Stable isotopes demonstrate seasonally stable benthic-pelagic coupling as newly-fixed nutrients are rapidly transferred through food chains in an estuarine fish community

Cobain, M. R.D., McGill, R. A.R. and Trueman, C. N. (2023) Stable isotopes demonstrate seasonally stable benthic-pelagic coupling as newly-fixed nutrients are rapidly transferred through food chains in an estuarine fish community. Journal of Fish Biology, (doi: 10.1111/jfb.15005) (PMID:35099820) (Early Online Publication)

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Seasonal differences in the availability of resources potentially result in food web architecture also varying through time. Stable isotope analyses are a logistically simple but powerful tool for inferring trophic interactions and food web structure, but relatively few studies quantify seasonal variations in food web structure or nutrient flux across multiple trophic levels. We determined the temporal dynamics in stable isotope compositions (carbon, nitrogen and sulfur) of a fish community from a highly seasonal, temperate estuary sampled monthly over a full annual cycle. Sulfur isotope values in fish tissues discriminated among consumers exploiting pelagic and benthic resources but showed no seasonal variation. This implied limited change in the relative consumption of pelagic and benthic resources by the fish community over the study period despite major seasonal changes in phytoplankton biomass. Conversely carbon and nitrogen isotope values exhibited seasonality marked by the commencement of the spring phytoplankton bloom and peak chlorophyll concentration, with δ13C values following expected trends in phytoplankton growth physiology and variation in δ15N values coinciding with changes in major nitrogen sources to plankton between nitrate and ammonium. Isotope shifts in fish muscle were detected within two weeks of the peak spring phytoplankton bloom, suggesting a rapid trophic transfer of carbon and nitrogen along food chains within the estuarine food web during periods of high production. We therefore caution against the assumption that temporal averaging effectively dampens isotopic variability in tissues of higher trophic level animals in highly dynamic ecosystems such as temperate estuaries. This work highlights how stable isotope analyses can be combined with environmental data to gain broader understanding of ecosystem functioning, while emphasising the need for temporally appropriate sampling in stable isotope-based studies.

Item Type:Articles
Additional Information:This work was supported by a NERC SPITFIRE PhD studentship (award number 1498909), and a NERC LSMSF grant-in-kind (number EK272-08/16).
Status:Early Online Publication
Glasgow Author(s) Enlighten ID:McGill, Dr Rona
Authors: Cobain, M. R.D., McGill, R. A.R., and Trueman, C. N.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Journal of Fish Biology
ISSN (Online):1095-8649
Published Online:31 January 2022
Copyright Holders:Copyright © 2022 The Authors
First Published:First published in Journal of Fish Biology 2022
Publisher Policy:Reproduced under a Creative Commons License

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