Mireille Consalvey PhD Thesis - University of St Andrews

Chapici 4 Laborator\ hivest' jgauml I. Into T111C ropliviobenthic,
compared to other fluorescence vanables (F,,, Fn' and F'). F, also showed the
least amount of species specific variation. Honeywill (2001) found a stronger
correlation between F, 15 and chlorophyll a than F,, 15 and chlorophyll a.
Despite the fact that linear relationships have been detennined to exist
between chlorophyll a and dark level minimum fluorescence (Ser6dio el al.
1997; Honeywill 2001; Ser6dio et al. 2001; Honeywill et al. 2002) the slope and
intercept of the line are variable (Ser6dio et al. 1997). Therefore it is essential to
appreciate that whilst a change in minimum fluorescence may be related to a
proportional change in chlorophyll a, the chlorophyll a content per se cannot be
determined using this method.
2) The photic depth is shallower than the depth of migration
Ser6dio et al. (1997) estimated the photic depth of the intertidal
sediments in which he measured fluorescence to be 270 gm. This is shallower
than the depth over which cells are reported to migrate (Palmer and Round 1965;
Paterson 1986; Pinckney 1994; Paterson et al. 1998; de Brouwer and Stal 2001;
Kelly et al. 2001). Kromkamp et al. (1998) determined that the fluorescence
signal of microphytobenthic cells is only detectable in the upper 150 [tm.
Furthen-nore, the fluorescence equipment that was used in this chapter (FMS2)
has a blue measuring beam; blue light is attenuated more rapidly than other
wavelengths in sediments (Lassen et al. 1992; MacIntyre and Cullen 1995;
Kromkamp et al. 1998), therefore the measuring beam will not penetrate as deep
as other wavelengths.
Fluorescence techniques are limited to the photic zone and consequently
only the biomass that is potentially photosynthetically active can be measured.
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