MEPS 330:49-65 (2007)  -  doi:10.3354/meps330049

Using stable isotopes and quantitative community characteristics to determine a local hydrothermal vent food web

Derk C. Bergquist1,*, James T. Eckner2, Istvan A. Urcuyo3, Erik E. Cordes4, Stephane Hourdez5, Stephen A. Macko6, Charles R. Fisher2

1Marine Resources Research Institute, South Carolina Department of Natural Resources, 217 Fort Johnson Road, Charleston, South Carolina 29412, USA
2Department of Biology, The Pennsylvania State University, 208 Mueller Laboratory, State College, Pennsylvania 16802, USA
3Department of Biology, Gettysburg College, 300 N. Washington Street, Gettysburg, Pennsylvania 17325, USA
4OEB Department, Harvard University, 3079 BioLabs, 16 Divinity Avenue, Cambridge, Massachusetts 02138, USA
5CNRS, UPMC, UMR 7127, Equipe Ecophysiologie: Adaption et Evolution Moleculaires, Station Biologique, 29680 Roscoff, France
6Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22903, USA

ABSTRACT: To investigate food web structure in diffuse flow vent environments, an entire macrofaunal community associated with a single aggregation of the tubeworm Ridgeia piscesae was collected from a vent field on the Juan de Fuca Ridge in the NE Pacific. All members of the community were identified and enumerated, and the biomass and stable carbon (δ13C) and nitrogen (δ15N) isotope ratios were determined for almost all taxa. Symbiont-bearing invertebrates (primarily R. piscesae) accounted for a vast majority of the biomass of the community, and 3 presumably grazing bacterivorous gastropods dominated the biomass of the consumer fauna. Biomass and abundance of individuals declined from the bacterivore to the scavenger/detritivore to the predator feeding guild. Several species (a folliculinid ciliate, Idas washingtonia, Provanna variabilis) possessed unique stable isotope signatures, suggesting the possibility of symbiotic relationships with autotrophic bacteria. Stable isotope values varied widely between and occasionally within species in the lowest consumer levels suggesting a great diversity of food source 13C and 15N composition. Based on the distinct isotopic values of 3 bacterivores, 3 potential pools of isotopically-distinct microbial production were identified. The 4 highest-biomass predatory species (all polynoids) possessed δ13C and δ15N values consistent with a diet that included the tubeworm R. piscesae, a species comprising 83% of the total biomass in the collection, and the gastropod Depressigyra globulus, a species comprising 10% of the total biomass in the collection. A potential specialist predator (Clypeosectus curvus) on folliculinid ciliates was also identified. Overall the study suggested a dominant pattern of energy transfer from microbial producers to symbiont-bearing siboglinid tubeworms, various bacterivores (gastropods, polychaetes and pycnogonids), and detritivorous polychaetes to predaceous polynoids.

KEY WORDS: Food web · Trophic structure · Community structure · Hydrothermal vent · Juan de Fuca Ridge · Stable isotopes · Diffuse flow · Ridgeia piscesae

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