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The following is a general overview of the current interests and research activities of the Harrison lab. Please follow a person's link for updated and more detailed research descriptions.

Factors influencing phytoplankton bloom dynamics in the Queen Charlotte Islands (Haida Gwaii)

(with Heather Toews, M.Sc. candidate)

This project is being performed in collaboration with Parks Canada. Field studies in the area of Gwaii Haanas National Marine Park Reserve are planned for the summers of 2001 and 2002, where large algal blooms have been detected by satellite in recent years. The aim of this study is to determine which algal species are present during blooms, as well as what chemical and physical factors may be responsible for bloom initiation, maintenance, and decay. In addition, optical properties of surface waters will be measured and used to  ground-truth satellite observations (including chlorophyll a concentration, total suspended sediments, and chromophoric dissolved organic matter [CDOM]), in an effort to estimate and map primary productivity in the coastal ocean.


Ecophysiology of Pseudo-nitzschia sp. in the northeast subarctic Pacific

(with Rana El-Sabaawi, M.Sc. candidate, Adrian Marchetti, Ph.D. candidate)


The diatom Pseudo-nitzschia sp. isolated from a High Nutrient Low Chlorophyll region (Station P, 50oN, 150oW) shows high growth rates when iron is present in Fe addition experiments. This diatom appears to be a permanent feature of the oceanic phytoplankton community in this region, but does not figure prominently in numbers or biomass in the absence of this trace nutrient. How this diatom persists under suboptimal conditions (low light, low Fe) and how it responds to the presence of a limiting nutrient(s) is interesting in terms of  understanding how nutrients are cycled in this region, and how iron additions impact the ecology of phytoplankton in a low-light, low trace metal environment.

Response of Phytoplankton to Variability in Physical and Chemical Factors off Vancouver Island

(with Shannon Harris, M.Sc. candidate)

The Global Ocean Ecosystem Dynamics Program (GLOBEC) will examine how and why living marine resources are affected by variability of their physical oceanic environment. More specifically this project will determine the response of commercial fish and plankton populations off the western Canadian continental shelf and slope to variability of circulation and water properties at seasonal to decadal time scales. Variations in phytoplankton primary production, biomass and composition, as mediated by physical transport and nutrient supply and how these variations affect food availability for salmon will be examined. Combined with time-series data sets from other locations this work will evaluate large-scale coherence of year-to-year "anomalies" between various variables and between widely separate locations. This data set is essential to validate the physical/plankton/fish model being developed for the western continental margin of Vancouver Island. This model will be used to forecast ecosystem production trends based on physical forcing of the lower trophic levels, and natural and anthropogenic forcing of the higher trophic levels. Three cruises are scheduled for 1997 and for 1998 to study seasonal phytoplankton variations.

Microbial Ecology in the Subarctic North Pacific Ocean

(with Nelson D. Sherry, Ph.D. candidate)

This study is part of the Canadian Joint Global Ocean Flux Study (CJGOFS), and it is evaluating the role that heterotrophic bacteria play in the oceanic carbon budget of the Subarctic North Pacific and determining the factors that control bacterial abundance, growth, and remineralization rates. Preliminary results indicate that there is a trend toward higher bacterial viability with depth. Along Line P (a 2000 km normal-to-shore line) bacterial productivity, in the surface mixed layer, decrease 3- to 10-fold depending on the season. The decrease does not coincide directly with indicators of phytoplankton iron limitation. Bacterial respiration appears to decrease more quickly than productivity indicating higher carbon assimilation efficiency further from shore. Heterotrophic bacterial numbers do not correspond to productivity measurements. Bacterial production appears to be carbon limited and may respond negatively to the addition of iron.

Effects of Iron and Light Limitation on the Photosynthetic Apparatus of a Marine Diatom

(with Robert Strzepek, Ph.D. candidate)

Light increases cellular iron (Fe) requirements for phytoplankton because it affects the functional organization of the photosynthetic apparatus. Phytoplankton acclimate to low photon-flux densities by changing pigmentation and abundance and stoichiometry of Fe-rich electron transport components and reaction centres. Photoacclimation is widely observed in oceanic phytoplankton and it allows algae to maintain fast rates of photosynthesis. The costs of such an acclimation are predicted to be high when light levels are near the compensation irradiance. There is about a 50-fold increase in Fe demand for photolithotrophic growth at low light compared to full sunlight. We are presently testing the effects of both Fe and light limitation using the marine diatom Thalassiosira weissflogii grown over a broad range of irradiances and Fe concentrations. The results show that the Fe content of this photoautotroph increases remarkably under low light. Part of light-induced increase in Fe quota can be accounted for by changes in the Fe-containing photosynthetic component, confirming that photoacclimation imparts a significant Fe requirement.

Nitrogen Isotope Fractionation in Phytoplankton: Variations in Light and Temperature Conditions

(with Joe Needoba, PhD candidate)

This project involves the study of the stable nitrogen isotope (15N) and its use as a tool in oceanographic studies. Specifically, I am looking at the fractionation associated with the uptake and assimilation of inorganic nitrogen by phytoplankton. This process has important implications for how stable nitrogen isotope data is interpreted, as well as providing interesting insight into nitrogen assimilation in phytoplankton.

The proposed study intends to determine the magnitude of nitrogen isotope fractionation for 3 species of phytoplankton grown on NO3- in ecologically relevant growth conditions. The effects of species type, growth rate, and internal nitrogen pools, will be investigated. The results are intended to identify the important physiological mechanisms responsible for nitrogen isotope fractionation during growth on nitrate.

measure the fractionation associated with phytoplankton growing on NO3- during ecologically relevant growth conditions. Under low light and low temperature conditions phytoplankton cells grow more slowly. Variation in fractionation associated with changes in these conditions has been reported (Wada, 1980), although is not confirmed (Montoya and McCarthy, 1995).

A cell's ability to store internal nitrogen varies among phytoplankton taxa, and varies depending on growth conditions (Dortch et al. 1984). This may impact the amount of fractionation, since the d 15N of the internal pool could increase, and fractionation will be expressed if nitrogen is released before it becomes assimilated. Additionally, the cultures will be monitored for release of nitrite, ammonium, and dissolved organic nitrogen (DON) in order to determine if nitrogen is being released from the cell in another form than nitrate. An isotope tracer study, using 13N nitrate, is also proposed. This will help determine the amount of NO3- that is released from the cell, rather than being incorporated after uptake.



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