Planktonic algae are useful as indicators of water quality because their composition and distribution reflects environmental condition in lakes. Therefore, understanding their dynamics can aid certain water quality management goals. Lake Diefenbaker is a large mesotrophic reservoir in the Canadian Prairies. Approximately 98 % of its inflow is from the South Saskatchewan River. The composition and ecology of the phytoplankton community has not been reported comprehensively since the 1980s. This is a potential problem for a reservoir with multiple end users. Therefore, I collected epilimnetic whole water samples along its length from June to October in 2011 and in 2012. I examined the phytoplankton community and related their distribution to environmental factors. A total of 72 phytoplankton genera were observed with the chlorophytes having the highest number of genera (33). The increased nutrient load and non-algal turbidity associated with high inflow from the South Saskatchewan River may be related to the dominance of the cryptophytes and bacillariophytes (together constituting ~89 % of the total phytoplankton biomass). The cryptophytes were abundant during periods of high flow rates and thermal stratification whereas the bacillariophytes were abundant during cool, isothermal conditions. Lake Diefenbaker is characterized by numerous embayments. Some of these embayments are exposed to human activities including development (housing, golf courses, marinas) and livestock operations (e.g., cattle watering). These localized activities could increase the frequency or size of algal blooms that will adversely affect the water quality. Therefore, I compared the phytoplankton community composition from eight exposed embayments, four unexposed embayments and six main channel sites. Phytoplankton community compositions were not significantly different in exposed, unexposed embayments and main channel sites (P > 0.05). High flows may have overridden localized influence from embayments. Hence, similar environmental conditions were present in the embayments and main channel. Blooms of cyanobacteria are of concern because of the potential of some genera to produce cyanotoxins. I examined cyanobacteria in Lake Diefenbaker. Cyanobacterial biomass was low in Lake Diefenbaker (< 5 %). However, I observed some potential toxin and bloom-forming genera that may threaten the water quality under different environmental conditions in the future.

Cryptophytes are free-living unicellular algae which are important for the productivity and food chain Dynamics of temperate lakes. This study provides fundamental information on the ecophysiology of two freshwater cryptophytes of different cell size, mainly in terms of growth and related factors. This thesis comprises of six chapters, three of which describe light or light-and-temperature experiments with small-scale batch cultures (Chapters. 2 to 4), one depicts a larger scale laboratory experiment simulating natural conditions (Chapter 5) and the two last (Chapters 6 and 7) are based on short-term investigations in situ. The effects of light and temperature on nutrient-saturated growth and cellular composition (chlorophyll a, proteins, carbohydrates) were studied in batch cultures. With the help of mathematical models, the physiological basis for interspecific differences of growth response was determined (Chapter 2). The cryptophyte strain L315 appeared to be a cold-water species as its optimum temperature was ca. 19°C. The strain L485 was more adapted to warm-water conditions with its optimum of ca. 24.5 °C. In respect of their growth response to irradiance, L485 can be said to be a stenotopic and L315 a eurytopic strain, as L485 shows photoinhibition soon after saturation point, whereas L315 tolerates a much wider range of irradiance. The role of changes in cellular composition is discussed. In order to explain the observed growth differences the effects of light and temperature on gross photosynthesis, respiration and hence net productivity were studied (Chapter 3). The observed respiration/photosynthesis ratios were high, as in L485 and L315 respiration accounted for 17-77 % and 14-81 % of gross photosynthesis, respectively. Under optimum conditions the respiration/Pmax for L485 was 17 % and for L315 58 %. The response of cryptophytes to chromatic light was studied by means of quantitative epifluorescence microscopy and it was found that in comparison to blue-green algae cryptophytes L485 and L315 do not gain such great adaptational advantages in terms of growth by chromatic adaptation (Chapter 4). The modest role of chromatic adaptation is discussed. The role of diel vertical migrations (DVM) in the growth of cryptophytes was studied in 4 m tall experimental columns (Chapter 5). Results revealed that by migrating into cooler, nutrient rich. hypolimnion flagellated cryptophytes can increase their growth rate under conditions where resources (light and nutrients) are spatially separated for prolonged time periods. This study also emphasizes the need for more detailed DVM studies in situ. Finally, the pattern and timing of nuclear and cellular division in two Cryptomonas species in situ was studied by means of mitotic index technique (Chapter 6) and DNA quantification (Chapter 7). The nuclear division of Cryptomonas L485 (Chapter 6) appeared to be well phased, but as in this division pattern mitosis and cytokinesis were totally overlapping, it was impossible to calculate in situ growth rates. Field observations (Chapter 7) revealed that DNA quantification by means of epifluorescence microscopy is possible from a natural cryptophyte population, but as the Cryptomonas sp. population under scrutiny was not well phased, growth rate calculation could not be carried out. The survival strategies of Cryptophytes L485 and L315 in terms of r vs. K strategies are discussed in Chapter 8. It is pointed out that, although the habitats occupied by these strains as well as some of their morphological and physiological features indicate that L485 is probably a r-strategist and L315 a K-strategist, it is not possible to draw final conclusions on the basis of this study. Light and temperature, i.e. the factors mostly studied in this thesis, are presumably not the environmental factors of greatest selective importance for these cryptophytes in natural competitive situations.

The biological significance of photosynthesis is indisputable as it is necessary for nearly all life on earth. Photosynthesis provides chemical energy for plants, algae, and bacteria, while heterotrophic organisms rely on these species as their ultimate food source. The initial step in photosynthesis requires the absorption of sunlight to create electronic excitations. Light-harvesting proteins play the functional role of capturing solar radiation and transferring the resulting excitation to the reaction centers where it is used to carry out the chemical reactions of photosynthesis. Despite the wide variety of light-harvesting protein structures and arrangements, most light-harvesting proteins are able to utilize the captured solar energy for charge separation with near perfect quantum efficiency. This thesis will focus on understanding the energy transfer dynamics and photophysics of a specific subset of light-harvesting antennae known as phycobiliproteins. These proteins are extracted from cryptophyte algae and are investigated using steady-state and ultrafast spectroscopic techniques.

The biological significance of photosynthesis is indisputable as it is necessary for nearly all life on earth. Photosynthesis provides chemical energy for plants, algae, and bacteria, while heterotrophic organisms rely on these species as their ultimate food source. The initial step in photosynthesis requires the absorption of sunlight to create electronic excitations. Light-harvesting proteins play the functional role of capturing solar radiation and transferring the resulting excitation to the reaction centers where it is used to carry out the chemical reactions of photosynthesis. Despite the wide variety of light-harvesting protein structures and arrangements, most light-harvesting proteins are able to utilize the captured solar energy for charge separation with near perfect quantum efficiency. This thesis will focus on understanding the energy transfer dynamics and photophysics of a specific subset of light-harvesting antennae known as phycobiliproteins. These proteins are extracted from cryptophyte algae and are investigated using steady-state and ultrafast spectroscopic techniques.