1. Virginia Institute of Marine Science, Gloucester Point, Virginia 23062, National Marine Fisheries Service, Highlands, New Jersey 07732, Department of Chemistry, University of Florence, 50019 Sesto Fiorentino, Florence, Italy, Department of Environmental Science, University of Siena, I-53100 Siena, Italy, and Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, Maryland 20688