The effects of light, temperature and nutrients on coccolithophores and implications for biogeochemical models

Heinle, Moritz (2013) The effects of light, temperature and nutrients on coccolithophores and implications for biogeochemical models. Doctoral thesis, University of East Anglia.

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Coccolithophores are one of the important groups of phytoplankton in the global
oceans, which makes it important to know how this group will react to changes in
their environment due to climate change. Modellers already recognized their
importance and included this group independently in global biogeochemical models.
This study assesses the effect of light, temperature and nutrient availability on five
coccolithophores, performing a range of laboratory experiments. The results of these
experiments were then used to change the parameterisation of coccolithophores in
the global biogeochemical model PlankTOM10. Furthermore, the model was
validated in two ways, using a database of coccolithophore biomass measurements
from the field and measurements of surface calcium carbonate derived from satellite
Temperature effects on growth depend a great deal on the coccolithophore species.
E. huxleyi (both, a subtropical and a temperate strain) and P. carterae grew best
around 20°C, whereas G. oceanica and C. leptoporus had optimum temperatures
above 25°C and still grew well at the maximum temperature tested in the
experiments. E. huxleyi was the species with the highest growth rates (μmax=0.98 for
the subtropical strain and μmax=0.97 for the temperate), followed closely by G.
oceanica and C. leptoporus (μmax=0.91 in both species). P. carterae (μmax=0.77) had
a noticeably lower maximum growth rate than the other coccolithophores. An inverse
relationship with growth rate was found for all measured cellular components (POM,
PIC, Chl a) as well as for cell volume in P. carterae.
Coccolithophores are good competitors at high light intensities, having optimum
growth light intensities above 180 μmol photons m-2 s-1. The temperate strain of E.
huxleyi and the species G. oceanica showed the lowest optima at 350 μmol photon
m-2 s-1. C. leptoporus (Iopt=500 μmol photon m-2 s-1) and P. carterae (Iopt=600 μmol
photon m-2 s-1) had higher optimum growth light intensities and the subtropical strain
of E. huxleyi (Iopt=900 μmol photon m-2 s-1) grew best at the highest light intensity
applied in this study. Only one strain of E. huxleyi showed light inhibition in its
photosynthetic activity that was well above the detection limit in P-I curves up to
2000 μmol photons m-2 s-1. Apart from a well-known decrease in Chl a/C ratio with
increasing light intensity, little variation in the concentration of cellular components
(POM, PIC) was observed.
Nutrient experiments were carried out in a chemostat with two strains of E. huxleyi
and one G. oceanica. Phosphorus limitation led to an increase in cell volume (112-
157%) and particulate organic carbon (21-54%) in E. huxleyi and G. oceanica,
relative to cultures grown under nitrogen limitation. Comparison of uptake rates for
phosphate and nitrate with other phytoplankton groups showed that both species are
very good competitors for phosphate and relatively poor competitors for nitrate.
The initial PlankTOM10 model simulation overestimated biomass compared with a
new observational database, and underestimated surface calcium carbonate compared
with satellite data. Changing the coccolithophore parameterisation in PlankTOM10,
based on the laboratory results, did not lead to significant improvements relative to
the observations. However, the response of the model to the parameter changes could
be explained either directly from the changed parameters, or indirectly from changes
in the model ecosystem.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Users 2259 not found.
Date Deposited: 11 Jun 2014 09:13
Last Modified: 11 Jun 2014 09:13

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