Degradation of water quality, introduction of dreissenid mussels (notably <i>Dreissena polymorpha</i>) and depletion of oxygen concentrations in the hypolimnion in Lake Simcoe, Ontario prompted a study of phytoplankton primary production to inform efforts to improve the lake conditions. The characterization of algal production is critical since, as primary producers, their biomass is positively correlated with production at higher trophic levels in pelagic food webs and oxygen levels. This study was conducted from August 2010 to August 2011, including the winter season (Dec-Mar). Temporally, the lake displayed a unimodal pattern with late summer to fall production maxima. For all seasons considered, the pelagic daily areal primary production (P_int) was lower in the nearshore than offshore, consistent with the nearshore shunt hypothesis that mussels should be able to deplete phytoplankton more effectively in the nearshore. The sensitivity analysis revealed that chl a and the photosynthetic parameter P^B_max were the most influential variables for explaining such spatial differences. The size distribution of chl a and production varied where both netplankton (>20µm) and nanoplankton (2-20µm) were greatest in fall and picoplankton (<2µm) was highest in summer and early fall. A large chl a peak of nanoplankton was also found in late-winter (Mar) at offshore stations. The seasonal areal primary production (SAPP; May-Oct) and chl a:TP were significantly lower nearshore than offshore, consistent with grazing impacts from the large nearshore dreissenid mussel community. The lake as a whole is quite productive comparable to other large lakes with comparable total P concentrations and dreissenid mussel populations. The latter part of the study showed that the deep chlorophyll layer (DCL) was not as frequent as expected and was detected only 28% of time during late-spring to summer when the lake was thermally stratified (Aug-Sept 2010 and May-Aug 2011). The percent dissolved oxygen (%) did not show any indications of elevated primary production in the DCL although the production estimates suggested that there is a substantial (an average of 55%) amount of primary production occurring below thermocline when a DCL exists. Whether or not the DCL has potential to nourish the benthic filterers (dreissenids) and has ecological significance in the lake remains unclear. Overall, the factors that control phytoplankton primary production in Lake Simcoe seem to operate somewhat differently from other large lakes and further investigation is needed to elucidate them. The analysis of primary production and biomass has improved knowledge of non-summer production and can provide guidance to site-specific P and oxygen remediation.

University of Macau / Institute of Chinese Medical Sciences

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 234-254). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 234-254). Also available on the Internet.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 25, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Anand Chandrasekhar. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes bibliographical references (p. 153-165).

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 187-198). Also available in electronic version. Access restricted to campus users.

Foodborne toxins include a variety of biologically produced toxins and process-induced toxicants. Among them, marine algal toxins in polluted seafood can induce serious harmful effects on human, while heat-induced toxicants remain in a wide range of food and chronically affect health. In this present study, several representative toxins from these two categories were selected and studied, they are, brevetoxins (PbTxs), saxitoxin (STX) and acrolein (ACR). During past decades, the molecular actions of these toxins have been well studied, however, their effects and mechanisms corresponding to their sublethal toxicity in vivo still need more investigation. Therefore, in our current study, we adopted medaka fish (Oryzias melastigma) and zebrafish (Danio rerio) as models to study the toxicological responses and pathways of these selected toxins at the molecular and cellular level. In the first part of study, the targeted organs of medaka fish, gills and brains, were studied in medaka fish after exposure to the sublethal level of PbTx-1, the most potent neurotic shellfish poisoning (NSP) toxin. Facilitated by the two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ ionization tandem time-of-flight mass spectrometry (MALDI TOF/TOF MS), proteins affected by PbTx-1 in these organs were identified, including myosin like proteins, aldose reductase, gelsolin and keratin. Collectively, the proteins altered after exposure suggested the altered calcium ion binding process, and dysfunction in cytoskeleton assembly and metabolism. After successfully applying the fish model and proteomic approaches in the NSP toxin study, we put emphasis on the developmental toxicity of foodborne toxins, as children are more sensitive and vulnerable to foodborne toxins. Among the marine algal toxins, paralytic shellfish poisoning (PSP) toxins are the commonest and most lethal ones with STX as the most potent PSP toxin. Therefore, we examined the developmental effects of STX using medaka model. By exposing medaka embryos from the early blastula stage onwards, which covered the main developmental stage of the central nervous system and somites, we found newly hatched medaka fish exhibit abnormal growth with longer body length and relatively smaller yolk sac size. High cell proliferation, neuron development, and metabolism were confirmed by whole-mount immunostaining and 2-DE. In summary, STX disturbs the normal growth of medaka embryos probably by affecting the metabolic rate in the exposed medaka embryos. Opposite to STX, after exposure to ACR, a pollutant that ubiquitously exists in food and environment, the zebrafish exhibited delayed development. ACR is a known glutathione (GSH) depleting factor and oxidative stress inducer. Apart from developmental retardance, increased reactive oxygen species (ROS) and inflammation were found in newly hatched zebrafish, suggesting the developmental delay may be partly related to the ACR-induced oxidative stress. In summary, findings from the present study highlighted the molecular responses and possible pathways of some selected foodborne toxins. Developmental effects and toxicity were also found after exposing to both the biologically produced toxin and the heat-produced toxicant. Our current study makes contributions to the knowledge on the hazardous effects of foodborne toxins in vivo, and provides useful information for the further study on the human health. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

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