Mireille Consalvey PhD Thesis - University of St Andrews

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microphytobenthos. Endogenous rhythms have also been shown to persist in the
absence of various stimuli (e. g. dark, tide) and rhythmic migrations have been
shown to persist in laboratory systems for between 3 (Ser6dio et al. 1997) and 21
days (Paterson 1986).
Migratory rhythms have been shown to remain tidal under constant light
conditions in the laboratory, demonstrating that light alone is not sufficient to
keep cells at the sediment surface (Palmer and Round 1965). Under constant
laboratory conditions, some microphytobenthic assemblages have demonstrated a
daily shift to reflect the tides, which became rephased to account for the evening
low tide (Happey-Wood and Jones 1988). Ser6dio et al. (1997) demonstrated a
strong endogenous tidal migratory rhythm in cells kept under dark conditions in
the laboratory. Callame and Debyser (1954) showed that a tidal migration rhythm
was only maintained for one day in the laboratory if the samples were not wetted,
and concluded that for any migratory rhythm to remain tidal a water cue was
needed.
In contrast, diumal migratory rhythms have been reported by Palmer and
Round (1965) and Round and Palmer (1966) for cells kept under constant light
conditions in the laboratory. Happey-Wood and Jones (1988), despite finding
that the rhythm was primarily tidal, also demonstrated that cells migrate down at
times of darkness and any endogenous tidal rhythm is rephased according the
illumination status at the site.
Palmer and Round (1965) and Hopkins (1966) described diatoms to have
a self-sustaining migratory rhythm that follows daylength, but is affected by a
superimposition of a tidal rhythm. To account for patterns in migration, Hopkins
(1966) developed a model that incorporated rhythms in phototaxy and motility.
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