MEPS 474:27-41 (2013)  -  DOI:

Response of the benthic food web to short- and long-term nutrient enrichment in saltmarsh mudflats

Pierre-Yves Pascal1,2,*, John W. Fleeger2, Henricus T. S. Boschker3, Hanan M. Mitwally4, David S. Johnson5

1UMR 7138, Equipe Biologie de la Mangrove, Laboratoire de Biologie Marine, Université des Antilles et de la Guyane,
97159 Pointe-à-Pitre, Guadeloupe, France
2Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA
3Center for Estuarine and Coastal Ecology, Netherlands Institute of Ecology, 4400 AC Yerseke, The Netherlands
4Oceanography Department, Faculty of Science, Alexandria University, 21511 Alexandria, Egypt
5The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA

ABSTRACT: We examined the responses of biota at or near the base of the benthic food web to nutrient enrichment in salt marsh mudflats in Plum Island estuary (Massachusetts, USA). To simulate eutrophication, nitrate and phosphate loading rates were increased 10- to 15-fold in creeks fertilized for 2 mo (i.e. short-term enrichment) or 6 yr (chronic enrichment). We found that benthic invertebrate community structure was not altered by nutrient enrichment, although the abundance of epifaunal, but not infaunal, grazers increased. Short-term enrichment had no effect on the food web, but significant changes were detected with chronic enrichment. Grazing experiments with 15N-enriched bacteria and 13C-enriched benthic algae revealed higher per capita ingestion rates of benthic microalgae by nematodes, copepods and hydrobiid snails in the creek with chronic nutrient enrichment where isotope composition also indicated that algae increased in dietary importance. The fraction of bacterial biomass grazed was not affected by nutrient enrichment; however, the fraction of benthic algal biomass grazed increased by 235% with chronic enrichment. This higher grazing pressure was partly the result of dietary changes (increases in per capita feeding rate or a change in selection) but was mostly due to an increased abundance of the grazing consumer with the highest biomass, the snail Nassarius obsoletus. This increased top-down control partially masked the bottom-up effects of nutrient enrichment on algal biomass and helps explain the slow and inconsistent response of microalgal biomass to chronic nutrient enrichment previously observed in this estuary. Our research shows that eutrophication may subtly affect benthic food webs before large, sustained increases in algal biomass are observed.

KEY WORDS: Nutrient enrichment · Benthic food web · Bacteria · Benthic microalgae · Meiofauna · Nassarius obsoletus · Grazing rates

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Cite this article as: Pascal PY, Fleeger JW, Boschker HTS, Mitwally HM, Johnson DS (2013) Response of the benthic food web to short- and long-term nutrient enrichment in saltmarsh mudflats. Mar Ecol Prog Ser 474:27-41.

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