MEPS 225:65-78 (2002)  -  doi:10.3354/meps225065

Use of chemosynthetic biomass by large, mobile, benthic predators in the Gulf of Mexico

Stephen E. MacAvoy1,*, Robert S. Carney2, Charles R. Fisher3, Stephen A. Macko1

1Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22903, USA
2Coastal Ecology Institute, Louisiana State University, Baton Rouge, Louisiana 70803, USA
3Biology Department, Pennsylvania State University, University Park, Pennsylvania 16802, USA
*Present address: Biology Department, 101 Hurst Hall, Ameri- can University, 4400 Massachusetts Ave. NW, Washington, DC 20016, USA.E-mail:

ABSTRACT: The Gulf of Mexico supports communities of chemoautotrophic and heterotrophic fauna associated with hydrocarbon seeps. The chemoautotrophic invertebrates, mostly dense epifaunal assemblages of mussels and tubeworms, derive their nutrition from symbiotic relationships with sulfide- or methane-oxidizing bacteria. The extent to which benthic predatory fauna feed on the chemoautotrophic assemblages has been an open question. Owing to differences in stable isotope values between chemosynthetic- and photosynthetic-derived biomass, isotopic characterization of predatory fauna would be useful in determining their dependence upon chemoautotrophs for food. Carbon and sulfur stable isotope analyses reveal that fishes with similar feeding strategies (rat tail [Nezumia sp.] and eels [Synaphobranchus sp., Ophicthus cruentifer and Dysomma rugosa]) have similar δ13C values (-32.7 and -42.5‰, respectively), reflecting chemoautotrophic carbon. Large vagrant predators/scavengers such as isopods Bathynomus giganteus, hagfish Eptatretus sp. and spider crabs Rochina crassa, have isotope values closer to oceanic ranges (δ13C: -20 to -18‰; δ34S: 18 to 20‰), although some individual Eptatretus sp. and R. crassa show a chemosynthetic component. Colonist invertebrates, such as the sea star (Sclerasterias cf. tanneri) and a predatory snail Buccinum canetae, have greatly depleted δ13C and δ34S values, indicating an almost 100% reliance on seep production. Nitrogen isotope ratios are depleted (-19‰) in some seep areas, and B. canetae and Synaphobranchus sp. reflect the 15N depletion (-10 and -3‰ respectively). On a species-specific basis, some mobile benthic predators from the background fauna obtain close to 100% of their nutrition from seep production, indicating that they are residents of the seeps. There is a high degree of movement in and out of the seep habitat by vagrant benthic predators, and although the majority derive most of their nutritional needs from photosynthetic production, the incorporation of chemosynthetic production is substantial.

KEY WORDS: Chemosynthetic production · Benthic marine predators · Stable isotopes

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