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Marine Ecology Progress Series

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MEPS 526:11-19 (2015)  -  DOI:

Evidence of grazer control on nitrogen fixation by eelgrass epiphytes in a temperate coastal bay

Laura K. Reynolds1,4,*, Roxanne Marino2, Meredith F. Muth1, Natalie McLenaghan3, Melanie Hayn2, Anna Christina Tyler3, Karen J. McGlathery1, Robert W. Howarth2

1Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22903, USA
2Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA
3Thomas H. Gosnell School of Life Sciences, Rochester Institute of Technology, Rochester, New York 14623, USA
4Present address: University of California Davis, Department of Evolution and Ecology, Davis, California 95616, USA
*Corresponding author:

ABSTRACT: In this study, we present data to support the hypothesis that removal of epiphytes by grazers is an important control of nitrogen fixation in temperate seagrass meadows during the summer. Previous work in West Falmouth Harbor, Massachusetts, USA, found highest rates of epiphytic nitrogen fixation in the part of the harbor (Snug Harbor) with the greatest nitrogen load and the lowest phosphate concentrations, a somewhat paradoxical result suggesting that biogeochemical controls are not the major factor regulating this nitrogen fixation. Here we report that the density of invertebrate grazers on epiphytic algae (predominantly Bittiolum alternatum) was least in Snug Harbor, where nitrogen fixation rates were greatest. Reciprocal transplant experiments showed that seagrass shoots transplanted into Snug Harbor from the part of the harbor (Outer Harbor) where external nitrogen loading was lower but grazer densities were 4-fold higher, had a more than 5-fold increase in epiphytic nitrogen fixation after a 12 d incubation period. Shoots transplanted from Snug Harbor to Outer Harbor showed a large, rapid reduction in epiphytic nitrogen fixation rates after only 6 d, likely due to consumption of epiphytes. Our results suggest that trophic control is a potentially important determinant of epiphytic nitrogen fixation rates in temperate seagrass meadows.

KEY WORDS: Zostera marina · Nitrogen fixation · Herbivory · Nutrient cycling

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Cite this article as: Reynolds LK, Marino R, Muth MF, McLenaghan N and others (2015) Evidence of grazer control on nitrogen fixation by eelgrass epiphytes in a temperate coastal bay. Mar Ecol Prog Ser 526:11-19.

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