Marine Biology

, Volume 156, Issue 10, pp 2107–2120

Eutrophication and trophic structure in response to the presence of the eelgrass Zostera noltii

  • Alexandra Baeta
  • Ivan Valiela
  • Francesca Rossi
  • Rute Pinto
  • Pierre Richard
  • Nathalie Niquil
  • João C. Marques
Original Paper

Abstract

In estuaries, eelgrass meadows contribute to fundamental ecosystem functions of estuaries, providing food to several predators and buffering the negative effects of eutrophication. We asked whether the presence of the eelgrass Zostera noltii decreased the nitrogen concentration in the overlying water, affected the sources of nitrogen sequestrated by primary producers and changed the benthic and pelagic food web structures. We also studied the importance of these food webs in providing food to fish. We compared bare sediment to sediment covered by a Z. noltii meadow, and examined nutrient concentrations in the water column and δ15N in primary producers as indicators of anthropogenic inputs of nutrients. We then measured both δ13C and δ15N in the tissues of plants and consumers to establish food web structures. There were no differences in the concentrations and sources of nitrogen between sites. Rather, δ15N values indicated anthropogenic inputs of N (e.g. sewage discharges, agriculture) in both sites. There were no major differences in the structure of the planktonic food web, which was in part sustained by particulate organic matter and supported most predator fish, and in the structure of the benthic food web. Nonetheless, there were differences in the sources of food for omnivore consumers and for the detritivore Scrobicularia plana. Overall, the benthic food web did not use food derived from the eelgrass or macroalgae deposited on the substratum. Suspension feeders used particulate and sediment organic matter, whereas the δ13C and δ15N values of the other consumers indicated a likely contribution of benthic microalgae. Furthermore, in both habitats we found large variability in the isotope signatures of benthic macrofauna consumers, which did not allow distinguishing clearly different trophic groups and indicated a high level of omnivory and a mixed diet opportunistically making use of the availability of food in the surroundings.

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Alexandra Baeta
    • 1
    • 3
  • Ivan Valiela
    • 2
  • Francesca Rossi
    • 1
  • Rute Pinto
    • 1
  • Pierre Richard
    • 3
  • Nathalie Niquil
    • 3
  • João C. Marques
    • 1
  1. 1.Department of Zoology, IMAR, Institute of Marine ResearchUniversity of CoimbraCoimbraPortugal
  2. 2.The Ecosystems Center, Marine Biological LaboratoryWoods HoleUSA
  3. 3.Centre de Recherche sur les Ecosystèmes Littoraux Anthropisés, UMR6217, CNRS, IFREMERUniversité de La RochelleLa RochelleFrance

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