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Nutrient enrichment as a result of anthropogenic activity concentrated along the land-sea margin is increasing eutrophication of near-shore waters across the globe. Management of eutrophication in the coastal zone has been ' hampered by the lack of a direct method to trace nitrogen sources from land into coastal food webs. Stable isotope data from a series of estuaries receiving nitrogen loads from 2 to 467 kg N ha-' yr-' from the Waquoit Bay watershed, Cape Cod, Massachusetts, indicate that producer and consumer 15N-to-14N ratios record increases in wastewater nitrogen inputs. Nitrate from groundwater-borne wastewater introduces a '"N-enriched tracer to estuaries. This study explicitly links anthropogenically derived nitrogen from watersheds to nitrogen in estuarine plants and animals, and suggests that wastewater nitrogen may be detectable in estuarine biota at relatively low loading rates, before eutrophication leads to major changes in species composition and abundance within estuarine food webs.

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The importance of chemosynthetic nutritional pathways was examined for macrofaunal invertebrates (Ͼ300 m) from methane seeps in the Gulf of Alaska (4,413-4,443 m), on the Oregon margin (590 m), and on the northern California slope [Eel River margin] (520 m) by use of natural abundance stable isotopic data. Seep macrofauna exhibited lighter ␦ 13 C and ␦ 15 N values than those in nonseep sediments, but isotopic signatures varied among seep sites. Macrofaunal isotopic signatures indicated chemosynthetically fixed carbon sources with a significant contribution from methane-derived carbon (MDC) in macrofauna from sediments of pogonophoran fields (average ␦ 13 C, Ϫ46.44‰, 32%-51% MDC) and Calyptogena phaseoliformis beds (average ␦ 13 C, Ϫ40.89‰, 12%-40% MDC) in the Gulf of Alaska and in microbial mat sediments on the Oregon margin (average ␦ 13 C, Ϫ43.80‰, 20%-44% MDC). Lesser influence of MDC was noted in macrofauna from sediments of Calyptogena pacifica beds on the Oregon (average ␦ 13 C, Ϫ33.38‰, 0%-27% MDC) and California (␦ 13 C, Ϫ25.10‰, 0%-22% MDC) margins and from California microbial mat sediments (␦ 13 C, Ϫ22.23‰, 0%-5% MDC). Although most macrofauna appeared to be heterotrophic, light ␦ 15 N and ␦ 13 C values together provided evidence for chemoautotrophic symbioses in selected taxa. Carbon isotopic signatures were consistent with consumption of methane-oxidizing archaea by some dorvilleid polychaetes (␦ 13 C, Ϫ90.62‰ and Ϫ73.80‰) and with grazing on filamentous sulfur bacteria by gastropods and polychaetes from the Oregon and California seeps. The importance of chemosynthetic trophic pathways varies regionally and among microhabitats, taxonomic groups, and feeding guilds.The potential for chemosynthetically fixed carbon to support large endosymbiont-bearing invertebrates and to fuel entire animal communities in the ocean was first realized about two decades ago (Felbeck et al. 1981;Cavanaugh 1983). Since the discovery of chemosynthesis as a major nutritional pathway at hydrothermal vents, other reducing systems have been found in which energy is supplied mainly through chemosynthetic production (Paull et al. 1985). Methane, hydrocarbon and brine seeps, whale falls, some hypoxic settings, sewage outfalls, and seagrass beds are now known to support filamentous chemoautotrophic bacterial mats and invertebrates with chemoautotrophic endosymbionts (Fisher 1990;Cavanaugh 1994;Conway et al. 1994;Sibuet and Olu 1998). Although most attention has been on AcknowledgmentsWe thank the Captain and crew of the R/V Atlantis, the ALVIN pilots, and the many scientists who participated in Voyage 3 Leg 37 for their help in collecting material from the Gulf of Alaska and Oregon margin. We thank the crews of the R/V Thompson (Leg 118) and ROV Jason for help with collections on the Eel River margin. David James and Shelly Walther provided invaluable assistance with sample collection and processing at sea and in the laboratory. We thank Chris Schander, Larry Lovell, Leslie Harris, Jim McLean, Heiko Sahling, Eve Southwar...

Trophic ecology has benefitted from the use of stable isotopes for the last three decades. However, during the last 10 years, there has been a growing awareness of the isotopic biases associated with some pre-analytical procedures that can seriously hamper the interpretation of food webs. We have assessed the extent of such biases by: (1) reviewing the literature on the topic, and (2) compiling C and N isotopic values of marine invertebrates reported in the literature with the associated sample preparation protocols. The factors considered were: acid-washing, distilled water rinsing (DWR), sample type (whole individuals or pieces of soft tissues), lipid content, and gut contents. Two-level ANOVA revealed overall large and highly significant effects of acidification for both delta(13)C values (up to 0.9 per thousand decrease) and delta(15) N values (up to 2.1 per thousand decrease in whole individual samples, and up to 1.1 per thousand increase in tissue samples). DWR showed a weak overall effect with delta(13)C increments of 0.6 per thousand (for the entire data set) or decrements of 0.7 per thousand in delta(15) N values (for tissue samples). Gut contents showed no overall significant effect, whereas lipid extraction resulted in the greatest biases in both isotopic signatures (delta(13)C, up to -2.0 per thousand in whole individuals; delta(15)N, up to +4.3 per thousand in tissue samples). The study analyzed separately the effects of the various factors in different taxonomic groups and revealed a very high diversity in the extent and direction of the effects. Maxillopoda, Gastropoda, and Polychaeta were the classes that showed the largest isotopic shifts associated with sample preparation. Guidelines for the standardization of sample preparation protocols for isotopic analysis are proposed both for large and small marine invertebrates. Broadly, these guidelines recommend: (1) avoiding both acid washing and DWR, and (2) performing lipid extraction and gut evacuation in most cases.