OBJECTIVE:
Microphytobenthos biomass and primary production is difficult to measure because of the patchiness in occurrence and the variable photosynthesis rates during a tidal cycle. This short-term variation in photosynthesis may be due to photoinhibition, nutrient limitation (especially CO2 availability) and vertical migration. The aim of this project is to estimate primary production by microphytobenthos using variable fluorescence techniques and to understand the mechanisms causing short-term variability in the photosynthetic process. This project is closely linked with project 02MM18 and 98MM04, but will study the physiological processes behind the variability in PSII electron transport as estimated using a PAM fluorometer, using techniques developed in the photobiology project MM 98MM04 in combination with statistical analyses of spatial variability.
APPROACH: Photosynthesis will be measured in situ on the intertidal mudflats using a portable PAM. These measurements will be correlated with other methods (MIMS, 14C-uptake) to estimate photosynthesis. Further measurements will involve fluorescence excitation emission spectra in order to establish the true optical cross sections of PSI and PSII. From these measurements it will be investigated which proportion of the light absorbed by the algae will go to PSII. Sensitivity to photo inhibition will be studied using high and low light laboratory growth measurements, and the photon dose per molecule of chlorophyll needed to induce photoinhibition will be determined for different species and natural assemblages. Relaxation studies will be performed to distinguish between the extent of dynamic vs chronic photoinhibition. To further investigate the effect of vertical migration and total daily light dose on the maximum biomass (carrying capacity) and daily primary production mesocosm experiments will be carried out. These measurements, combined with irradiance data, will give a better understanding of the variability in photosynthetic characteristics observed in the field during a tidal cycle.
PLANNING 2003:
In 2003 emphasis will lie on the statistical analyses of spatial distribution and mesocosm experiments. These analyses will be performed on already existing datasets and at several sites within the Westerschelde estuary, and should give an indication of which parameters (like position relative to the low water line) influence MPB biomass and distribution. Experimental work will focus on measuring the optical cross sections of PSI and PSII from fluorescence emission excitation spectra and PSI absorption changes. Mesocosm experiments will be carried out, using autoclaved natural sediments to remove grazers, to investigate the effect of tide, vertical migration and total daily light dose on the maximum biomass.
This project will finish in 2003 and papers and a PhD thesis will be written.
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