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Marine phytoplankton primary production and ecophysiology using chlorophyll-A fluorescence

Cosgrove, Jeffrey John (2007) Marine phytoplankton primary production and ecophysiology using chlorophyll-A fluorescence. PhD thesis, Murdoch University.

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Marine phytoplankton ecophysiological state and primary production measurements have typically been controversial due to potential impacts of measurement techniques. Advances in chl-a fluorescence techniques have provided a means for rapid, non-invasive measurement of electron transport through photosystem 2 (PSII) in dilute phytoplankton suspensions. While studies on higher plants have outlined a close relationship between PSII electron transport and carbon fixation, results from studies on microalgae reveal significant variations in the relationship.

Three species of phytoplankton representing three major taxonomic groups of the marine phytoplankton were used in this study: (1) Chaetoceros muelleri CS176 Lemmermann (Bacillariophyta), (2) Isochrysis galbana CS177 Parke (Haptophyta) and, (3) Nannochloropsis oculata CS179 (Droop) Hibberd (Ochrophyta, eustigmatophyte). Each species was cultured in semicontinuous culture and primary production was estimated using oxygen evolution and carbon fixation techniques and compared against predictions based on chl-a fluorescence measurements. It was found that predicted values of primary production both under-estimated and overestimated actual carbon fixation measured via radioisotope (14C) techniques. This variation was primarily explained by probable errors in the assumed values for PSII density. The relationship between oxygen evolution or carbon fixation with chl-a fluorescence-derived measures was commonly linear below the light saturation parameter, with a departure from linearity occurring at higher irradiances. This departure from linearity was greatest in cultures adapted to low light conditions. At higher light intensities alternative electron pathways such as the Mehler reaction and/or chlororespiration are likely to be more active in low light-adapted cultures, leading to this greater non-linearity.

Chl-a fluorescence measurements were also found to be a useful in characterising ecophysiology using photosynthesis-versus irradiance curves. However, an important caveat on this is the measurement of PSII density ([eta]PSII) rather than use of an assumed value as changes in [eta]PSII can have a profound impact on light curve parameters.

A field study in Fremantle Harbour found a healthy (negligible nutrient starvation), diatom dominated, phytoplankton community. Results suggest that phytoplankton are able to begin boosting photosynthetic capability just prior to morning twilight. Waters in the harbour were well mixed via tidal motion and substantial midday photoinhibition was not observed. Data suggest levels of primary production at the mouth of the harbour are similar to those of coastal waters in the plume of the Ocean Reef wastewater outfall.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Supervisor(s): Borowitzka, Michael
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