Feeding on the edge: δ13C analysis of a macrofauna food web from disappearing seagrass beds in a polluted urban harbour – implications for biomonitoring and restoration efforts


  • R. L. France

    Corresponding author
    1. Dalhousie University, Faculty of Agriculture, Department of Environmental Sciences, Truro, Nova Scotia, Canada
    • Correspondence to: R.L. France, Dalhousie University, Faculty of Agriculture, Department of Environmental Sciences, PO Box 550, Truro, Nova Scotia, Canada, B2N 5E3. E-mail: rfrance@dal.ca

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  1. Thirty-five macrofaunal species were collected from several eelgrass (Zostera marina) beds in Boston Harbour to determine whether food provenance and carbon flow as measured by δ13C analysis differed for a seagrass community exposed to dense urbanization compared with those documented for populations distant from cities, and whether such isotopic determinations might be used for purposes of biomonitoring such disturbance.
  2. In support of other studies and a previous global synthesis, the majority of benthic and epibenthic fauna inhabiting Boston Harbour eelgrass beds were found to have δ13C values within the range, –20 to –17 ‰, indicative of epiphytic algae being the most important food source. However, the proportional abundance-weighted assessment of the distribution of individual δ13C measurements was found to be quite different from that revealed by non-quantitative, species-only assessments.
  3. Because the chink shell, Lacuna vincta, which was the only species to demonstrate primary assimilation of eelgrass δ13C, numerically dominated the benthic food web in Boston Harbour, over three-quarters of the total abundance of macroinvertebrates were likely to be directly dependent upon eelgrass carbon. Nevertheless, food web transfer, as measured through δ15N analysis, was extremely limited as no direct mechanism appeared to presently exist by which eelgrass carbon could be exclusively passed from chink shells to animals of higher trophic positions.
  4. The dietary fidelity of these animals while experiencing severe habitat loss due to anthropogenic pollution – neither a shift toward increased vascular plant detritivory nor toward increased planktonic algivory occurred – indicates that pathways of carbon flow may offer little use as an early warning biomonitor for gauging either individual stress or community-level disturbance from coastal development.
  5. Because epiphytic algae are the major food source for most macrobenthos species rather than the vascular plants themselves, the possibility exists that seagrass simulacra might be used as interim installations in order to sustain communities until such time as the aquatic conditions improve to such a degree as to enable the successful restoration of the degraded beds.

Copyright © 2013 John Wiley & Sons, Ltd.