lights of a shorter wavelength (e. g.
blue) inducing maximal migration.
Perkins (1960) suggested downwards migration would not occur until
there was sufficient water coverage to reduce the irradiance below a critical level
(see also Hopkins 1963,1966; Kingston 1999). However, researchers including
Faur6-Fremiet (1950), Palmer and Round (1965), Round and Palmer (1966), and
Happey-Wood and Jones (1988) have shown migration to occur before tidal
inundation, thus indicating a tidal periodicity. The darkness imposed by turbid
waters may transform a fundamentally light (or diurnal) driven rhythm into a
tidal one. In the absence of environmental cues the rhythm remains diurnal rather
than tidally influenced.
Cells also maintain migratory rhythms when any tidal influence is
removed (Round and Palmer 1966). Ser6dio et al. (1997) deten-nined cells from
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