Collaborative Research: The Effect of Iron-complexing Ligands on Iron Availability to Phytoplankton in HNLC Waters of the Subarctic Pacific Ocean

Collaborators:

Mark L. Wells and Mary-Jane Perry (University of Maine)

William P. Cochlan  (Romberg Tiburon Center - SFSU)

Funding Agency:

National Science Foundation – Chemical Oceanography

Summary:

The central hypothesis guiding this project is that Fe-complexing ligands in High Nitrate Low Chlorophyll (HNLC) waters regulate which phytoplankton groups can access iron, and, as a consequence, these ligands control the longer-term evolution of phytoplankton to natural (or anthropogenic) Fe enrichments.  Specific goals of our research, utilizing novel deck-board manipulation experiments in HNLC waters of the western North Pacific Ocean during 2004 (SEEDS-II aboard the R/V Kilo Moana) and in the eastern North Pacific Ocean during 2006 (PAPA-SEEDS aboard the R/V T.G. Thompson) are:

1. 1)to determine how different presumed ligand analogs, as well as seawater isolates of natural ligands, affect Fe availability to the resident phytoplankton species of offshore HNLC waters, and
   

2. 2)to determine if the ligands produced in response to Fe enrichments behave similarly to the ambient ligands, or if they have a significantly different effect on how the ecosystem evolves over the longer term, and
   

3. 3)to investigate whether historical exposures to different levels of Fe inputs results in conditioning of the phytoplankton that changes their ability to respond to different Fe-containing ligand blends.
   

Expected Results: In addition to providing fundamental data on how two natural classes of marine Fe(III) complexing ligands influence Fe availability to different types of phytoplankton, we will:

1. 1)identify the synthetic ligand analogs that best mimic the natural ligand classes with respect to Fe uptake,
   

2. 2)quantify how changes in the ligand consortium resulting from Fe enrichment alters the relative availability of Fe and thus the community trajectory, and
   

3. 3)evaluate whether proximity to Fe sources, or historical iron inputs to HNLC waters affects the ability of organisms to extract Fe from ligand complexes.
   

The Effects of Iron Complexing Ligands on the Long Term Ecosystem Response to Iron Enrichment of HNLC Waters

(the laboratory component of the NSF field project described above)

Collaborators:

Mark L. Wells and Mary-Jane Perry (University of Maine)

William P. Cochlan  (Romberg Tiburon Center - SFSU)

Funding Agency:

U.S. Department of Energy – Ocean Carbon Sequestration Research Program

Objectives:

The central hypothesis of this project is that natural iron-complexing organic ligands in seawater differentially regulate iron availability to large (microplankton) and small (nano and picoplankton) class of phytoplankton, and thereby strongly influence the potential carbon sequestration in High Nitrate Low Chlorophyll (HNLC) regions of the ocean. Detailed observations during IronEx II (eastern equatorial Pacific) and SOIREE (Southern Ocean) indicate that the diatoms began re-experiencing Fe stress even though dissolved Fe concentrations remained elevated in the patch. A more detailed understanding of the effects of Fe complexing ligands on long-term ecosystem structure and carbon cycling is essential to ascertain the potential efficiencies of carbon sequestration in the oceans and the potential sustainability of Fe enrichment as an effective C sequestration strategy The specific goals of the proposed work are to employ novel manipulation experiments to:

1. 1)determine how different natural and synthetic Fe chelators affect Fe availability to phytoplankton species that are representative of offshore HNLC waters,
   

2. 2)elucidate how the changes in absolute concentrations of these chelators (such as observed during IronEx II and SOIREE) will affect the ecosystem response beyond the normal (1-4 week) period of observations, and
   

3. 3)ascertain how changes in the ligand composition affect cell sinking and aggregation rates - measures of the efficiency of carbon sequestration to the deep.
   

Experimental Approach:

Our primary emphasis is the utilization of semi-continuous and continuous cultures in the laboratory and at sea to measure how a suite of natural ligand analogs, as well as Fe-complexing ligands isolated from seawater, affect Fe availability to phytoplankton. Growth rates, macronutrient utilization rates, and physiological parameters (variable fluorescence, cell size, Fe use efficiencies, and light dependent rates of carbon and Fe uptake) will be used to ascertain the organism-specific responses to Fe supplied in these different chemical forms with and without elevated UV treatment. The relationship between ligand types and individual cell sinking rates and the kinetics of cell aggregation will be determined to better assess the linkage between Fe ligands and the export of carbon and macronutrients to the deep. Laboratory findings will be combined with field programs in the North Pacific Ocean during 2004 and 2006 to assess how ligand substrates affect the differential supply of Fe to members of the phytoplankton assemblage, and how they influence the kinetics and magnitude of carbon uptake and ultimately planktonic carbon sinking rates.

Expected Results:

In addition to providing fundamental data on how the two natural classes of marine Fe(III) complexing ligands influence Fe availability to different types of phytoplankton, we will:

1. 1)identify synthetic ligand analogs that best mimic the natural ligand classes with respect to Fe uptake,
   

2. 2)quantify how changes in the ligand consortium resulting from Fe enrichment alters the relative availability of Fe and thus the community trajectory,
   

3. 3)measure the effect of the two ligand classes on the efficiency of carbon and macronutrient (primarily nitrogen substrates) incorporation into biomass,
   

4. 4)quantify changes in cell sinking rates and coalescence efficiencies as a function of ligand type, and
   

5. 5)determine ligand effects on community level carbon sequestration and export potential in field experiments with natural population cultures in HNLC waters.
   

ECOHAB-PNW: Ecology and Oceanography of Toxic Pseudo-nitzschia in the Pacific Northwest Coastal Ocean

Collaborators:

B. Hickey (lead PI) and E. Lessard (Univ. Washington)

V. Trainer (lead PI; NOAA Northwest Fisheries Science Center)

M. Foreman, A. Pena, and R. Thomson (DFO, Canada)

M.L Wells and L. Connell (Univ. Maine)

William P. Cochlan  (Romberg Tiburon Center - SFSU)

Funding Agencies:

NOAA/NSF

Summary:

This collaborative project studies the physiology, toxicology, ecology and oceanography of toxigenic Pseudo-nitzschia diatom species off the Pacific Northwest coast, a region in which both macro-nutrient supply and current patterns are primarily controlled by seasonal coastal upwelling processes. Recent studies suggest that the seasonal Juan de Fuca eddy, a nutrient rich retentive feature off the Washington and British Columbia serves as a "bioreactor" for the growth of phytoplankton, including diatoms of the genus Pseudo-nitzschia (PN). Existing ship of opportunity and prior research data are consistent with the working hypothesis that the seasonal Juan de Fuca eddy is an initiation site for toxic PN that impact the Washington coast and that upwelling sites adjacent to the coast are less likely to develop toxicity. The long term project goal is to develop a mechanistic basis for forecasting toxic PN bloom development here and in other coastal regions in Eastern Boundary upwelling systems. Our specific study objectives are:

1. 1)to determine the physical/biological/chemical factors that make the Juan de Fuca eddy region more viable for growth and sustenance of toxic PN than the nearshore upwelling zone, and
   

2. 2)to determine the combination of environmental factors that regulate the production, accumulation, and/or release of DA from PN cells in the field, and
   

3. 3)to determine possible transport pathways between DA initiation sites and shellfish beds on the nearby coast.
   

The objectives of this project are currently being met using an integrated suite of field and laboratory studies during a series of three-week cruises, moored bio/chem/physical sensors as well as circulation and biophysical modeling in our study area that includes both the eddy and also a typical coastal upwelling region. The key factors responsible for high cell densities of toxigenic PN spp. and the variable levels of cell toxicity are investigated with on-deck incubation studies and comprehensive in situ measurements including macronutrients (nitrate, phosphate and silicate), micronutrients (Fe, Cu), bacteria and grazing abundance as well as photosynthetic radiation, stratification and velocity shear. Aging of blooms is studied by following drogued patches of water both from the eddy and nearshore upwelling regions. Toxification of coastal shellfish will be determined using beach sampling sites maintained by the Olympic Region HAB program. A coupled biophysical model of the region enhanced with assimilated survey data will be used to examine the potential for bloom generation in offshore eddy and nearshore upwelling regions (e.g., stratification, nutrient sources, strength and timing) as well as to assess transport pathways of toxic PN to the coast under a variety of environmental and physiological conditions.  ECOHAB-PNW cruises to date include:

R.V. Wecoma, ECOHAB-PNW-I (June 2-23, 2003)

R.V. Wecoma, ECOHAB-PNW-II (Aug. 30 - Sept.19, 2003)

R.V. Atlantis, ECOHAB-PNW-III (Sept. 8 - 28, 2004)

R.V. Atlantis, ECOHAB-PNW-IV (July 6 - 27, 2005)

R.V. Melville, ECOHAB-PNW-V (Sept. 2 - 22, 2005)

R.V. T.G. Thompson, ECOHAB-PNV-VI (scheduled for Sept. 12 - Oct. 4, 2006)

Environmental controls on the growth and toxicity in blooms of Heterosigma akashiwo, a resident harmful alga of San Francisco Bay

Collaborator:

William P. Cochlan  (Romberg Tiburon Center - SFSU)

Funding Agency:

CALFED Bay-Delta Science Consortium – Science Support Funds

Massive blooms of the potentially toxic phytoplankton species Heterosigma akashiwo (Raphidophyceae) were observed for the first time in 2002 in central San Francisco Bay. At present we have a very limited knowledge of both the temporal and spatial distribution of this phytoflagellate, and its degree of toxicity to other members of the SF Bay estuarine community. The one-year pilot study is two-tired and includes both laboratory and field components. We have quantified the distribution of this harmful algal bloom (HAB) species in SF Bay, and investigated the environmental factors which contribute to its distribution and toxicity with a focus on the nitrogen (N) sources associated with anthropogenic inputs from human activities. Specifically we are determining if the various modes of nitrogenous nutrition and/or the degree of N-limitation, affect the toxicity of this flagellated phytoplankter.  This project builds on the laboratory and filed results obtained during a mini-project funded by Environmental Defense which partially supported Julian Herndon’s MA dissertation research on H. akashiwo.

Regulation of Iron Acquisition and Toxin Production in Harmful Algal Species

Funding Agency:

Natural Sciences and Engineering Research Council

Summary:

During the past decade the economic consequences of toxins from phytoplankton has influenced the resource use of shellfish, aquaculture fish and drinking water.  The phytoplankton responsible are termed “harmful algal bloom species” [HABs] and represent a diverse array of taxonomic species, linked together by the equally diverse negative impacts on the marine and freshwater environment. Recent reviews have documented the real expansion of HABs in the global coastal oceans and has highlighted factors deemed responsible for the proliferation of these cells: increased scientific awareness, cultural eutrophication, increased utilization of coastal waters, and the invasive nature of these organisms through global transportation (ballast waters, aquaculture seed stocks) 1.  One subset of these environmental regulations is the role of iron in the selection and toxicity of specific members of the HABs community.  We (and others) have shown that many coastal and open ocean regions and large freshwater bodies can undergo periods of extensive iron depletion that selects for specific phytoplankton communities. For the species selected for this study we have shown that the shift in iron status (from either iron-replete to iron-stress or from iron-stressed to iron replete) enhances the competitive ability of these cells and the levels of their corresponding toxin. My NSERC research program addresses 3 research needs.  Each project is linked by the principle that iron status of the harmful algal species determining the cell’s ability to scavenge iron from the environment and its ability to make a toxin.  My long-term goal is to improve understanding of the factors that influence the growth and toxicity of harmful algal species – organisms that are proliferating in our coastal and freshwater environments, reducing the quality of these resources and ecosystem health.

For this NSERC application, my short-term goal is to detail the role of iron as the environmental regulator of the production of 1.) domoic acid, a neurotoxin, from Pseudo-nitzschia sp., 2.) brevetoxin-like organics from two fish-killing flagellates, Chattonella and Heterosigma spp., and 3.) the hepatotoxic microcystin from the freshwater cyanobacterium, Microcystis.