DOI: 10.5061/dryad.sj4fn
title: Data from: Environmental correlates of large-scale spatial variation in the δ13C of marine animals (and related published studies of carbon and nitrogen isotopic baselines)

description: Carbon stable isotopes can be used to trace the sources of energy
 supporting food chains and to estimate the contribution of different
 sources to a consumer’s diet. However, the δ13C signature of a consumer is
 not sufficient to infer source without an appropriate isotopic baseline,
 because there is no way to determine if differences in consumer δ13C
 reflect source changes or baseline variation. Describing isotopic
 baselines is a considerable challenge when applying stable isotope
 techniques at large spatial scales and/or to interconnected food chains in
 open marine environments. One approach is to use filter feeding consumers
 to integrate the high frequency and small-scale variation in the isotopic
 signature of phytoplankton and provide a surrogate baseline, but it can be
 difficult to sample a single consumer species at large spatial scales
 owing to rarity and/or discontinuous distribution. Here, we use the
 isotopic signature of a widely distributed filter-feeder (the queen
 scallop Aequipecten opercularis) in the northeastern Atlantic to develop a
 model linking base δ13C to environmental variables. Remarkably, a single
 variable model based on bottom temperature has good predictive power and
 predicts scallop δ13C with mean error of only 0.6 ‰ (3%). When the model
 was used to predict an isotopic baseline in parts of the overall study
 region where scallop were not consistently sampled, the model accounted
 for 76% and 79% of the large-scale spatial variability (101–104 km) of the
 δ13C of two fish species (dab Limanda limanda and whiting Merlangus
 merlangius) and 44% of the δ13C variability in a mixed fish community. The
 results show that source studies would be significantly biased if a single
 baseline were applied to food webs at larger scales. Further, when
 baseline δ13C cannot be directly measured, a calculated baseline value can
 eliminate a large proportion of the unexplained variation in δ13C at
 higher trophic levels.
description: Nitrogen and carbon
 stable isotope data for Queen scallop Aequipecten opercularis (Linnaeus,
 1758) (AphiaID: 140687) muscle tissueThe file comprises
 measurements of carbon and nitrogen stable isotope composition in the
 adductor muscle tissue of 535 individual Queen scallop Aequipecten
 opercularis sampled from northeast Atlantic shelf seas in 2001 and 2010.
 Data collection and existing analyses are described in the following
 publications: (1) Barnes, C., Jennings, S. & Barry, J.T. (2009)
 Environmental correlates of large-scale spatial variation in the δ13C of
 marine animals. Estuarine, Coastal and Shelf Science, 81, 368-374; (2)
 Jennings, S. & Warr, K.J. (2003) Environmental correlates of
 large-scale spatial variation in the δ15N of marine animals. Marine
 Biology, 142, 1131-1140; (3) Jennings, S. & Van der Molen, J. (2015)
 Trophic levels of marine consumers from nitrogen stable isotope analysis:
 estimation and uncertainty. ICES Journal of Marine Science, 72, 2289-2300.
 Additional descriptions of the data structure and data collection process
 are provided in the accompanying "readme"
 file.SIA_N_C_Aequipecten_opercularis_NEAtl_27092016_v1.csvSampling LocationsPDF map of of sampling locations.sampling_locations_d13C_d15N_Aequipecten_opercularis.pdf