published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

This thesis develops, validates and applies an empirical model that provides the first spatially explicit estimates of gross and net phytoplankton production in Lake Victoria. Gross and net phytoplankton production are in turn used to estimate the maximum sustainable yield (MSY) of Lake Victoria's fishery following an empirical formula and the carbon efficiency transfer method. Chapter 2 presents results from three inshore areas where diurnal and sub-seasonal gross and net phytoplankton production was derived using an adapted version of the phytoplankton production model developed by Fee (1990). Spatial and temporal trends of chlorophyll (chl), PI parameters, the vertical attenuation of PAR (kPAR), Secchi depths (SD) and respiration rates are identified. kPAR and SD are highly correlated to chl within the euphotic zone, as well as to each other. Furthermore, the two PI parameters, PBM and aB, exhibit a strong linear relationship and both decline along an increasing chl gradient, presumably due to increased light-limitation, a taxonomic shift from diatoms to cyanobacteria with increasing chl as well as an increased need for biologically fixed nitrogen. These hypotheses are supported by observed synchronous changes in the PSII:PSI ratio of phytoplankton and changes in the chl-specific attenuation of PAR (kchl). Relationships are also derived between biomass-specific respiration rates (RB) with chl and PBM; similar to PI parameters RB decreases with increasing chl. Owing to these correlative trends, only one parameter is required to estimate gross phytoplankton production through the empirical model developed in this thesis. The empirical model predicts that gross phytoplankton production increases in a near linear fashion between chl of 0 to 10 mg. m-3, begins to flatten out as chl approaches 20 mg. m-3 and then slightly decreases when chl exceeds 40 mg. m-3 where the maximum PPG of 13. 1 g O₂. m-2. day-1 is reached and is in close agreement with a theoretical argument proposed by Talling (1965). Areal respiration and consequently net phytoplankton production are sensitive to chl within the mixed layer as well as mixed layer depths. Overall, the lakewide averages of gross and net phytoplankton production are 9. 68 and 2. 2 g O₂. m-2. day-1 respectively. Significant temporal variability was observed on sub-seasonal scales within the inshore of Lake Victoria, and changes in limnological parameters coincided with changes in water column temperatures in each of the three bays. In Fielding Bay, the availability of meteorological data revealed that strong nocturnal wind events decreased both the water column temperature and chl, while both parameters generally increased in the absence of any such wind event. Lateral exchange of water with deeper areas through strong wind events essentially flushes Fielding Bay causing the observed decreases in both the water column temperature and chl; this hydrodynamic event also influences other limnological parameters according to their respective correlative regression equations with chl. Spatial trends were also observed between inshore areas. The deepest area, Napoleon Gulf, has the lowest values of chl while the shallowest area, Inner Murchison Bay, has the highest chl as the mean depth of a bay sets an approximate upper limit on chl. With respect to diurnal variability, PI parameters decline through the day, kPAR increases over the day and no statistically valid trends were ascertained for chl and RB. Chapter three examined spatial and seasonal patterns of chlorophyll fluorescence, temperature, dissolved oxygen and water transparency from four lakewide cruises. Significant spatial variability of each parameter confirmed that lakewide data is required to generate spatially explicit estimates of phytoplankton production. Complex patterns in the thermal structure during each cruise illustrated that physical processes in Lake Victoria are at times more complex that a previously stated unidirectional hypothesis of warm water in the north and cool water in the south (Spigel and Coulter 1996), and these patterns influence spatial patterns in dissolved oxygen and Secchi depths. Similar to Chapter 2, estimates of chl within the mixed layer were highly correlated to mixed depths, while lakewide averages of chl are lower than previously reported offshore values (Mugidde 1993, 2001).

Processes regulating the growth and successional pattern of phytoplankton and the production of odour compounds in lakes of coastal and interior British Columbia were examined. An emphasis was placed on the role of nutrients, the role of size in determining nutrient deficiency, and the importance of winter for understanding the functioning of coastal lakes. Although the study lakes were all phosphorus limited (TN:TP molar ratio >22), plankton, especially the greater than 3 pm size fraction, were often nitrogen deficient. This demonstrates the importance of nitrogen as a growth regulating nutrient for larger plankton in these lakes. Seasonal patterns of productivity varied among lakes, and Maxwell Lake was found to reach maximal photosynthetic rates in February. Lakes without a dominant seasonal physical influence (e.g. ice-cover) and those subject to short-scale stochastic events that play dominant roles may not have their "successional clock" set. This can lead to an apparent chaotic seasonal pattern of species distribution. In coastal lakes the lack of strong seasonal patterns is more likely to occur in lakes with lower nutrients (e.g. <10 pg TP-L-') than in lakes with relatively high nutrients (>I5 pg TP.L-') because of the seasonal cycling of nutrients within eutrophic lakes. The origin of odours in drinking water was examined from nineteen lakes and reservoirs to determine links between limnological variables and classification and intensity of odour. Total phosphorus (TP) was the best single predictor of odour intensity. Vegetation and grassy odours were more prevalent in lakes with TP less than 13 pgL-', while earthy odours were common at higher TP. Drinking water quality issues were reviewed and the relationship between policy, management and science was examined. This work stresses the importance of sound science to ensure the legality, legitimacy, efficiency and effectiveness of implementing water quality policies and for establishing best management practices.

Phytoplankton across the majority of the world’s oceans are thought to be limited by the availability of either nitrate or iron (Fe). However, the spatial resolution of experiments confirming this is low. Two thesis chapters present the results of bottle enrichment experiments at high spatial resolution across (i) the South Subtropical Convergence (SSTC) in the South Atlantic, and (ii) the Scotia Sea-Drake Passage sector of the Southern Ocean. These studies have added detail to the boundaries of limiting nutrients in these regions. Patterns of Fast Repetition Rate fluorometry (FRRf) derived parameters, physiological regulation of these parameters including influences of community structure, and the environmental controls driving them are analysed. Given its role as an essential micronutrient, there has been much effort in constraining potential sources of bioavailable Fe to the ocean, with one such source receiving recent interest: erupted ash from volcanoes. Bottle-scale ash-incubation experiments alongside conventional iron additions and laboratory ash-leaching experiments were conducted, the results of which suggest phytoplankton would respond strongly to ash deposition in the High Nitrate, Low Chlorophyll (HNLC) areas of the Southern Ocean. Particularly notable was the evidence these experiments provided for potential (co-)limitation of phytoplankton in these waters by the micronutrient manganese. The first three chapters of this thesis highlight a number of biogeochemical implications of trace metal stress, particularly that of Fe stress. Therefore, the ability to map the oceanographic extent of Fe-stressed regions using remote sensing would represent a particularly useful advance in marine biogeochemistry. Theoretically it could be possible to map Fe stress from space using satellite images of chlorophyll fluorescence, yet there are important uncertainties that need to be addressed before this can be carried out. In particular, a better understanding of the midday non-photochemical quenching driven reductions in chlorophyll fluorescence occurring at the time satellite images are captured is required. Analysis of over 200 non-photochemical quenching experiments collected over three research cruises, has allowed us to explore non-photochemical quenching and its relevance for using sunlight induced chlorophyll fluorescence to assess broad patterns of Fe stress. Our results have confirmed that satellite fluorescence quantum yields have the potential to reveal broad regions of Fe stress, however a dynamic non-photochemical quenching correction derived from our experiments and analysis was necessary to achieve this.

The effect of environmental conditions upon the growth, production and development of river phytoplankton was investigated for the feeder rivers to the Humber Estuary. The study was part of the Land Ocean Interaction Study LOIS) and focused upon the Rivers Trent and Yorkshire Ouse. The influence of physical, chemical and biological factors upon phytoplankton development were measured through routine fieldwork and laboratory analyses. During fieldwork measurements were collected which complemented measurements collected by LOIS colleagues. Data collected in this study included phytoplankton species composition, density and biomass and is situ rates of growth and production. In situ rates of loss through grazing and respiration were also measured. Laboratory investigations concentrated upon the effects of Ught and temperature upon dominant phytoplankton species and were developed to complement fieldwork. The project focused around four main aims. These were basically to assess the size and composition of phytoplankton maxima in the Trent and Ouse, measure in situ rates of growth and production, estimate losses from grazing and to develop models, using the data collected to assess the effect of environmental conditions upon phytoplankton development and autochthonous carbon in the Humber Estuary. The results showed that phytoplankton dynamics in the Trent and Ouse were controlled primarily by discharge, light and temperature. During spring, when conditions were favourable for growth, rapid phytoplankton growth and maximum rates of production were observed. However, spring floods often interrupted die large phytoplankton populations which developed. Other factors such as grazing and sedimentation were also considered as potentially important in the loss of phytoplankton. The turbid nature of the rivers resulted in a fine balance between photosynflietic gain and respirational loss. This temporal change in environmental conditions resulted in a temporal waxing and waning of the phytoplankton. This in turn had an impact upon the seasonality of the flux of autochthonous carbon to the Humber Estuary. Laboratory investigations and development of a photosynthetic model confirmed the importance of light and temperature upon phytoplankton development in these rivers. In terms of phytoplankton growth and production and the flux of autochthonous carbon, the Trent and Ouse were found to be typical of many other European rivers. The study highlighted the importance of the Trent as a source of autochthonous carbon to the Humber Estuary.

Dissolved organic nitrogen (DON) represents a major pool of fixed, reactive nitrogen in marine systems. It is now recognized that this pool can support primary production and the ability of some algal species to exploit DON compounds as sources of Nitrogen (N) may indicate that specific DON components can exert selective pressure on the composition of the phytoplankton community. In this study the ability of monocultures of ecologically-relevant algal species from the English Channel (Emiliania huxleyi, Micromonas pusilla, Alexandrium minutum and Chaetoceros peruvianus) to grow with DON as the only N source was examined using different artificial media. Among the two tested artificial seawater recipes, Aquil* was preferred as it contained lower micronutrient concentrations, and gave better growth results for all used species. In order to constrain the DON uptake to algae alone, a method for bacterial removal was tested using antibiotic additions. Both Slocombe antibiotic mixture (Cefotaxime-Carbenicillin-Kanamycin-AugmentinTM) and Penicillin-Streptomycin-Neomycin used were effective and not toxic to the algae. Incubation with the antibiotic up to 48 hours and a transfer period into antibiotic-free medium after 72 hours proved to be effective. However, the treatment removed bacteria in A. minutum cultures only; further treatment would be required for the other species to be cultured axenically. The ability to use DON was tested for the above mentioned species using the amino acid L-Arginine (ARG) as the sole N source, and growth was compared with nitrate-containing cultures of the same species. All the selected species grew in both NOᴈ‾ and in ARG, reaching lower final densities when incubated with ARG, although these were not significant. This study has shown that E. huxleyi, A. minutum, M. pusilla and C. peruvianus can grow on organic N, either by direct or indirect uptake, and develop comparable biomasses to species using inorganic N. Both C. peruvianus and M. pusilla cultures contained dissolved ammonium at the end of the experimental period, indicating potential indirect use by the algae of organic N converted to inorganic N by bacteria. A. minutum grew in the presence of ARG along with the cosmopolitan E. huxleyi; N-demand estimates, based on the molar concentration of N-ARG consumed, correlated with the final cell density, indicating that the species did not develop on inorganic N produced from ARG mineralisation, but directly on the ON substrate. Since A. minimum has been linked to harmful algal blooms, and E. huxleyi contributes significantly to oceanic CaCOᴈ deposition, their ability to utilise DON has environmental consequences in addition to the oceanic N-budget. Climate change scenarios predict both episodic conditions of elevated rainfall and extended periods of dry conditions leading to variable riverine inputs to coastal areas, altered nitrogen to phosphorus (N:P) ratios, and changes in the inorganic to organic balance of the nutrient pools. Organic N can constitute up to 69 % of the total N pools, respectively, making it crucial, to understand the cycling of this fraction in coastal waters, and how changes in the composition of nutrient pools could impact on marine ecosystem function and health.

Plankton play a key role in regulating nutrient and carbon cycles in freshwater ecosystems. The uptake and processing of nutrients in planktonic biomass are highly sensitive to changes in the environment, such as alterations in the availability of limiting nutrients, increasing temperature due to climate change, and changes to the composition of interacting species. The focus of this thesis is to use a variety of experimental and theoretical methods to assess and predict the impact of multiple perturbations on community structure, dynamics and ecosystem function, with a particular focus on interactions between phytoplankton and their consumers (zooplankton). Increases in both temperature and phytoplankton species diversity independently decreased CO2 concentrations when the number of non-resource species (those inedible to the zooplankton) were high. Using structural equation modeling I show that the effect is indirect, resulting largely from the positive impacts on total biomass of phytoplankton. Phytoplankton are limited by a range of resources, and differences in the functional traits used to utilize light and nutrients can explain the distributions of species under different temperature regimes. I found that under light and nitrogen limitation, resource requirements are generally lowest at intermediate temperatures, and that changes in temperature may therefore alter the competitive hierarchy amongst species. Using the model freshwater phytoplankton Chlamydomonas reinhardtii, I also find that previous selection environments govern future competitive abilities in phytoplankton. Adaptation to a high salt and low nutrient stress increases competitive ability under light limited conditions, indicating a strong dependency of selection environment for overall competitiveness. This thesis provides a mechanistic insight into the role of diverse plankton communities for community dynamics and ecosystem functioning.

Siu Yuen Yu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 122-139). / Abstracts in English and Chinese. / Abstract (English) --- p.i / Abstract (Chinese) --- p.iii / Acknowledgments --- p.v / Table of Contents --- p.vi / List of Figures --- p.x / List of Tables --- p.xvi / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter CHAPTER 2 --- LITERATURE REVIEW --- p.7 / Chapter 2.1 --- Traditional methods for studying zooplankton feeding selectivity --- p.7 / Chapter 2.1.1 --- Cell counting after laboratory feeding experiments --- p.7 / Chapter 2.1.2 --- Direct examination of gut contents --- p.8 / Chapter 2.1.3 --- Use of radioactive tracers --- p.9 / Chapter 2.1.4 --- Gut fluorescence method --- p.9 / Chapter 2.2 --- High Performance Liquid Chromatography analysis of phytoplankton pigments --- p.11 / Chapter 2.2.1 --- Principle --- p.11 / Chapter 2.2.2 --- Pigments as signature markers of phytoplankton --- p.11 / Chapter 2.2.3 --- Development of HPLC analysis of phytoplankton pigments --- p.16 / Chapter 2.2.4 --- Advantages of HPLC analysis of phytoplankton pigments --- p.17 / Chapter 2.2.5 --- Limitation of HPLC analysis of phytoplankton pigments --- p.18 / Chapter 2.3 --- Zooplankton feeding selectivity --- p.19 / Chapter 2.3.1 --- Ecological importance of zooplankton feeding selectivity --- p.19 / Chapter 2.3.2 --- Factors affecting zooplankton feeding selectivity --- p.19 / Chapter 2.3.3 --- Feeding selectivity of zooplankton studied in this study --- p.21 / Chapter 2.3.3.1 --- p. avirostirs --- p.21 / Chapter 2.3.3.2 --- Paracalanus spp --- p.22 / Chapter 2.3.3.3 --- Pseudevadne tergestina --- p.23 / Chapter 2.4 --- Pigment degradation in guts of zooplankton --- p.24 / Chapter 2.4.1 --- Experimental design --- p.24 / Chapter 2.4.2 --- Pigment degradation --- p.24 / Chapter 2.5 --- "Tolo Harbour, Hong Kong" --- p.26 / Chapter 2.5.1 --- Site description --- p.26 / Chapter 2.5.2 --- Phytoplankton and zooplankton in Tolo Harbour --- p.27 / Chapter CHAPTER 3 --- MATERIALS AND METHODS --- p.28 / Chapter 3.1 --- Field sampling --- p.28 / Chapter 3.1.1 --- Study of seasonal patterns in zooplankton feeding selectivity --- p.28 / Chapter 3.1.1.1 --- Collection of phytoplankton and zooplankton for pigment analysis --- p.28 / Chapter 3.1.1.2 --- Collection of phytoplankton and zooplankton for plankton enumeration --- p.30 / Chapter 3.1.2 --- Collection of phytoplankton and zooplankton for laboratory feeding experiments --- p.32 / Chapter 3.2 --- Laboratory experiments and data analysis --- p.33 / Chapter 3.2.1 --- Study of seasonal patterns in zooplankton feeding selectivity --- p.33 / Chapter 3.2.1.1 --- HPLC of phytoplankton pigments --- p.33 / Chapter 3.2.1.2 --- Fluorometric measurement of chlorophyll-α --- p.35 / Chapter 3.2.1.3 --- Plankton identification and enumeration --- p.36 / Chapter 3.2.2 --- Laboratory feeding experiments for investigation of pigment degradation in zooplankton gut --- p.37 / Chapter CHAPTER 4 --- RESULTS --- p.41 / Chapter 4.1 --- Information on Tolo Harbour --- p.41 / Chapter 4.1.1 --- Temperature and salinity in Tolo Harbour --- p.41 / Chapter 4.1.2 --- Plankton composition and community in Tolo Harbour --- p.43 / Chapter 4.1.2.1 --- Phytoplankton --- p.43 / Chapter 4.1.2.2 --- Zooplankton --- p.50 / Chapter 4.2 --- Seasonal zooplankton feeding selectivity investigated by HPLC phytoplankton pigment analysis --- p.53 / Chapter 4.2.1 --- Verification of HPLC pigment analysis by fluorometric analysis --- p.53 / Chapter 4.2.2 --- Correlations between phytoplankton cell densities and pigment concentrations in water samples --- p.55 / Chapter 4.2.3 --- Feeding selectivity of zooplankton on different phytoplankton groups --- p.73 / Chapter 4.2.4 --- Feeding selectivity of zooplankton on dinoflagellates --- p.87 / Chapter 4.2.5 --- Feeding selectivity of zooplankton on diatoms --- p.87 / Chapter 4.3 --- Feeding selectivity on phytoplankton by other cladoceran - Pseudevadne tergestina --- p.89 / Chapter 4.4 --- Pigment degradation in zooplankton guts after ingestion of phytoplankton --- p.90 / Chapter 4.5 --- Clearance rates of P. avirostris and Paracalanus spp. in feeding experiments --- p.101 / Chapter CHAPTER 5 --- DISCUSSIONS --- p.105 / Chapter 5.1 --- Experiment design --- p.105 / Chapter 5.2 --- Seasonal zooplankton feeding selectivity investigated by HPLC phytoplankton pigment analysis --- p.108 / Chapter 5.2.1 --- Correlations between phytoplankton cell densities and pigment concentrations in water samples --- p.108 / Chapter 5.2.2 --- Feeding selectivity of zooplankton on different phytoplankton groups --- p.108 / Chapter 5.2.3 --- Feeding selectivity of Pseudevadne tergestina --- p.111 / Chapter 5.3 --- Feeding experiments for investigating pigment degradation in guts of zooplankton --- p.112 / Chapter 5.3.1 --- Principle --- p.112 / Chapter 5.3.2 --- Degradation for different pigments in guts of P. avirostris and Paracalanus spp. --- p.112 / Chapter 5.4 --- Clearance rates of P. avirostris and Paracalanus spp. --- p.114 / Chapter 5.4.1 --- p. avirostris --- p.114 / Chapter 5.4.2 --- Paracalanus spp. --- p.115 / Chapter 5.5 --- Limitations of HPLC analysis of phytoplankton pigments --- p.116 / Chapter 5.6 --- Environmental events related to feeding selectivity of zooplankton in Tolo Harbour --- p.118 / Chapter 5.6.1 --- Energy transfer in trophic level --- p.118 / Chapter 5.6.2 --- Abilities of p. avirostris and Paracalanus spp. to control red tides in Tolo Harbour --- p.118 / Chapter CHAPTER 6 --- CONCLUSION --- p.120 / REFERENCES --- p.122 / APPENDIX

Wong Chun Kwan. / "June, 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 211-231). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Marine phytoplankton is responsible for ~50% of global primary productivity, it supports the oceanic food web and affects biogeochemical cycles. I participated in a large mesocosm experiment that observed altered community structure and carbon drawdown in response to increased CO2. There was a 27% reduction in community primary production at the peak of an Emiliania huxleyi-dominated bloom in mesocosms initially at 760 ppm CO2 compared to present day pCO2. There were changes in community structure but not dominance; Synechococcus and large pico-eukaryote abundances were reduced by ~60%, E. huxleyi was reduced by ~50%. A number of E. huxleyi strains persisted throughout the experiment in both treatments and no malformation or significant change in lith size occurred at increased CO2. In a second field experiment in the oligotrophic ocean off the Canary Islands, 760 ppm pCO2 did not change community structure or cell division rates of Synechococcus, Prochlorococcus or pico-eukaryotes.In laboratory experiments, I maintained the diatom, Thalassiosira pseudonana CCMP1335 at 760 ppm and present day pCO2 for ~100 generations in gas equilibrated continuous cultures – one of the longest experiments that has been attempted to investigate the effect of increased CO2 on marine phytoplankton. No clear evidence of adaptation or acclimation to increased CO2 was found, neither were there consistent changes in transcription of RuBisCO or carbonic anhydrase genes. Non-calcified E. huxleyi CCMP1516 and calcified CCMP371 grown in gas equilibrated semi-continuous cultures for several weeks showed no change in cell division rate at 760 ppm CO2. An understanding of the underlying changes in communities is required for modelling responses to increasing CO2, molecular tools may prove useful for this task. The strong community response in the mesocosms shows that rising atmospheric CO2 can greatly affect phytoplankton productivity and biogeochemical cycling.