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The goal of this study was to determine the significance of dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON) to harmful phytoplankton. Two regions that experience frequent and persistent harmful algal blooms (HABs) were examined, the Eastern Gulf of Mexico and York River, Virginia. Nitrogen uptake by harmful algae in these regions was examined using a combination of stable isotopic (15N) tracer techniques and nutrient bioassays. In the Eastern Gulf of Mexico, kinetic parameters for uptake of N substrates by K. brevis were determined and indicated the greatest preference for ammonium (NH4+), although all substrates tested were taken up. Investigation of N uptake by K. brevis in the light and dark revealed periodicity of diet uptake rates with the maximum and minimum rates measured early in the light and dark periods, respectively. The highest rates of uptake were observed for NH4+. Ratios of NH4+ regeneration:uptake were ∼1, indicating the importance of regeneration processes to blooms. Three strains of K. brevis exhibited significant differences in N uptake rates. The observed nutritional flexibility of K. brevis likely helps it flourish under a range of conditions spanning bloom initiation in oligotrophic offshore waters to bloom maintenance inshore. In the York River, N uptake was dominated by NH4+ with the highest uptake rates at all stations, for all size fractions and for all seasons, ranging from 34 to 80% of total absolute uptake. Rates of N uptake by A. monilatum are the first reported for this species in the York River, and demonstrate uptake of a diverse suite N substrates. During the A. monilatum bloom NH4+ regeneration rates equaled those of uptake, indicating the importance of regeneration to blooms. Additionally, three anthropogenic N sources were used to assess their role in exacerbation of a HAB during a 7 day bioassay. Urban parking lot run-off (+ Urban), soil from a construction site (+ Soil) and paper mill run-off (+ Industrial) were added to a natural bloom assemblage. Results indicated the anthropogenic sources had unique N compositions; DIN comprised ∼9%, 91% and 20% of + Urban, + Soil, and + Industrial, respectively. All N sources stimulated the growth of phytoplankton with the + Urban and + Soil treatments eliciting the greatest response, a doubling in Chl a and/or cell concentrations along with nutrient drawdown of both DIN and DON within two days. The results of this dissertation emphasize the importance of a flexible metabolism to the success of the HAB species investigated here. All harmful phytoplankton studied were able to utilize the variety of DIN and DON sources supplied. Additionally, a universal preference for NH4+ was observed in all studies despite the distinct regions examined and unique characteristics of each species.

The effects of chlorinated sea water on the blue crab, Callinectes sapidus Rathbun, were evaluated through measurements of acute toxicity, serum constituents (protein, total ninhydrin positive substances, chloride, osmotic, sodium, potassium, calcium, and magnesium concentrations), oxygen consumption and ventilation rates in whole crabs, and oxygen consumption of excised gills. Histological examination of gills was also performed. The 96-hr LC50 for female blue crabs exposed to chlorinated sea water at 21�C and 14('0)/00 was 0.86 mgCl(,2)/l CIO (chlorine induced oxidants). The value for males under similar conditions was 0.84 mgCl(,2)/l CIO. Mortality was uncommon below 0.61 mgCl(,2)/l, but reached 100% with as little as 1.15 mgCl(,2)/l. Exposure of adult females to 0.79 mgCl(,2)/l CIO for two hours in a flow-through respirometer caused decreases in oxygen consumption. These decreases were interpreted as short-term reactions to sensing the chlorinated water, since 96-hr exposures of crabs to 0.99 MgCl(,2)/l CIO caused no consistent changes in statistically measured oxygen consumption of whole crabs or excised gills relative to controls. In addition, except for short-term reactions, the same levels of CIO had no effects on crab ventilation rates. Histological examination of gills revealed no observable damage from exposure to CIO. CIO levels ranging from 0.36 to 1.04 mgCl(,2)/l had no consistent effects on any of the serum constituents, except for magnesium. Hyporegulation of this ion was disrupted (serum magnesium concentration increased relative to controls and approached external medium levels) during 96-hr exposures of crabs to CIO levels of 0.47 mgCl(,2)l and higher. The magnitude of the effect was directly related to dose. The effect of CIO on blue crab serum magnesium is the same as that found for other crabs exposed to CIO and chlorinated hydrocarbon pesticides. It is hypothesized that increased serum magnesium levels interfere with neural activity, causing death. Since magnesium regulation in the blue crab occurs at the bladder wall, the implication is that CIO acts on the crab at this internal site. This possibility compounds the already difficult problem of toxicant identification when using CIO.

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Southern Ocean waters have been identified as critical regions because of their potential to impact global climate as they play an integral role in oceanic overturning and circulation. They are also an area of deep and intermediate water formation and can potentially modulate atmospheric CO 2 concentrations. This project focuses on two regions that are seasonally limited by biologically available iron, the open HNLC Southern Ocean and the Ross Sea. The objective of this project was to determine how iron impacts the regulation of photosystem II and how the presence of particular phytoplankton species affects the ability of satellites to estimate biomass from remote sensing of ocean color. Two pulse amplitude modulated fluorometers were used to examine the photochemical efficiency of whole phytoplankton assemblages and single cells in both iron enrichment experiments and during a natural phytoplankton bloom in the Ross Sea from 2001--04. There were no significant differences in the photochemical recoveries of diatoms during the Southern Ocean Iron Experiment, with exception of Asteromphalus sp. (a centric diatom). The kinetics of increase from iron stress suggested that they occurred independently of cell surface area. A relationship between diatom abundance and SeaWiFS overestimation of chlorophyll a in the eastern Ross Sea was found in 2001--2, but this trend was not observed in other years when diatoms dominated. Under most circumstances (phytoplankton composition and size distribution), it appears that with a linear post-calibration correction we could utilize SeaWiFS for phytoplankton biomass estimates in the Ross Sea. However, we could not explain the degree that SeaWiFS over- or underestimated the in situ chlorophyll a with taxonomic composition or phytoplankton size distribution. There was distinct interannual variability in the Ross Sea over the course of our three year study. In February 2003 there was a clear secondary bloom dominated by diatoms, a feature previously unreported in the central Ross Sea. Intrusions of modified circumpolar deep water regulated the timing and magnitude of the second diatom bloom in 2003--2004 by infusing surface waters with additional iron. We could not conclusively explain the spatial variability in the phytoplankton assemblage with the fluorescence-based light utilization parameters or the mixed layer depth.

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