Blooms of the brown tide pelagophyte, Aureococcus anophagefferens, have been reported in coastal bays along the east coast of the USA for nearly two decades. Blooms appear to be constrained to shallow bays that have low flushing rates, little riverine input and high salinities (e.g., >28). Nutrient enrichment and coastal eutrophication has been most frequently implicated as the cause of A. anophagefferens and other blooms in coastal bays. We compare N and C dynamics during two brown tide blooms, one in Quantuck Bay, on Long Island, NY in 2000, and the other in Chincoteague Bay, at Public Landing, MD in 2002, with a physically similar site in Chincoteague Bay that did not experience a bloom. We found that the primary forms of nitrogen (N) taken up during the bloom in Quantuck Bay were ammonium and dissolved free amino acids (DFAA) while the primary form of N fueling production at both sites in Chincoteague Bay was urea. At both Chincoteague sites, amino acid carbon (C) was taken up while urea C was not. Even though A. anophagefferens has the ability to take up organic C, during the bloom at Chincoteague Bay, photosynthetic uptake of bicarbonate was the dominant pathway of C acquisition by the >1.2 μm size fraction during the day. C uptake by cells <5.0 μm was insufficient to meet cellular C demand based on the measured N uptake rates and the C:N ratio of particulate material. While cells >1.2 μm did not take up much organic C during the day, smaller cells (>0.2 μm) did. Peptide hydrolysis appeared to play an important role in mobilizing organic matter in Quantuck Bay, where amino acids contributed substantially to N and C uptake, but not in Chincoteague Bay. Dissolved organic N (DON), dissolved organic C (DOC) concentrations and the DOC/DON ratio were higher and total dissolved inorganic N (DIN) concentrations were lower at the bloom site in Chincoteague Bay than at the nonbloom site in the same bay. We conclude that A. anophagefferens is capable of using a wide variety of N and C compounds, and that nutrient inputs, biotic interactions and the dominant recycling pathways determine which compounds are available and which metabolic pathways are active at a particular site.
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We would like to thank P. Bernhardt, J.-P. Simjouw, E. Cornfeld, A. Rocha, M. Watson and S. Reynolds for their help during fieldwork and laboratory analyses. C. Gobler and C. Lee also provided important contributions to this work. The staff at the Virginia Institute of Marine Sciences Eastern Shore Laboratory, especially Mark Luckenbach, P.G. Ross and G. Arnold provided assistance during field sampling and important information regarding the coastal bays of Virginia. Cathy Wazniak (MD Department of Natural Resources) and Brian Sturges (MD National Park Service) also contributed time and intellectual support for the Chincoteague Bay studies. We thank two anonymous reviewers for thoughtful comments on the manuscript. This work was supported by NY Sea Grant and a grant from the US ECOHAB Program to M. Mulholland. The ECOHAB Program is sponsored by the National Oceanic and Atmospheric Administration, Environmental Protection Agency, National Science Foundation, National Aeronautics and Space Administration, and Office of Naval Research. This is contribution #111 from the US ECOHAB Program. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or any of its subagencies.
- Aureococcus anophagefferens
- C uptake
- Dissolved inorganic N
- N uptake
- Peptide hydrolysis