67 research outputs found
Decoupling Between Bacteria and the Surf-zone Diatom Asterionellopsis glacialis at Cassino Beach, Brazil
No full textThe surf-zone diatom Asterionellopsis glacialis (Castracane) Round attains extremely high abundances (up to 109 cells l–1) and chl a concentrations (up to 1.5 mg chl a l–1), forming darkbrown patches in Cassino Beach, southern Brazil. Several lines of evidence from this study indicate a decoupling between A. glacialis and heterotrophic bacteria. For instance, despite the high abundance of diatoms, associated high levels of chl a and rates of dissolved organic carbon (DOC) production by A. glacialis, bacterial abundance at Cassino Beach was extremely low (0.03 to 0.7 × 106 cells ml–1) compared to the nearby estuarine waters, adjacent coastal waters and those from the literature. No statistical differences were found between bacterial abundance in- and outside the diatom patches, suggesting that direct association with A. glacialis did not stimulate bacterial growth. Moreover, field and laboratory experiments demonstrated that bacteria take 1 to 4 d to begin growing following the input of A. glacialis cell-free filtrate. Five possible reasons for this decoupling, i.e. (1) viral infection, (2) bacterial grazing, (3) DOC quality, (4) nutrient competition and (5) antibiotic production, are discussed. Because of the decoupling between the surf-zone diatom and heterotrophic bacteria in this high-energy surf-zone ecosystem, a large fraction of A. glacialis primary production is not contemporaneously channeled through the microbial food web. Consequently, much of the surf-zone diatom production may fuel metazoan secondary production in the adjacent nearshore and coastal environment.
Copyright Inter-Research 2003, Originally published in Aquatic Microbial Ecology, Vol. 32: 219-228, 2003
Global Significance of the Changing Freshwater Carbon Cycle
No full textFreshwater ecosystems constitute a small fraction of our planet but play a disproportionately large and critical role in the global carbon cycle.</jats:p
From Bacteria to Fish: Ecological Consequences of Seasonal Hypoxia in a Great Lakes Estuary
No full textThe occurrence of bottom-water hypoxia is increasing in bodies of water around the world. Hypoxia is of concern due to the way it negatively impacts lakes and estuaries at the whole ecosystem level. During 2015, we examined the influence of hypoxia on the Muskegon Lake ecosystem by collecting surface- and bottom-water nutrient samples, bacterial abundance counts, benthic fish community information, and performing profiles of chlorophyll and phycocyanin as proxies for phytoplankton and cyanobacterial growth, respectively. Several significant changes occurred in the bottom waters of the Muskegon Lake ecosystem as a result of hypoxia. Lake-wide concentrations of soluble reactive phosphorus (SRP) and total phosphorus increased with decreasing dissolved oxygen (DO). Bacterial abundance was significantly lower when DO was less than 2.2 mg L-1. Whereas there were no drastic changes in surface chlorophyll a concentration through the season, phycocyanin increased threefold during and following a series of major wind-mixing events. Phycocyanin remained elevated for over 1.5 months despite several strong wind events, suggesting that high SRP concentrations in the bottom waters may have mixed into the surface waters, sustaining the bloom. The fish assemblage in the hypolimnion also changed in association with hypoxia. Overall fish abundance, number of species, and maximum length all decreased in catch as a function of bottom DO concentrations. The link between hypoxia and wind events appears to serve as a positive feedback loop by continuing internal loading and cyanobacterial blooms in the lake, while simultaneously eroding habitat quality for benthic fish
Major Contribution from Mesopelagic Plankton to Heterotrophic Metabolism in the Upper Ocean
No full textCarbon, Nitrogen, and Carbohydrate Fluxes during the Production of Particulate and Dissolved Organic Matter by Marine Phytoplankton
No full textPhotochemical Transformations of Surface and Deep Marine Dissolved Organic Matter: Effects on Bacterial Growth
No full textDetrital carbon and nitrogen relations, examined with degrading cellulose
No full textIn the current conceptual framework of aquatic detritus food webs several aspects of carbon and nitrogen dynamics remain still unresolved, in particular the issue of nitrogen enrichment during the course of detritus degradation. Perhaps one of the reasons for this is the use of complex detritus originating from plant sources in most previous studies. Using nitrogen-free pure cellulose as a simple and defined model substrate, we have addressed the detritus nitrogen problem by following the changes in microbial and chemical parameters during its degradation in a semi-continous flow of fresh North Sea water for a period of 12 weeks. Initial colonization and growth of heterotrophic bacteria and associated mucus was followed by heterotrophic protozoa. Closely attached or loosely bound cells that were embedded in voluminous mucus constituted the bacterial community. Protozoa comprised heterotrophic nanoflagellates, and large euglenoid flagellates. The euglenoids produced plentiful faecal pellets 3 to 4 micrometer in diameter; a novel source of microscopic detrital particles. By about 12 weeksŽ time, patches of cellulose fibres had been totally converted to microbial biomass and associated mucus. The carbon content decreased from 40% to 25% of the initial cellulose weight, while nitrogen increased from 0% to 0.5% as a result of net uptake of dissolved nitrogen from the ambient water. Elutriation experiments with dilute acetic acid showed that, after 12 weeks, 4.2 % of the total nitrogen in degrading cellulose was present as amino acids presumably weakly bound in some way to the mucus secreted by microorganisms, indicating a potential for sequestering capability of microbial slime that is ubiquitous in the aquatic environment. Results suggest that degrading detritus may gain an increasing pool of labile nitrogen compounds other than microbial protein which may be of considerable importance for animal nutrition
Abundance, Size Distribution, and Stable Carbon and Nitrogen Isotopic Compositions of Marine Organic Matter Isolated by Tangential-Flow Ultrafiltration
No full textDiscerning the role of denitrification, anammox, and N2O production in aquatic systems
No full text"This dissertation investigates (1) the magnitude and relative importance of denitrification and anammox in aquatic nitrogen (N) loss, (2) microbial pathways of nitrous oxide (N2O) production, (3) impact of ecosystem restoration on N loss and export, and (4) linkages of N loss with harmful algal blooms (HABs). Study ecosystems included a mesotrophic lake, a wetland undergoing restoration, an embayment of Lake Erie, and a coastal seagrass bed. A variety of stable isotopic techniques were employed to achieve these research objectives." -- Abstract.(Ph. D.)--Michigan State University. Integrative Biology, 2017Includes bibliographical reference
Cold and wet: diatoms dominate the phytoplankton community during a year of anomalous weather in a Great Lakes estuary
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