Publications
Poster for 4th USHAB meeting 2007
Abstracts
Thessen, A.E., Q. Dortch, T.M. Soniat, and G.J. Doucette. 2001. Oyster grazing on toxic and non-toxic Pseudo-nitzschia. ERF 2001, St. Pete Beach, FL, Nov. 4-8, 2001.
Pseudo-nitzschia spp. are chain-forming diatoms that sometimes produce domoic acid, a potent neurotoxin that causes Amnesic Shellfish Poisoning (ASP). Despite high abundances of Pseudo-nitzschia over Louisiana oyster (Crassostrea virginica) beds, there have been no documented cases of ASP in the state. Two possible explanations are that oysters cannot feed on long, pointed chains or they discriminate against toxic cells while grazing. To test these hypotheses, short-term (<2hr) grazing experiments were conducted with non-toxic P. delicatissima and toxic P. multiseries. Oysters (75 to 85 mm) were collected in the field, maintained on flowing ambient seawater, and then starved for 48 hours. Pseudo-nitzschia cultures (cells approx. 50 microns: 4 cells/chain median chain length) were added at approximately 10^6 cells/liter to containers with individual oysters and to controls with no oysters or killed oysters. Grazsing was monitored by measuring decreases in in vivo fluorescence. Earlier studies showed that cell counts and fluorescence had a linear correlation. Oysters grazed rapidly on both toxic and non-toxic Pseudo-nitzschia and cells appeared in feces within 1 hour. Thus, it is unlikely that the absence of ASP in Louisiana is due to the inability of oysters to consume long chains of pointed cells or toxic cells.
Thessen, A.E., Q. Dortch, T.M. Soniat, and G.J. Doucette. 2002. Oyster grazing on toxic and non-toxic diatoms. NSA 2002, Mystic, CT, Apr 14-18, 2002.
Pseudo-nitzschia spp. are chain-forming diatoms that sometimes produce domoic acid, a potent neurotoxin that causes Amnesic Shellfish Poisoning (ASP). Despite high abundances of Pseudo-nitzschia over Louisiana oyster (Crassostrea virginica) beds, there have been no documented cases of ASP. Two possible explanations are that oysters cannot feed on long, pointed chains or they discriminate against toxic cells while grazing. Short-term (<2 hr) grazing experiments were conducted with non-toxic P. pseudodelicatissima, toxic P. multiseries (22-87 mm/cell, depending on species and clone; 4 cells/chain median chain length), Thalassisiora weisfloggii (15-23 mm), and Ditylum brightwellii (70-140 mm). Oysters (73 to 85 mm) were collected in the field, maintained on flowing ambient seawater, and then starved for 48 hours. Cultures were added at approximately 106 cells/liter to containers with individual oysters and to controls with no oysters or killed oysters. During experiments grazing was monitored by measuring decreases in in vivo fluorescence, but cell counts and volumes were also measured. Oysters grazed rapidly on all diatoms and cells appeared in feces within 1 hour. Grazing rates, based on fluorescence, were lower on both types of Pseudo-nitzschia than for the other diatoms, but those differences may not be sustained when grazing is based on cell volume/carbon.
Thessen, A.E., D.K. Stoecker, and B.C. Boicourt. 2003. Chesapeake Bay tributaries during the spring drought of 2002: a temporary return to less eutrophic conditions. ERF 2003, Seattle, WA, Sept 14-18, 2003.
The year 2002 was unusually dry, with widespread drought conditions in the Chesapeake Bay watershed. We examined two Bay tributaries, the Choptank River and Patuxent River, during spring cruises and found that the resulting reduction in freshwater flow was associated with record-high salinities, lower inorganic nutrients (particularly nitrate + nitrite), reduced eutrophication, and much lower chlorophyll a levels when compared with twenty years of historical data from the Chesapeake Bay Program. Of special interest were the spring phytoplankton assemblages. Unusually low concentrations of bloom-forming dinoflagellates were seen at most stations during 2002, however potential microzooplankton community grazing on small, bloom-forming dinoflagellates remained significant. This suggests temporary return to a planktonic community in which there are tight bottom-up (nutrient limitation) and top-down (microzooplankton grazing) controls on dinoflagellate bloom formation.
Thessen, A.E., D.K. Stoecker, P. Tango, S. Morton, and D. Caron. 2003. The presence of domoic acid in Pseudo-nitzschia from the Choptank River, a Chesapeake Bay tributary. 2nd symposium on Harmful Marine Algae in the U.S., Woods Hole, MA, December 9-13, 2003.
Pseudo-nitzschia is a toxic diatom that produces domoic acid (DA), the neurotoxin responsible for Amnesic Shellfish Poisoning (ASP) and Domoic Acid Poisoning (DAP) which affects humans through contaminated shellfish and marine mammals and birds through contaminated fish. Three clones of Pseudo-nitzschia were isolated from the Choptank River, one in November 2002 and two in April 2003. All three clones were tested for domoic acid activity using the receptor binding assay and ASP direct cELISA test kits. Only the November clone was found to be toxic, displaying 0.08 pg DA-equl/cell in exponential phase and .438 pg DA per cell in stationary phase. While the presence of Pseudo-nitzschia has been documented in the lower Bay since the early 1980's, this is the first record of toxic Pseudo-nitzschia in the Chesapeake Bay area. Historical data suggests that Pseudo-nitzschia abundances have been increasing and spreading throughout the Bay over the past five years. Based on algal community monitoring by Maryland Department of Natural Resources between 2000-2002, 50% of the water samples containing Pseudo-nitzschia had concentrations above levels requiring mandatory testing of shellfish meats in Denmark and New Zealand. No known toxic events have occurred in Maryland, however, increasing Pseudo-nitzschia abundances and the presence of domoic acid in the food chain could have an impact on the future of the Chesapeake Bay shellfish industry, wild vertebrate populations and public health.
Thessen, A. E. and D. K. Stoecker. 2005 Growth and domoic acid production in several species of Pseudo-nitzschia grown with different nitrogen sources. 3rd symposium on Harmful Marine Algae in the U.S., Asilomar, CA, October 2-7, 2005.
Some species of the diatom genus Pseudo-nitzschia are known to produce the neurotoxin domoic acid (DA) which is responsible for Amnesic Shellfish Poisoning in humans and Domoic Acid Poisoning in animals. It has previously been shown that Pseudo-nitzschia has higher growth rates on NO3 and NH4, but higher toxin production on urea. We performed growth studies on adapted cultures of Pseudo-nitzschia using 8 cultures of at least 4 species grown on NO3, NH4 and urea to investigate differences in growth rate and toxin production. We also performed growth vs. irradiance studies on one species of Pseudo-nitzschia to determine growth saturating light levels at different temperatures.
Thessen, A. E., H. A. Bowers, D. K. Stoecker and D. W. Oldach. 2006 Pseudo-nitzschia spp. and domoic acid in Maryland and Virginia waters. 12th International Conference on Harmful Algae, Copenhagen, Denmark, September 4-8, 2006.
Some species of the diatom genus Pseudo-nitzschia are known to produce the neurotoxin domoic acid (DA) which is responsible for amnesic shellfish poisoning in humans and domoic acid poisoning in animals. Current phytoplankton monitoring by Maryland Department of Natural Resources identifies Pseudo-nitzschia in water samples via light microscopy as either P. seriata or P. pungens. From 2002 to 2006 water samples were collected throughout the Chesapeake Bay (Maryland and Virginia), the coastal bays, and the Delaware coast for culture isolation, toxin analysis and Pseudo-nitzschia enumeration and species identification via TEM. Four species of Pseudo-nitzschia were identified in Maryland and Virginia waters (P. multiseries, P. fraudulenta, P. pungens and P. calliantha). Pseudo-nitzschia multiseries, P. calliantha and P. fraudulenta have been isolated from field samples, cultured in the laboratory and sequenced. Domoic acid was found in 6 of 14 cultures and in some field samples containing Pseudo-nitzschia. Pseudo-nitzschia was most abundant in the southern portion of the Chesapeake Bay from January to March. The data suggest that Pseudo-nitzschia in the Chesapeake Bay region is more abundant at higher salinities and during colder months.