Gonyostomum semen is a raphidophyte microalgae that can be found in brown water lakes all over Sweden. The species forms substantial summer blooms that can completely dominate the phytoplankton community, largely due to its limited grazing pressure. To test whether parasites control the abundance of G. semen, as well as to study a newly discovered predator – prey interaction, three experiments were set up. The first experiment aimed to look at potential parasite interactions by screening for infections in natural environments, but none could be found. The second experiment built on the first by testing if the lack of parasites was due to physiological characteristics of G. semen, by exposing the species to diatom parasites and observing the cell’s response. The third experiment investigated the impact of a predatory ciliate on G. semen cell abundance. This predator – prey interaction was first observed in fresh lake water samples and had so far not been described in the literature. First, G. semen alone was exposed to the ciliate, and later the prey preference of the ciliate was examined by offering it four different potential prey species. The results from the first and second experiment suggested that G. semen does not have any parasites, potentially due to lack of a supportive cell wall. When interacting with parasite zoospores, the G. semen cells burst open, meaning that a successful infection would not be possible. The third experiment showed that the ciliate does feed on G. semen, and that it likely prefers G. semen over other types of prey. The limited top – down control on G. semen gives the species an ecological advantage and is seemingly one of the main reasons for G. semen’s success in spreading to new habitats.

Fluorescence (F), DCMU-enhanced fluorescence (F^DCMU) and a ratio of these two measurements (F ratio) were found to be useful indicators of light history but not physiological condition of natural phytoplankton assemblages. Changes in the fluorescence properties of unialgal continuous and batch cultures at different growth rates and following nutrient addition were observed only during nutrient starvation. Nutrient deficiency in Lake Ontario was not revealed either by seasonal patterns of fluorescence or by short term changes in the F ratio following nutrient additions. This result however is not conclusive evidence of nutrient sufficiency because of the insensitivity of the fluorescence ratio as an indicator of growth rate. The depression of F and F^DCMU observed in surface waters of Lake Ontario occurred during conditions of high light and low mixing rates. The result suggests that ''photoinhibition" of photosynthesis as measured by conventional primary productivity techniques, may occur in nature only under these particular conditions. A general relationship between temperature gradients or water column stability and the difference in fluorescence between 1 and 10 meters was observed. This relationship was due to both vertical structure in the assemblage and the physiological effect of light on fluorescence. Diurnal patterns of fluorescence were found to be due to the physiological effect of light on fluorescence rather than a circadian rhythm. The physiological effect was dependent on both the duration and intensity of exposure of the cells to light as well as the sensitivity of the assemblage to light. Differences were associated with seasonal changes in species composition with spring and winter populations exhibiting the greatest sensitivity. / Thesis / Master of Science (MSc)

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1982. / Microfiche copy available in Archives and Science / Vita. / Includes bibliographies. / by Daniel James Repeta. / Ph.D.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Bibliography: leaves 138-143. / by William Sunda. / Ph.D.

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

Production dynamics in the phytoplankton community of a mesotrophic Texas reservoir were measured weekly over a four month period using 14C incubation and ATP assay methodologies. Assimilation values of 14C ranged from 0.2 to 45 ug C 1 hr1 - . Significant positive and occasionally negative changes in biomass (i.e. viable organic carbon) were observed in short term (4 hr) in situ incubations juxtapo-sitioned with the 14C experiments; viable organic carbon production, estimated with the ATP assay, ranged from -25 to +50 ug C 1l1hr1. Carbon assimilation and biomass changes did not correlate in either short term (4-5 hr.) or over the study period (6 months). However, weekly biomass trends were predicted by relative positive or negative biomass changes in the short term incubations. Biomass measurements gave a more sensitive insight into production dynamics in the phytoplankton community than did carbon assimilation measurements.

Chan Lai-chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1991. / Bibliography : leaves 139-154. / List of Tables --- p.V / List of Figures --- p.VI / Acknowledgements --- p.XIV / Abstract --- p.1 / Chapter Chapter 1 --- General introduction --- p.4 / Chapter Chapter 2 --- Literature review / Chapter 2.1. --- The Tolo Harbour Water Control Zone --- p.8 / Chapter 2.2. --- Hydrography of Tolo Harbour --- p.11 / Chapter 2.2.1. --- Temperature --- p.12 / Chapter 2.2.2. --- Salinity --- p.13 / Chapter 2.2.3. --- Secchi depth --- p.14 / Chapter 2.2.4. --- Dissolved oxygen --- p.15 / Chapter 2.3. --- Eutrophication in Tolo Harbour --- p.16 / Chapter 2.3.1. --- Nutrients --- p.17 / Chapter 2.3.2. --- Chlorophylls --- p.20 / Chapter 2.3.3. --- Red Tides --- p.21 / Chapter 2.4. --- Marine plankton in Tolo Harbour --- p.24 / Chapter 2.4.1. --- Phytoplankton --- p.24 / Chapter 2.4.2. --- Zooplankton --- p.25 / Chapter Chapter 3 --- The hydrography and marine plankton of Tolo Harbour / Chapter 3.1. --- Introduction --- p.27 / Chapter 3.2. --- Materials and Methods --- p.30 / Chapter 3.3. --- Results --- p.33 / Chapter 3.4. --- Discussion --- p.50 / Chapter Chapter 4 --- Seasonal dynamics of crustacean zooplankton in Tolo Harbour / Chapter 4.1. --- Introduction --- p.57 / Chapter 4.2. --- Materials and Methods --- p.58 / Chapter 4.3. --- Results --- p.59 / Chapter 4.4. --- Discussion --- p.71 / Chapter 5 Biology of the marine cladoceran Penilia avirostris Dana in Tolo Harbour / Chapter 5.1. --- Introduction --- p.77 / Chapter 5.2. --- Materials and Methods --- p.79 / Chapter 5.3. --- Results --- p.81 / Chapter 5.4. --- Discussion --- p.92 / Chapter Chapter 6 --- Grazing behaviour of the marine cladoceran Penilia avirostris Dana in Tolo Harbour / Chapter 6.1. --- Introduction --- p.97 / Chapter 6.2. --- Materials and Methods --- p.99 / Chapter 6.2.1. --- Isolation of algae from Tolo Harbour --- p.99 / Chapter 6.2.2. --- Algal culture --- p.99 / Chapter 6.2.3. --- Measurement of gut content --- p.100 / Chapter 6.2.4. --- Measurement of gut evacuation rate --- p.101 / Chapter 6.2.5. --- Measurement of ingestion rate and clearance rate --- p.102 / Chapter 6.2.6. --- Feeding impact --- p.103 / Chapter 6.2.7. --- Laboratory feeding experiments --- p.103 / Chapter 6.2.8. --- In situ experiment --- p.104 / Chapter 6.3. --- Results --- p.107 / Chapter 6.3.1. --- Indoor experiment --- p.107 / Chapter 6.3.2. --- In situ study --- p.120 / Chapter 6.4. --- Discussion --- p.129 / Chapter Chapter 7 --- General conclusion --- p.135 / References --- p.139

An analysis and correlation of phytoplankton communities with physicochemical data from 3 sites in Lake Texoma was conducted to supplement time-series data. Water and phytoplankton were sampled monthly, March, 1976-February, 1977. Simple correlations were run between all physicochemical parameters and phytoplankton standing crop from the 3 sites. Multiple linear regression analyses were used to develop equations predictive of phytoplankton standing crop and chloride concentration. Minerals leached from marine sediments in the Red River chennel contribute to formation of a, halocline which seals the anoxic hypolimnion from the reservoir surface in midsummer. Conductivity decreased west to east, 2980-1800. pmhos/cm. Maximum mean annual phytoplankton standing crop in Red River arm was 36 percent greater than midlake. Eutrophication was evident.

Lie, An Ying Alice. / Thesis submitted in: November 2008. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 115-134). / Abstracts in English and Chinese. / Chapter Chapter 1. --- Introduction --- p.1 / Chapter 1.1. --- Microzooplankton --- p.1 / Chapter 1.1.2. --- Microzooplankton grazing --- p.1 / Chapter 1.2. --- Dilution method --- p.4 / Chapter 1.2.1. --- Basic principles --- p.4 / Chapter 1.2.2 --- Variation and extensive uses of the dilution method --- p.7 / Chapter 1.2.3. --- Criticism of the dilution method --- p.9 / Chapter 1.2.4. --- Results of the dilution experiments and their implications --- p.11 / Chapter 1.3. --- The roles of microzooplankton --- p.16 / Chapter 1.4. --- Phytoplankton --- p.18 / Chapter 1.4.1. --- Size classification --- p.18 / Chapter 1.4.2. --- Chemotaxonomic marker pigments --- p.19 / Chapter 1.4.3. --- Nutrients and phytoplankton dynamics --- p.19 / Chapter 1.5. --- Hypothesis --- p.26 / Chapter 1.6. --- Objectives --- p.26 / Chapter 1.7 --- Research outline --- p.27 / Chapter 1.7.1. --- Microzooplankton grazing rates and phytoplankton growth rates --- p.27 / Chapter 1.7.2. --- Phytoplankton group selection --- p.27 / Chapter 1.7.3. --- Phytoplankton size selection --- p.27 / Chapter 1.8. --- Study sites --- p.27 / Chapter 1.81. --- Tolo Harbour --- p.28 / Chapter 1.8.2. --- Mirs Bay --- p.28 / Chapter 1.8.3. --- Biological and physio-chemical parameters --- p.30 / Chapter Chapter 2. --- Materials and methods --- p.33 / Chapter 2.1. --- Study site and sampling --- p.33 / Chapter 2.2. --- Dilution experiments --- p.33 / Chapter 2.2.1. --- Preliminary dilution experiments and enrichment tests --- p.35 / Chapter 2.2.2. --- HPLC --- p.37 / Chapter 2.2.3. --- Pigment data analysis --- p.41 / Chapter 2.2.4. --- Phytoplankton and microzooplankton community analysis --- p.42 / Chapter Chapter 3. --- Results --- p.43 / Chapter 3.1. --- Field parameters --- p.43 / Chapter 3.1.1. --- Physiochemical parameters --- p.43 / Chapter 3.1.2. --- Chlorophyll a --- p.46 / Chapter 3.2. --- Initial conditions --- p.49 / Chapter 3.2.1. --- Phytoplankton pigment and size fraction composition --- p.49 / Chapter 3.2.2. --- Microscopy cell counts --- p.56 / Chapter 3.3. --- Dilution experiments results --- p.64 / Chapter 3.3.1. --- Linear regression analysis results --- p.64 / Chapter 3.3.2. --- Estimated pigment specific phytoplankton growth rates and microzooplankton grazing rates --- p.66 / Chapter 3.3.3. --- Ratio of microzooplankton grazing to the phytoplankton growth rate in ambient nutrient --- p.70 / Chapter 3.4. --- Correlation analyses --- p.78 / Chapter 3.4.1. --- Physiochemical parameters --- p.78 / Chapter 3.4.2. --- Initial pigment concentration --- p.81 / Chapter 3.4.3. --- Initial densities --- p.81 / Chapter 3.4.4. --- Phytoplankton growth rates and microzooplankton grazing rates --- p.82 / Chapter 3.5. --- Percentage and composition shifts --- p.83 / Chapter 3.5.1. --- Percentage change --- p.83 / Chapter 3.5.2. --- Size fraction --- p.83 / Chapter 3.5.3. --- Pigment markers --- p.83 / Chapter Chapter 4. --- Discussions --- p.103 / Chapter 4.1. --- Hypothesis --- p.103 / Chapter 4.2. --- Phytoplankton growth rates and microzooplankton grazing rates --- p.104 / Chapter 4.3. --- Dilution experiment --- p.105 / Chapter 4.3.1. --- Nutrient enrichment --- p.105 / Chapter 4.3.2. --- Shift of pigment compositions --- p.106 / Chapter 4.3.3. --- Experiment limitations --- p.107 / Chapter 4.4. --- Microzooplankton feeding preference --- p.108 / Chapter 4.4.1. --- Phytoplankton size --- p.108 / Chapter 4.4.2. --- Phytoplankton group --- p.109 / Chapter 4.5. --- Food web dynamics --- p.110 / Chapter 4.5.1. --- The role of microzooplankton --- p.110 / Chapter 4.5.1.1. --- Nutrient recycling --- p.110 / Chapter 4.5.1.2. --- Energy transfer --- p.111 / Chapter 4.5.1.3. --- Phytoplankton control --- p.111 / Chapter 4.5.2. --- The role of mesozooplankton --- p.111 / Chapter Chapter 5. --- Conclusions --- p.113 / References --- p.115 / Appendices --- p.135

The influence of mesoscale ocean eddies on near-surface ocean temperature, surface stress and phytoplankton communities is investigated by collocating numerous satellite measurements along with vertical profiles of oceanic temperature and salinity to the interiors of eddies identified and tracked in altimetric sea surface height maps. The surface currents associated with mesoscale ocean eddies impart a curl of the surface stress from the relative motion between surface air and water. This stress curl has a polarity opposite that of the vorticity of the eddy, thus attenuating the eddies by generating Ekman upwelling in the cores of anticyclones and downwelling in the cores of cyclones. Ekman pumping also arises from eddy-induced spatial variability of the sea surface temperature (SST) field that generates a wind stress curl in regions of crosswind SST gradients through a response of surface winds to SST-induced surface heating variations. SST-induced Ekman pumping is shown to be secondary to surface current-induced pumping in most regions of the World Ocean. Eddy-induced Ekman pumping resulting from the combination of surface current effects and air-sea interaction represents an order 1 perturbation of the background, basin-scale Ekman pumping velocities from the large-scale wind fields. In western boundary currents and equatorward-flowing eastern boundary currents, cyclonic eddies preferentially entrain water from the coastal side of the boundary current, which primes the interiors of cyclones to have phytoplankton concentrations that are elevated relative to the background. In contrast, anticyclones formed in these regions contain locally depressed phytoplankton concentrations from the offshore waters. While eddy pumping from vertical displacements of isopycnals during eddy formation can affect the biology in the interiors of cyclones during the transient stage of their development, this ecosystem response cannot be sustained because of the persistent eddy-induced Ekman downwelling throughout the rest of the eddy lifetimes. Likewise, the persistent eddy-induced Ekman upwelling in anticyclones is of little benefit because of their low phytoplankton content at the time of formation. A definitive response to eddy pumping is therefore difficult to detect from satellite observations alone. Eddies formed in regions where anticyclones preferentially entrain water with elevated phytoplankton concentrations, such as the South Indian Ocean, or in some mid-ocean gyre regions where small-amplitude eddies form (e.g., the oligotrophic South Pacific), an ecosystem response to eddy-induced Ekman pumping is observed. Conversely, cyclones in these regions entrain water that is low in chlorophyll, resulting in negative chlorophyll anomalies that are sustained by Ekman downwelling throughout the eddy lifetimes. The phytoplankton response to eddy-induced Ekman upwelling in anticyclones is seasonal, occurring only during the winter. It is proposed that the mechanism for the lack of ecosystem response to eddy-induced Ekman upwelling during the summer is the decoupling of the mixed layer from the nutricline. The observations presented in this dissertation provide a baseline from which coupled ocean circulation and biogeochemical models can be assessed. If coupled models are able to reproduce correctly the observed influence of mesoscale eddies on photoautotrophic communities, further insight into the mechanisms for this variability could be gained from the model output using the methodologies developed in this dissertation together with investigation of subsurface variability in the models below the depth to which chlorophyll can be inferred from the satellite observations. / Graduation date: 2013