Prior Research

Assimilation rates of dissolved organic carbon by photomixotrophic estuarine phytoplankton

James L. Pinckney, University of South Carolina
May 2013 – April 2016
Agency: National Science Foundation – Biological Oceanography Program

Phytoplankton, traditionally viewed as primary producers at the base of aquatic food webs, provide an energy source for higher trophic levels. However, some phytoplankton species function as both primary producers and heterotrophic secondary consumers. Phytoplankton that are photosynthetically competent but also take up AND assimilate organic compounds are classified as facultative mixotrophs or, more simply, photomixotrophs. Unfortunately, we currently have few estimates of the proportion of the phytoplankton community that function as photomixotrophs, their rate of secondary production, or their temporal variation in abundance. Current paradigms about trophodynamics in marine systems do not consider this potentially important “alternative” pathway for energy flow for phytoplankton. The implication is that we may be missing a significant, fundamental process that affects carbon cycling and trophodynamics in estuarine systems. Furthermore, changes in the DOC composition due to anthropogenic alterations may result in changes in phytoplankton community structure and possibly promote the proliferation of harmful algal bloom species. In terms of ecosystem function, even moderate rates of photomixotrophy could potentially alter our current understanding of phytoplankton productivity, overall C turnover, competitive interactions, and energy transfer in estuarine environments. The proposed research will use a novel approach to provide quantitative measures of the in situ rates and magnitudes of “facultative heterotrophy” in natural, estuarine phytoplankton communities over seasonal time scales in a representative estuarine ecosystem.
The purpose of the proposed research is to apply a unique 14C radiolabeling technique to quantify the in situ assimilation rates of DOC by estuarine photomixotrophs and estimate the amount of DOC converted to phytoplankton biomass by photomixotrophy over seasonal time scales. This information will provide new insights into carbon dynamics in estuaries, the contribution of DOC to estuarine food webs, and the importance of photomixotrophy in determining the structural and functional characteristics of estuarine phytoplankton communities.

INTELLECTUAL MERIT The proposed research will provide new insights into the potential importance of an alternative source of C (DOC) and pathway for phytoplankton production. Successful demonstration that a significant fraction of the production of estuarine phytoplankton is by photomixotrophy would have major implications for the way we currently view C flow in these systems. The proposed research has a reasonable likelihood of altering the current paradigms for estuarine primary productivity as well as providing new evidence for mechanisms of competitive interactions between phytoplankton species in mixed, natural assemblages. The proposed research will also provide first-order approximations of labile DOC turnover by phytoplankton and will be one of the few measurements ever obtained for an estuary. Research results will contribute to an improved knowledge of relevant and underlying ecophysiological, organismal, and community-level processes involving carbon cycling in an estuarine environment.

BROADER IMPACTS This project will address the broader impacts criterion of “advancing discovery and understanding while promoting teaching, training, and learning”. The proposed research will provide support for a graduate student, summer support for an undergraduate assistant, and involve upper level undergraduates as lab interns. Undergraduate interns, recruited from the Marine Science Program at USC, will participate in sample analyses and learn to operate laboratory instrumentation. Furthermore, the field bioassays will be added as a module in our required Marine Science undergraduate field course, MSCI 460 – “Field & Lab Investigations in MSCI”.


Ecological characterization of bioluminescence in Mangrove Lagoon, Salt River Bay, St. Croix, USVI

Link to Final Report

James L. Pinckney (PI)*
Dianne I. Greenfield
Claudia Benitez-Nelson
Richard Long
University of South Carolina

Chad Lane
Carmelo Tomas
University of North Carolina at Wilmington

Bernard Castillo
Kynoch Reale-Munroe
Marcia Taylor
University of the Virgin Islands

David Goldstein
Zandy Hillis-Starr
National Park Service, Salt River Bay NHP & EP

Start Date: 01 August 2012
Duration: 1 year

Salt River Bay National Historical Park and Ecological Preserve (SARI) is located along the north/central coast of St. Croix, U. S. Virgin Islands. Mangrove Lagoon is located on the east side of Salt River Bay, south of Hemer’s Peninsula. This oval-shaped lagoon is a small (250 m x 130 m), shallow (<4 m) manmade embayment that was created by a hotel/marina development project in the 1960’s-1970’s which dredged an existing salt pond connecting a previously enclosed pond to Salt River Bay. Bioluminescence in the waters of Mangrove Lagoon has become an ecotourism attraction for St. Croix. Over the last 15 years, night kayak tours have been conducted to observe the natural bioluminescence in Mangrove Lagoon. This project will study the bioluminescence and associated conditions within Mangrove Lagoon and provide scientific information to assess potential effects of MREC operations on this biological phenomena. The primary objective of the proposed research is to perform a comprehensive investigation of planktonic bioluminescence phenomena in Mangrove Lagoon to determine causal mechanisms and identify key factors necessary for the preservation of bioluminescent activity. This study will provide definitive identification of the bioluminescent dinoflagellate species, correlations between water quality parameters and dinoflagellate (as well as all phytoplankton) abundance, a determination of which nutrients are potentially limiting the growth of dinoflagellates (and phytoplankton), the spatial distribution, abundance, and a chronology of previous blooms based on preserved cysts, how the bacterial community relates to dinoflagellate abundances, and approximations of water residence time. Provisions have been made for the involvement of stakeholders, students (elementary to college), educators, and the general public through a carefully designed outreach program. The final product will be of local interest and provide essential baseline data for assessing future changes in water quality and bioluminescent dinoflagellates in Mangrove Lagoon.


Collaborative Proposal: Th(IV) and Pa(IV,V) binding to exopolymeric acid polyscaccharides in marine environments

Peter Santschi and James L. Pinckney

National Science Foundation – Chemical Oceanography
2004 to 2008

Th(IV) and Pa(IV,V) isotopes are important proxies in oceanographic investigations, such as, fortracing particle dynamics and particulate organic matter (POC) fluxes out of the euphotic zone through the use of 234Th/POC ratios, and for studying boundary scavenging, paleoproductivity and ocean circulation through the use of 231Pa/230Th ratios. Even though almost routine, these approaches still have to rely on poorly constrained, empirically determined variable isotope ratios or ratios to POC. Previously conducted laboratory and field investigations suggest that Th(IV) removal could be controlled through binding by exopolymeric acid polysaccharide (APS) rich biomolecules, produced by either phytoplankton or bacteria. Whether Pa(IV,V) is fractionated during binding to APS or other phases with respect to Th(IV) and concomitant Pa(V) reduction to Pa(IV) is largely unknown, but is important to the use of the Pa/Th ratio as a proxy in oceanographic applications. The proposed interdisciplinary experimental approaches will require instrumental approaches for characterization studies, in combination with both controlled laboratory and field experimentation. Laboratory studies consist of uptake experiments to a number of substrates, including purified APS harvested from phytoplankton and bacterial cultures to be used in Th(IV) and Pa(IV,V) binding assessments. The most important analytical task will be to better characterize, at the molecular level, the newly discovered strongly Th(IV) complexing APS of ~13 kDa molecular weight. The proposed field program will include collection and extraction of diverse types of organic matter for comparison to laboratory studies, as well as the determination of temporal and spatial variations of radiochemical and biochemical parameters. Macromolecular organic ligands likely have a biological origin and spatial and temporal variations in their source function, which could also lead to variations in the above ratios. Phytoplankton and bacteria production and degradation rates and processes will be evaluated in cultured and Gulf of Mexico samples and compared to the presence of Th(IV) and Pa(IV,V)-binding biomolecules to determine specific molecules which contain strong actinide binding ligands, and responsible microorganism(s) producing these biomolecules.

Intellectual Merit: The intellectual merit of the proposed research is the elucidation of the chemical basis of oceanographic tracer applications of Th and Pa isotopes. Sources and sinks of Th- and Pa-binding molecules will be evaluated, as well as the cause of fractionation of Pa/Th ratios during scavenging. Our initial focus on laboratory experiments and cultures will likely make significant advances in understanding the importance of chemical structure in macromolecular ligand-actinide interactions and in determining potential sources and sinks for these ligands in the marine environment.

Broader Impact: A number of unique broader impacts will result from this project that are relevant to our fundamental concerns of ocean scavenging and carbon cycling and oceanography as a whole. The proposed work will be an integral part of the research education of 2 graduate students who will be able to take advantage of the diverse state-of-the-art infrastructural and scientific resources. The proposed research will not only have a broad impact on education in environmental science and oceanography, but the new results will impact a number of oceanographic disciplines.


Anhydrophilic, Halotolerant Microbial Mats of San Salvador Island, Bahamas

Hans W. Paerl, Timothy F. Steppe, James L. Pinckney, and Alan Decho

National Science Foundation – Microbial Observatories

2002 to 2008

The Bahamian Islands, characterized by San Salvador (24 05′ N, 74 30′ W), contain numerous hypersaline lakes and ponds (45 to 160 ppt). These lakes are subject to intense irradiance (> 2300 µE m-2 s-1), high temperatures (> 30 C) and chronic nutrient (e.g. nitrogen) depletion. On San Salvador, luxuriant microbial mats blanket the shallow sediments in many of the lakes and contribute significantly to production and material flux within the lakes. The ability of the mats to fix atmospheric N2 is important for ensuring N-availability and sustaining productivity. On a yearly basis, water availability is a key determinant for mat productivity and growth. When lake-levels recede during the dry season (December to April), extensive areas of the mats are desiccated. During desiccation, the mats incur further osmotic, temperature and irradiance stresses. Due to the severe water-stress conditions, the mats typify microbial growth at .the edge of life. To minimize the effects of decreased water availability incurred through osmotic and desiccation stress, many prokaryotic organisms produce secondary metabolites such as trehalose and glycine betaine and/or exopolymeric substances (EPS). Because water stress is an overarching characteristic of the lakes, a large portion of the carbon and nitrogen budgets may be coupled to the production and degradation of metabolites produced in response to water stress. For the San Salvador mats, as well as other non-hypersaline mat communities world wide, EPS represent a significant structural component, protective feature, and pool of reduced carbon. However, little work has been done to assess regulation of EPS production, content, and degradation in relationship to the structure, composition, stress endurance, and nutrient flux of mat communities. This project will establish a microbial observatory for the hypersaline lakes and ponds of San Salvador Island. In addition to representing hypersaline biomes, the lakes of San Salvador are pristine systems free of anthropogenic impacts. As such, they enable us to exam how large scale climatic oscillations and other natural environmental changes impact microbial community structure and function. The overall research objective of this study will be to assess the influence water availability has on structural diversification, community composition, production, and carbon sequestration in microbial mats. The specific goals for this observatory are to: 1) Describe the structural and microbial diversity of the different mat communities in relation to water availability. 2) Assess the influence water availability has on primary production, EPS production, and EPS degradation. 3) Isolate and characterize novel anhydrophilic organisms and biogeochemically important genes. 4) Develop a conceptual model linking climate fluctuations, water budgets, primary production, and EPS production and turnover. Fieldwork will be based out of the Bahamian Field Station (BFS) on San Salvador Island, which is close, and ideally suited to support proposal activity. Every year, the BFS hosts students and researchers from a multitude of United Sates and overseas institutions. In cooperation with the BFS staff, a prime focus for this project will be the establishment of educational and research opportunities for students wishing to better understand the structure, function, and environmental controls of halotolerant, extremophilic microbial communities on San Salvador. Information and data for this project will be made available at BFS, through the project’s central web site, publications, and educational efforts.


Collaborative Research-BES: FerryMon, unattended water quality monitoring
utilizing advanced environmental sensing

Hans W. Paerl, Richard A. Luettich, Tammi L. Richardson, James L. Pinckney

National Science Foundation – BES – Environmental Engineering

2006 to 2009

Funds are requested to enhance real-time detection and quantification of key waterquality indicators, and improve data management and outreach capabilities for the ferrybased, unattended water quality program for the Albemarle-Pamlico Sound System, NC, FerryMon ( Objectives: Newly-developed in-line spectral fluorometers, the Algae Online Analyzer (AOA) will be installed on two ferries crossing the Pamlico Sound and its largest sub-estuary, the Neuse River Estuary. In addition, an automated vertical profiler (AVP), equipped with sensors similar to those on the ferries, will be installed in Pamlico Sound to provide a vertical dimension to the water quality data being collected by FerryMon. Specifically, the AOA and associated sensors will facilitate early detection, quantification and characterization (as to environmental controls) of a key
indicator of water quality, harmful algal blooms. These advancements in sensing will greatly enhance spatial detection and characterization of trends in water quality and habitat conditions over the entire range of relevant physical, chemical and biological time scales (minutes to months and beyond). This enhanced capability is both highly relevant and timely given a protracted period of increased tropical storm and hurricane activity that is impacting estuarine and coastal water quality and fisheries resources in unpredictable yet important
ways. These improvements will greatly facilitate calibration, and interpretation of remotely sensed indicators of water quality (e.g., photopigments, turbidity), enabling investigators to “scale up” to this large estuarine ecosystem. Funds will also be used to upgrade data management, communication and outreach, enabling FerryMon to most effectively and fully integrate with complementary observational programs (SECOORA, SeaCOOS, Hydrological Observatories, state, federal and local environmental monitoring programs), and to enhance FerryMon’s educational and public outreach capabilities. This instrumentation package and its deployment are readily transferable to other large estuarine and coastal ecosystems served by ferries, other “ships of opportunity”, moorings and other platforms.

Intellectual merit: The proposed improvement in real-time environmental observational and assessment capabilities will enhance real-time interdisciplinary studies aimed at identifying, quantifying and distinguishing anthropogenic and climatic drivers of biogeochemical and ecological change in large water bodies (lake, riverine, estuarine and coastal) that have traditionally been difficult to monitor and assess. Particular emphasis will be placed on examining the impacts of a recent rise in tropical storm and hurricane activity on water
quality and habitat condition and change in Pamlico Sound, the nation’s second largest estuarine complex and among its most important fisheries resources. An interdisciplinary team, including experts in estuarine ecology, limnology, water quality, hydrodynamics, algal systematics and ecophysiology, sensor deployment and data management has been assembled to accomplish project goals. The broader impacts of the proposed research include educational and societal benefits resulting from an improved understanding of the ecosystem scale
water quality and habitat impacts of efforts to manage nutrients and other pollutants in estuaries and other large water bodies facing increasing anthropogenic and climatic stress. Additional broader impacts will results from the interdisciplinary research and educational opportunities inherent in this work. For example, in addition to undertaking integrated assessments of water quality and ecological change, the research team will train high school, undergraduate and graduate students, technicians and post-doctoral researchers; the next
generations of environmental scientists and engineers.


Detection of the red-tide dinoflagellate Gymnodinium breve (Karenia brevis)

James L. Pinckney & Erla B. Ornölfsdöttir

Texas Parks and Wildlife Department
1999 to 2000

Phytoplankton, including Gymnodinium breve and other HAB species, have distinct spectral absorbance characteristics due to accessory photosynthetic pigments located within chloroplasts. Photopigments, including chlorophylls, carotenoids, and phycobilins serve as useful, sensitive, and diagnostic indicators of dominant microalgal functional groups (e.g., diatoms, chlorophytes, dinoflagellates, cyanobacteria, cryptophytes, pelagophytes, etc.). The technology for detection and spectral (absorbance, fluorescence) characterization of photopigments has rapidly evolved and diversified, to the extent that methodologies based on specific pigment detection capabilities can now be routinely employed to identify and estimate phytoplankton standing stock, community structure, and biodiversity. Among the relevant technologies, high performance liquid chromatography (HPLC) is now used worldwide by researchers and water quality agencies to quantify the species composition and relative biomass of taxonomic groups in the phytoplankton community.

The carotenoid gyroxanthin-diester is an uncommon accessory photopigment that provides a relatively unique biomarker for Gymnodinium breve. Gyroxanthin-diester concentrations have been positively-correlated with G. breve standing crop (both cell numbers and total chlorophyll a) during blooms in Florida in 1994-95. Subsequent work with cultures incubated under a range of light and nutrient conditions has shown that gyroxanthin-diester concentrations are consistent, generally comprising 3 – 10% of the total carotenoid pigment pool in G. breve. In addition, the chromatographic and absorption characteristics of gyroxanthin-diester are distinct, providing for easy and definitive recognition in HPLC-derived pigment chromatograms. The limits of detection for G. breve abundance using this pigment-based approach may be as low as 1.0 x 106 cells.

Another dinoflagellate species that occurs in Texas coastal waters, Gymnodinium mikimotoi, has accessory photopigments similar to G. breve as well as the marker pigment gyroxanthin. In contrast, Gymnodium dorsum has a quite different photopigment profile. G. dorsum has the primary carotenoid peridinin, but lacks gyroxanthin and 19′ hexanoyloxyfucoxanthin.

Special thanks to Dr. Dave Millie and Dr. Pat Tester for providing cultures of G. breve and to Mr. Matt Wargo for cultures of G. mikimotoi and G. dorsum.

Use of High-Resolution Spatial Mapping to Estimate Plankton Response to Freshwater Inflows Entering Galveston Bay: Importance to Watershed Development and Ecosystem Health

Stephen E. Davis, Daniel L. Roelke, James L. Pinckney

The Galveston Bay Estuary Ecosystem Research Program
2004 to 2006

Freshwater inflow and degree of nutrient loading to an estuary have long been understood as factors contributing to water quality and ecosystem health. In some estuaries, poor health, reduced productivity, and even losses of coastal wetlands have been linked to reductions in freshwater input. Estuarine inflows have been shown to govern estuarine biogeochemical processes, affecting the abundance (i.e. availability) of nutrients and organic matter. In Texas estuaries, freshwater inputs have been implicated as a primary factor controlling biological productivity. Studies have shown that freshwater inputs affect productivity of juvenile brown shrimp, macrophyte productivity, root:shoot ratios, and species diversity, and benthic macrofaunal and meiofaunal densities and diversity.

Factors equally important, but not as often addressed in estuarine studies, include the magnitude of freshwater inflows and nutrient loading, the mode of nutrient loading (e.g., continuous vs. pulsed flows, and frequency of pulsed flows), and the ratios of potentially limiting nutrients within the load. Experiments by Buyukates and Roelke (2000) using natural plankton assemblages from the Nueces River Estuary (TX) showed that the mode of nutrient delivery had a profound impact on the plankton community structure. Assemblages receiving the nutrient load in a pulsed mode had less accumulated phytoplankton biomass and supported greater secondary productivity, while assemblages receiving a continuous inflow resulted in a phytoplankton bloom and the demise of the zooplankton community.

Understanding the spatial and temporal variability in estuarine water quality and plankton assemblages is a difficult task. Often there is a tradeoff between temporal and spatial resolution. Surface water monitoring programs generally focus on a few select sites over a range of temporal scales (weekly to monthly). On the other hand, remote sensing can capture the necessary spatial variability for a few rudimentary parameters, but algorithms are not very accurate for these shallow water coastal systems. Tying these different types of observations (i.e. fixed station and remote) to estuarine inflow patterns is further complicated by a lack of knowledge on loading rates, estuarine morphology and circulation patterns, and attenuation rates of pulsed events.

Herein, we propose a two-year study (pending availability of funds in the 2nd year) to track the spatial variability in water quality in the Galveston Bay Estuary, as mediated by temporal variability in freshwater inflows from the Trinity River. Moreover, we seek to understand the effects of this spatio-temporal hydrologic variability on phytoplankton community dynamics and water column production along the estuarine salinity axis and throughout the entire bay complex.


Physical Controls on Benthic Fluxes of Microalgae and Particulate Organic Matter

in Estuarine Environments

George Voulgaris, James L. Pinckney & Jeffery Morin
Marine Science Program, USC

South Carolina Sea Grant
February 2008 to January 2010

In estuaries, the flux of particulates between water and sediment is dependent on turbulence generated by tidal and wind-induced flows (including surface waves). The suspended particulates consist of three major components; benthic microalgae, non-living particulate organic matter, and sediment. Quantification of the relative amounts of these three types of particulates under a variety of tidal and wind-induced turbulence conditions is necessary to construct computational models of sediment and particulate fluxes in estuarine habitats. Furthermore, the physical, biogeochemical, and ecological fate of resuspended particulates depends on the type of particle. For example, resuspended benthic microalgae may be a valuable food resource for filter feeders (oysters) as well as zooplankton and juvenile fish. Particulate organic matter demineralization is probably enhanced when resuspended in oxic water column conditions promoting rapid and efficient recycling of nutrients. The size distribution of resuspended sediments under different turbulence conditions has major implications for sediment transport and deposition processes. Thus quantification of the effects of shallow water turbulence on the material fluxes of different particle types will provide insights into the importance of this process in governing the source, transport, and fate of benthic microalgae, particulate organic matter, and sediments across the sediment-water boundary of estuaries. Furthermore, these results can be coupled with existing hydrodynamic models to provide system-wide estimates of benthic-pelagic exchange of particulates.

The overall objective of this study is to create a biogeochemical module that can be integrated with hydrodynamic models to simulate fluxes of benthic microalgae (BMA), non-living particulate organic matter (POM), and the particle size distribution of suspended sediments (SS) under turbulence conditions of tidal and wind-induced flows. The short-term objectives to be achieved within the 2-year length of the proposed project are:

1) Determine experimentally the relationship between physical hydrodynamic forcing and re-introduction of BMA, POM, and SS into the water column, in a tidally dominated environment for different seasons.

2) Differentiate the particle dynamics of benthic sediment and BMA.

3) Parameterize benthic fluxes of BMA into a geochemical module that can be integrated in physical numerical models.

Experiments will utilize high frequency (>2Hz) flow and BMA (Chlorophyll a) measurements in the benthic boundary layer. These will be accompanied by collection of water column samples for particle characteristic analysis in the laboratory that will be used to verify/calibrate the automated measurements. Experiments will be carried out over full tidal cycles (spring and neap) at North Inlet for two different seasons (winter – summer) with different productivity characteristics. North Inlet is part of the Winyah Bay estuarine system and is composed of many shallow creeks traversing a large salt marsh encompassed by Debidue Island, North Island and the Mainland. The marsh is flooded twice over a 24 hour period and the sediments are generally a mixture of sand and silty clay.

The benthic boundary layer (BBL) measurement system will consist of: (i) Acoustic Doppler Velocimeter (ADV) that measures mean flow and turbulence; (ii) Optical Backscatter Instrument (OBS) that measures bulk material in the water column; (iii) Laser in situ Scattering Transmissometer (LISST) for in-situ particle size measurements; (iv) Acoustic Backscatter Sensor (ABS) for high resolution (<1cm) profiles of inorganic particle size concentrations; and (v) Fluorometer for in vivo Chlorophyll a measurements. The system will be deployed in a tidal creek in North Inlet, SC.


Effect of Sublethal Concentrations of Agricultural Herbicides on the Structure and Function of Estuarine Phytoplankton Communities

James L. Pinckney and Jean Marie Buschur

South Carolina Sea Grant

March 2006 – February 2007


To determine the short-term sublethal effects of environmentally-relevant concentrations of atrazine (under high and low nutrient concentrations) on estuarine phytoplankton community structure and function. The specific hypotheses that will be tested are:

a. Short-term exposure of estuarine phytoplankton to low atrazine concentrations (1.00 µg l-1) under low nutrient conditions promotes shifts in the relative abundance of phytoplankton taxonomic groups and species and a reduction in primary productivity.

b. Under high (non-limiting) nutrient conditions, the effects of sublethal concentrations of atrazine (1.00 µg l-1) on phytoplankton biomass, community composition, and primary productivity are less severe (i.e., are significantly different) than the effects under nutrient-limiting conditions.

c. Trace concentrations of atrazine (0.10 µg l-1) have no effect on estuarine phytoplankton biomass, community composition, or primary production.


Tasks and Methodology:

Short-term Phytoplankton Bioassays will be used to measure initial phytoplankton responses to different levels of atrazine and nutrient exposure. The purpose of these experiments is to determine the effects of a range of atrazine/nutrient concentrations on phytoplankton primary productivity and biomass of specific algal groups (i.e., diatoms, cyanobacteria, dinoflagellates, cryptophytes, etc.) in natural estuarine phytoplankton assemblages. These data will be used to assess “who” responds to the different levels of atrazine treatments under ambient (light, nutrient, temperature, etc.) conditions. This experimental approach is critical for understanding the mechanisms underlying phytoplankton community responses and dynamics in estuarine ecosystems.

Habitat alteration and loss of biodiversity due to pesticide contamination is rapidly emerging as major ecological threat for wetland and estuarine ecosystems. In aquatic ecosystems, phytoplankton are usually the most atrazine-sensitive biotic components. The proposed research will directly address SC Sea Grant Strategic Goal 3 under the Priority Topic “Investigations of the cumulative effects on key indicator marine organisms of low level, sub-chronic exposure to chemical contamination due to increasing human activities”. In this project, the key indicator species will be phytoplankton and the ecological indicators will be phytoplankton community composition and primary productivity. The chemical contaminants will be a common herbicide (atrazine) in waters entering many South Carolina estuaries, growth-limiting nutrients (nitrate & phosphate), and the interactive effects of atrazine and nutrients to simulate pulsed river discharge events.



Title: Gymnodinium breve in the Gulf of Mexico: Gyroxanthin-based estimates of carbon-specific growth rates under varying environmental conditions

Investigators: Tammi L. Richardson and James L. Pinckney
Institution: Dept. of Oceanography, Texas A&M University, College Station, TX

EPA Project Officer: Gina Perovich
Project Period: 1 September 2001- 31 August 2003

Project Summary: Determination of in situ growth rates of HAB-forming species is critical to an accurate description of bloom dynamics but there are currently few reliable methods of directly determining growth rates on natural populations. Photopigment radiolabeling, a method for measuring carbon (C)-specific growth rates of phytoplankton, is based on the determination of synthesis rates of chlorophylls and carotenoids using photosynthetically-assimilated 14C as a radiotracer. This work will examine the use of radiolabeling of the biomarker pigment gyroxanthin as a diagnostic tool for determining growth rates of natural populations of the toxic dinoflagellate Gymnodinium breve (recently renamed Karenia brevis) in Texas and Florida coastal waters. The utility of field measurements will be assessed by laboratory experiments that compare gyroxanthin radiolabeling-derived growth rates to those determined by time-series measurements of cell numbers, total chlorophyll a and particulate C and nitrogen (N) in batch and semi-continuous cultures of G. breve. A second and closely related objective is to characterize the role of nutrients, primarily N, in modifying the growth rate of G. breve. To examine the possible role of anthropogenic N inputs (e.g. in agricultural runoff or atmospheric deposition) in the persistence and proliferation of G. breve blooms, growth rate variations in response to increased N availability will be measured. Growth rate responses to decreasing N availability as might occur during the course of a bloom will also be examined to address the possible role of growth rate declines in the termination of bloom events. Since the physiological and ecological effects of nutrients are tightly coupled to photophysiological responses, experiments will be performed under varying irradiances. Field work with G. breve will consist of gyroxanthin-radiolabeling measurements done at varying depths through the time course of blooms in Galveston Bay, Texas and on the Florida Shelf. In light of the possible relationships between anthropogenic nutrient discharges, coastal eutrophication, and HAB formation, this project has the potential to enhance our understanding of the mechanistic relationships between nutrients, light, and growth of G. breve and closely-related HAB species. Thus, this research will address informational needs and concerns of phytoplankton physiologists and ecologists as well as resource managers concerned about controls on HABs in estuarine and coastal waters.

Supplemental keywords: estuary, red tide, toxin, Gulf of Mexico, marine, ecological effects, aquatic, Texas, Florida, biology, ecology


Untreated urban effluent effects on phytoplankton community structure and function in Lake Pontchartrain, LA

James L. Pinckney
Marine Science Program and Department of Biological Sciences
University of South Carolina

The floodwaters being pumped back into Lake Pontchartrain contain toxic chemicals, carcinogens, pathogens, and human waste. The rate of loading of these contaminants is unprecedented and presents a unique opportunity to describe ecosystem responses to this catastrophic event. Documentation of changes in phytoplankton community composition will provide a sensitive bioindicator for quantifiying changes in ecosystem processes following Hurricane Katrina. This proposal requests support to analyze phytoplankton samples collected by a Research Team at LSU. The overall objective is to quantify the short- and long-term responses of the phytoplankton community to massive inputs of untreated floodwaters into Lake Pontchartrain. This event offers a unique opportunity to observe how ecological processes in Lake Pontchartrain are altered following the catastrophic addition of millions of gallons of untreated effluent. Our research findings will be invaluable for developing models of how coastal ecosystems respond to catastrophic inputs of untreated urban wastewater.