title: delta(15)N and delta(13)C in the Mondego estuary food web: seasonal variation in producers and consumers.
abstract: Assessments of temporal variation in stable carbon and nitrogen ratios were used to examine seasonal trends of the water column and benthic food webs in the Mondego estuary (Portugal). There was a marked seasonality in weather and water column conditions, including nutrient supply and chlorophyll concentrations. In spite of the pronounced environmental changes, we found little evidence of seasonal variation in delta(13)C and delta(15)N of producers and consumers in the Mondego estuary, with a few notable exceptions. Nitrogen isotope ratios in macrophytes (Zostera noltii, Ulva sp., Enteromorpha sp., and Gracilaria sp.), and in two grazers (Idotea chelipes and Lekanesphaera levii) increased during late summer, with the highest delta(15)N values being measured in July, during a period of elevated temperatures and drought, which may have favored high rates of denitrification and heavier delta(15)N values. The results suggest that stable-isotope values from macrophytes and selected grazers are useful as tracers of seasonal changes in nitrogen inputs into estuaries, and that those of consumers reflect other factors beyond seasonal variations in N and C sources.
authors.affiliation: IMAR - Institute of Marine Research, Department of Zoology, University of Coimbra, 3004-517 Coimbra, Portugal. asbaeta@ci.uc.pt
authors.forename: Alexandra
authors.initials: A
authors.lastname: Baeta
authors.forename: Rute
authors.initials: R
authors.lastname: Pinto
authors.forename: Ivan
authors.initials: I
authors.lastname: Valiela
authors.forename: Pierre
authors.initials: P
authors.lastname: Richard
authors.forename: Nathalie
authors.initials: N
authors.lastname: Niquil
authors.forename: João C
authors.initials: JC
authors.lastname: Marques
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002247:Carbon Isotopes / Q000378:metabolism*; D056890:Eukaryota / Q000737:chemistry; D005399:Fishes / Q000378:metabolism; D020387:Food Chain; D007448:Invertebrates / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000378:metabolism*; D006109:Poaceae / Q000737:chemistry; D012621:Seasons; D012623:Seawater / Q000032:analysis
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes