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Background:
The
oceans contain only about 0.5% of total global
biomass of primary producers. However, they provide a similar amount of
total annual production to that on land and turnover
times for organic matter is 1000-times faster in
marine in comparison to terrestrial ecosystems.
Therefore grazing by zooplankton is
disproportionally important and competition among
grazers is high.
Image by
Glynn Gorick
All organisms release chemicals into
the surrounding environment and at small spatial
scales the high viscosity aqueous environment allows
the persistence of chemical gradients and the
reliable transmission of chemical cues. As a
consequence chemosensory systems have evolved in a
diverse range of marine taxa. in the vast 3D marine
environment non-visual planktonic-grazers rely on
infochemical
(information conveying chemical)
signals
to locate prey or mates. Conversely,
intense grazing pressure has lead to
the evolution of defence mechanisms in phytoplankton.
Dimethylsulphoniopropionate (DMSP)
is an abundant intracellular metabolite found in
many phytoplankton. Algal DMSP can be converted into
the climatically-relevant trace gas dimethyl sulfide
(DMS), a process accelerated by natural senescence,
viral lysis or grazing.
DMS and DMSP have been shown to
act as infochemicals in a wide variety of species across a
range of spatial and temporal scales from bacteria
to seabirds. Microzooplankton and copepods are important grazers
of phytoplankton primary productivity. The ability
to detect and respond to DMS and DMSP, associated
with rich prey patches, may provide vital foraging
cues.
In this project we will assess the
role of DMS and related compounds in mediating
trophic interactions between small phytoplankton,
microzooplankton and copepods. A series of
laboratory and field experiments will determine
grazing rates and DMS-production following
microzooplankton grazing on different
phytoplankton species. The foraging responses of
carnivorous copepods to the release of these
infochemicals will be assessed.
The project includes a tied PhD
Studentship aiming to mathematically model DMS-mediated
trophic interactions.
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