The structure and function of microphytobenthic biofilms
Abstract
Microphytobenthos
are the dominant
primary producers on estuarine
mudflats playing a
key
role
in the functioning
of the ecosystem.
Studies into
microphytobenthic ecology
have
previously
been limited by
scale
but the advent
of
fine
scale analysis
techniques (gm)
as well as non-destructive sampling
has
enabled the system to be
examined at a
level
not previously possible.
This
study
examined the formation,
structure and
function
of microphytobenthic
biofilms
using non-destructive
(remote
sensing
by PAM fluorescence; fibreoptic light
microprofiling) and
destructive (cryo-freezing
and
Low temperature scanning
electron microscopy) sampling.
Many
microphytobenthic organisms are motile and
have
evolved complex
migratory strategies.
Microphytobenthic
migratory patterns are widely
described
but
much remains to be
elucidated about the controlling
factors. The fluorescence
parameter
F015 (minimum fluorescence
yield after
15
minutes
dark
adaptation)
was used to monitor short-term changes in
biomass
at the sediment surface.
Light, tidal state, endogeny and combinations thereof were all shown to control
migration,
demonstrating that predictable migratory rhythms cannot
be
assumed.
Microscale
sectioning
showed that chlorophyll a was always
concentrated
in the top 400
gm
(the
photosynthetically active
biomass). Clear
migratory patterns were not
detected
using microscale sectioning therefore
indicating that migration occurs over a scale < 400gm.
Despite
no changes in the
chlorophyll a content
in the surface
layers, LTSEM
analysis
demonstrated
diurnal taxonomic shifts providing circumstantial evidence that
microphytobenthic cells sub-cycle at the sediment surface to optimise
fitness.
The light
extinction co-efficient
(k)
of microphytobenthic
biofilms
significantly vaned with site, assemblage and also over time. 90%
of the surface
PPFD had
always
been
attenuated by 400, and in many cases before 200.
Traditional
microphytobenthic primary productivity models
do
not account
for
changes
in the spatial and temporal distribution
of
biomass
or
light
attenuation and
therefore their applicability to the real situation may
be limited.
Type
Thesis, PhD Doctor of Philosophy
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