| 1. Fate of recently fixed N2 in the eastern Gulf of Mexico: Does the regeneration of N by Trichodesmium support the development of Gymnodinium breve blooms?
Funded by the National Science Foundation , Biological Oceanography
Co-PIs: Cynthia Heil at the University of South Florida
Debbie Bronk at the Virginia Institute of Marine Sciences
Blooms of the toxic red tide dinoflagellate, Karenia brevis (formerly Gymnodiniumbreve), are an important feature of the Florida Shelf ecosystem. It has been hypothesized that blooms initiate and develop in an oligotrophic, mid-shelf region 18-75 km offshore of west Florida. However, these waters are characterized by low concentrations of both dissolved inorganic and organic nitrogen (DIN and DON), and so it is unclear how K. brevis blooms meet their N demand for growth. Ambient N concentrations, model predictions, and stoichiometric calculations of nutrient requirements for growth based on observed biomass suggest that N inputs from riverine, upwelling and in situ N regeneration are insufficient to support the observed K. brevis blooms in this region. Furthermore, unpublished research, anecdotal information and historical red tide monitoring data suggest a correlation between the timing and magnitude of K. brevis blooms and the occurrence of the filamentous, N2 fixing cyanobacteria, Trichodesmium spp. in both the Gulf of Mexico and Atlantic coastal waters.
Although it is now known that Trichodesmium occur and fix N2 throughout the tropical and subtropical oligotrophic oceans, little is known about the fate and significance of new N inputs derived from recently fixed N 2 or of the pathways of trophic transfer whereby this new N is assimilated into oligotrophic marine ecosystems. It is critical that we determine the fate of new N in oligotrophic systems and the effects of N inputs from N2 fixation on the community structure and function so that we can accurately assess the impact of new N on regenerated and export production.
We hypothesize that that blooms of K. brevis in west Florida shelf waters are supported by the release and regeneration of DIN and DON from N2 recently fixed by co-occurring or preceding blooms of Trichodesmium spp. The oligotrophic, west Florida Shelf ecosystem is characterized by large blooms of both Trichodesmium and K. brevis, and so is an ideal model system in which to examine the fate of new N inputs from N2 fixation by Trichodesmium spp. and the pathways facilitating the trophic transfer of this N to dinoflagellates.
We are embarked on a three-year program during which we are conducting:
- Laboratory and field studies to determine the capacity for and kinetics of N regeneration by Trichodesmium and uptake by K. brevis using stable isotopes.
- Laboratory and field studies to identify associated communities and examine trophic pathways whereby newly fixed N2 derived from Trichodesmium spp. stimulates production in otherwise oligotrophic waters.
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Results and Links
2. Nutritional factors promoting the growth and dominance of Aureococcus anophagefferens in coastal waterways.
Funded by the National Oceanographic and Atmospheric Administration/Coastal Ocean Program - ECOHAB Program
More information about ECOHAB
Co-PI: Liz Minor at ODU
Dissolved organic material (DOM) has been implicated as a causative agent promoting the growth of harmful algal species and initiating blooms in the inland waterways of the Eastern United States. In particular, the brown tide pelagophyte, Aureococcus anophagefferens , occurs at bloom densities in the inland waterways of RI, NY, NJ, DE and MD. It is likely that its geographical range extends into VA. These areas tend to be shallow and have restricted flushing and therefore are impacted by nutrient inputs from in situ recycling processes, terrestrial runoff, groundwater inputs and sediment resuspension.
We are embarked on a two-year project to: determine the nutrient conditions that promote brown tides, identify compounds and compound classes that stimulate the growth of A. anophagefferens , determine possible sources of DOM and its importance to the nutrition of this species, and assess how competition for DOM and nutrients affects growth of A. anophagefferens relative to co-occurring taxa.
To meet our project goals, we have selected field sites that have similar physical attributes (e.g., circulation and morphology) but different densities of A. anophagefferens. Sites selected are in Chincoteague Bay, where A. anophagefferens is known to occur at high densities, and at more southerly sites that are less urbanized, have different sources of DOM and have not previously experienced high abundances of this species (e.g., Hog Island Bay), but may be vulnerable to blooms if there are changes in nutrient conditions. Studies are being based out of the Marine Consortium's Laboratory in Greenbackville, VA ( http://www.msconsortium.org/ ) and the Virginia Institute of Marine Science's Eastern Shore Laboratory (ESL) in Wachapreague, VA ( http://www.vims.edu/bio/easternshore.html).
We are employing a variety of new, state-of-the art techniques to characterize DOM, identify and measure the primary pathways of C and N cycling and determine the competitive interactions that affect the cycling of DOM and its use by mixotrophs, such as A. anophagefferens . This work will answer basic questions regarding the extent to which organic N and C supports the growth of A. anophagefferens , the nutrient conditions that stimulate blooms and mixotrophy, how competition for DOM varies depending on its source and composition, and differences among areas that experience blooms and those that do not.
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Results and Links
3. Harmful algal blooms in Virginia's estuaries: Nutritional factors promoting bloom formation.
Funded by the Virginia Environmental Endowment
Harmful algal blooms appear to be increasing in their geographical extent and frequency and have resulted in severe economic and public health impacts around the world, including the United States and Virginia. Harmful species can elicit adverse effects either directly, by the production of potent toxins that kill or harm fish (or people), or indirectly, through the production of excessive biomass and eutrophication. Effects of excessive production of algal biomass include: shading of submerged vegetation, disruption of food web dynamics and structure, and oxygen depletion as blooms decay. Species that form HAB's represent a variety of taxa that occur naturally in the environment and may "bloom" when environmental conditions are altered to give them a competitive advantage over other co-occurring taxa.
The late spring/early summer plankton communities of the Chesapeake Bay and the Virginia coastal waterways contain a number of potentially harmful algal bloom species (e.g., Pfiesteria piscicida, Prorocentrum minimum, Gyrodinium galatheanum, Katodinium rotundatum, Cochlodinium heterolobatum, Gymnodinium spp. (link to Gymnodinium bloom slide), and Aureococcus anophagefferens ) that can reach bloom densities and result in the damage or loss of seagrass beds and finfish and shellfish resources. Increases in the occurrence of HAB's, including those species that occur in the lower Chesapeake Bay, have been attributed to changes in water quality in a variety of locations; specifically, the enrichment of estuarine waters with dissolved organic material (DOM) relative to inorganic nutrients. Elevated DOM concentrations can result from direct inputs of organic wastes, such as runoff from animal farms or human waste from septic fields and/or inefficient sewage treatment, or indirectly, as a result of nutrient recycling.
This three-year will investigate the role of nutrients and organic material in the formation of algal blooms in the lower Chesapeake Bay. Negative economic and environmental impacts due to harmful algal blooms have already been reported in Virginia's estuarine waters. Because blooms are already occurring and may increase either directly or indirectly as a result of inputs of organic or inorganic nutrients or through recycling processes, it is important to identify and understand the nutritional factors promoting blooms. It is crucial that we understand the processes and pathways through which nutrients become available to these organisms so that we can: (1) mitigate the effects of blooms that result from natural or cultural eutrophication of water bodies, and (2) prevent their appearance in locations that have not previously experienced blooms or their economic and environmental repercussions.
This research will help elucidate some of the common causes of algal blooms. As a result of these studies, we may be better able to predict how the timing and magnitude of organic and inorganic nutrient enrichments affects the growth of populations and thereby mitigate the effects of nutrient discharges using best management practices.
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Results and Links
4. Factors Influencing the Rates and Mechanisms of Phytoplankton-Mediated Hydrogen Sulfide Production in Contrasting Oceanic Regimes
Funded by the National Science Foundation, Chemical Oceanography
Co-PI: Greg Cutter at ODU
Hydrogen sulfide plays an important role in the global sulfur cycle and climate regulation, but it is also important in understanding interactions between trace metals, complexing ligands, and phytoplankton. In seawater hydrogen sulfide exists as a dissolved gas, free ions, dissolved metal-sulfide complexes, and as particulate metal sulfides. Total dissolved sulfide (free+complexed) therefore strongly affects metal cycling via complexation, and also participates in the global sulfur cycle via exchange with the atmosphere.
Data obtained in the last decade have conclusively shown that pico- to nanomolar concentrations of dissolved and particulate sulfide are found in the surface ocean. While removal processes for surface water hydrogen sulfide are readily apparent, namely oxidation processes and exchange with the atmosphere, the only well quantified source of hydrogen sulfide is the hydrolysis of another sulfur gas, carbonyl sulfide. However, recent field and laboratory studies demonstrate that marine phytoplankton are another quantitatively significant source of dissolved and particulate sulfide in aquatic systems. The production of particulate and dissolved sulfide by phytoplankton is affected by the concentrations of free metals and nutrients in the growth medium and growth stage of cells.
As part of this 3-year project, we are undertaking a thorough examination of the rates and mechanisms of hydrogen sulfide production by marine phytoplankton using an iterative laboratory- and field-based approach. Our specific research objectives are:
To measure total dissolved and particulate sulfide production rates by several coastal and oceanic phytoplankton taxa under environmentally relevant conditions using continuous cultures.
To examine environmental (light, nutrients, free trace metals) and physiological (e.g., growth rate) factors affecting hydrogen sulfide production.
To elucidate the primary mechanisms and pathways of dissolved and particulate sulfide production.
To assess the utility of sulfur isotopes measurements for quantifying the contributions of biotic and abiotic production of hydrogen sulfide, and evaluating various biotic pathways for its production.
To compare field measurements from coastal and open ocean sites to verify lab results, and to enable us to compile a more detailed and quantitative description of the hydrogen sulfide cycle in marine surface waters and its implications for trace metal cycling.
Results and Links
5. Nutritional factors promoting algal blooms in the lower Chesapeake Bay.
Funded by the Virginia Water Resources Research Council
Harmful algal blooms (HABs) appear to be increasing in their geographical extent and frequency and have resulted in severe economic and public health impacts around the world, including the United States and Virginia. Harmful species can elicit adverse effects either directly, by the production of potent toxins that kill or harm fish (or people), or indirectly, through the production of excessive biomass and eutrophication. Effects of excessive production of algal biomass include: shading of submerged vegetation, disruption of food web dynamics and structure, and oxygen depletion as blooms decay. Species that form HABs represent a variety of taxa that occur naturally in the environment and may "bloom" when environmental conditions are altered to give them a competitive advantage over other co-occurring taxa.
The late spring/early summer plankton communities of the lower Chesapeake Bay (Virginia) contain a number of potentially harmful algal bloom species (e.g., the dinoflagellates Pfiesteria piscicida, Prorocentrum minimum, Gyrodinium galatheanum, Katodinium rotundatum, Cochlodinium heterolobatum, and Gymnodinium spp.) that can reach bloom densities. Increases in the occurrence of HABs, including dinoflagellate species in the lower Chesapeake Bay, have been attributed to changes in water quality in a variety of locations; specifically, the enrichment of estuarine waters with dissolved organic material (DOM) relative to inorganic nutrients. Elevated DOM concentrations can result from direct inputs of organic wastes, such as runoff from animal farms or human waste from septic fields and/or inefficient sewage treatment, or indirectly, as a result of nutrient recycling. However, with the exception of Pfiesteria research programs, there are no studies being undertaken to understand the processes and interactions whereby water quality parameters influence algal abundance and the occurrence of harmful algal blooms in Virginia waters.
Negative economic and environmental impacts due to HABs have already been reported in Virginia's estuarine waters. Because blooms are already occurring and may increase either directly or indirectly as a result of inputs of organic or inorganic nutrients or through recycling processes, it is important to identify and understand the nutritional factors promoting blooms. It is crucial that we understand the processes and pathways through which nutrients become available to these organisms so that we can: (1) mitigate the effects of blooms that result from natural or cultural eutrophication of water bodies, and (2) prevent their appearance in locations that have not previously experienced blooms or their economic and environmental repercussions. Until we understand these processes we cannot develop management strategies to protect water quality and Virginia's finfish and shellfish fisheries.
Results and Links
6. Acquisition of two Mass Spectrometer Systems for the Analysis of C,H,N,O,S Stable Isotopes in Biological, Environmental, Geochemical Systems.
Funded by the National Science Foundation
Co-PI:
This project funded the purchase of an Isotope Ratio Mass Spectrometer which will be used to measure isotopic ratios in particulate and gas samples. This instrument can be interfaced with a gas chromatography system as well as an elemental analyzer.
Results and Links
Pending Research Projects:
"Biocomplexity in the Environment: Assessing biological, chemical, physical and anthropogenic factors affecting productivity, N2 fixation, and elemental cycling in a coastal environment." (1 Jan. 2004 - 31 Dec. 2008), The National Science Foundation. Co-PI's are John Donat and Peter Ross Edwards (Dept. of Chemistry and Biogeochemistry, ODU), Joaquim Goes (Bigelow), Ajit Subramanium (University of Maryland), Fei Chai and Huijie Xue (University of Maine).
"Competitive interactions among organisms that use organic nutrients: The case of Aureococcus anophagefferens and bacteria." (1 Oct. 2003 - 30 Sept 2006), The Ecology and Oceanography of Harmful Algal Blooms (ECOHAB), Co-PI is Elizabeth Minor (Dept. of Chemistry and Biogeochemistry, ODU).
"Extracellular proteolytic enzyme activity in phytoplankton mixotrophs: their role in organic material mobilization and utilization." (1 Jan. 2004 - 30 Dec. 2006), The National Science Foundation. Co-PI is Diane Stoecker, University of Maryland, Horn Point Environmental Laboratory.
"Exploring mechanisms for organic matter preservation in the marine water column and sediments using mass spectrometry and NMR." (1 Jan. 2004 - ; 31 Dec 2006), The Department of Energy, PI is Elizabeth Minor (Dept. of Chemistry and Biogeochemistry, ODU). | 
