Sea Briefs is a report on the results of the Mississippi-Alabama Sea Grant Consortium.
Editor: Melissa Schneider
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MASGC supports applied, interdisciplinary marine science research, education and outreach efforts to foster the sustainable development and management of the Mississippi and Alabama coasts and nearshore ecosystems of the Gulf of Mexico
there a better way?
Current federal guidelines use a fecal coliform indicator count in water samples to determine if shellfish beds should be closed to harvesting, but the presence of fecal coliforms does not necessarily infer contamination of the shellfish. Ruth H. Carmichael, Ph.D., a senior marine scientist at Dauphin Island Sea Lab and assistant professor of marine science at the University of South Alabama, wondered if there was a more accurate means of making this determination. Together with Peter Biancani, a graduate student from the University of South Alabama and Dauphin Island Sea Lab, and Josh Daskin, an undergraduate student from Brandeis University, and working in collaboration with the U.S. Food and Drug Administration (FDA), she began taking samples. Funding for the project was provided by the Mississippi-Alabama Sea Grant Consortium.
Carmichael’s research showed that at times ecological factors, such as oyster growth rates and survival rates, were not measurably affected by wastewater even though indicators in both the wastewater and the oyster tissues revealed biochemical evidence that the shellfish were affected by the wastewater. To prove a link between the wastewater and the material found in the shellfish tissue, the scientists used a combination of stable nitrogen isotopes specific to wastewater and a male-specific bacteriophage (MSB) as indicators. They selected MSB because it is less likely to be influenced by treatment and environmental factors and because it is more similar to the pathogens in wastewater that can make people sick.
Carmichael and her associates took samples from sites parallel to sites being tested by the FDA in the vicinity of the water treatment facility on McDuffie Island in Mobile Bay. Samples were collected at varying distances from the facility and over the course of a year. The team found that discharge from other sources confounded the fecal coliform indicators, making it difficult to specifically link indicators in the shellfish tissue back to the wastewater. No such difficulties were encountered using the stable nitrogen isotopes and the MSB.
Carmichael said the findings present a more accurate means of identifying contaminated shellfish relative to water treatment sites. The method currently employed sometimes results in unnecessary closures. Carmichael pointed out that cases of human infection have occurred even when a location is closed. It is her hope that the results of this project will have both short-term and long-term benefits.
In the short term, Carmichael sees potential uses in community planning, choosing aquaculture sites and seeding new oyster beds. In the long term, the benefits could apply to watermen, the general public and the shellfish industry as a whole. With a more accurate means of determining if a location should be closed, unnecessary closures will be less, which benefits watermen. This same level of accuracy could benefit the public by reducing the chances of consumption of contaminated shellfish. The shellfish industry could benefit as a whole as more shellfish can be harvested and sold while maintaining a higher degree of public health.
Results of the study are referenced in “Use of N stable isotope and microbial analyses to define wastewater influence in Mobile Bay” (Daskin, et. al., Marine Pollution Bulletin 56:5, pp. 860-868).