Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, occurs in coastal bays along the northeast coast of the United States. This species was identified in Chincoteague Bay, Maryland, in 1997 and has bloomed there since at least 1998. Time series of dissolved organic matter (DOM) concentrations and characteristics are presented for two sites in Chincoteague Bay: one that experienced a brown tide bloom in 2002 and one that did not. Characteristics of the bulk DOM pool were obtained using dissolved organic carbon (DOC) and ultraviolet-visible (UV-Vis) measurements (spectral slope and specific UV absorbance). High molecular weight DOM (HMW-DOM) was characterized in terms of DOC concentration, carbon:nitrogen (C:N) ratio, isotopic signature, and molecular-level characteristics as determined by direct temperature resolved mass spectrometry (DT-MS). Compositional changes in the DOM pool are associated with brown tide blooms, although a direct relationship between DOM characteristics and bloom development could not be confirmed. DOC measurements suggest that during the brown tide bloom, HMW-DOM was released into the surface water. UV-Vis analysis on the bulk DOM and molecular-level characterization of the HMW-DOM using DT-MS show that this material was optically active and more aromatic in nature. Based upon C:N ratio and HMW-DOC measurements, it appears that this HMW-DOM was more nitrogen enriched. Whether this material was released as exudates or was due to lysis of A. anophagefferens could not be determined.
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The authors wish to thank Peter Bernhardt and George Bo-neillo for their help in sampling and the chl a and brown tide cell enumeration, Dr. Dias and Deborah Hewlett for the use of the IRMS instrument for the analysis of our samples, and Dr. Burdige for the use of the Shimadzu TC-5000 TOC analyzer. The authors also wish to thank the Marine Science Consortium, Wallops Island for the use of their Greenbackville lab and the Virginia Institute of Marine Science for access to their Eastern Shore laboratory in Wachapreague. This study was funded by a grant from the U.S. Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) Program to M. Mulholland and E. Minor (NOAA Coastal Ocean Program ECOHAB Grant #NA160P1512). This is contribution number 118 from the U.S. ECOHAB Program.