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)

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.