Data from: Coupling biogeochemical tracers with fish growth reveals physiological and environmental controls on otolith chemistry

Biogeochemical tracers found in the hard parts of organisms are frequently
used to answer key ecological questions by linking the organism with the
environment. However, the biogeochemical relationship between the
environment and the biogenic structure becomes less predictable in higher
organisms as physiological processes become more complex. Here, we use the
simultaneous combination of biogeochemical tracers and fish growth
analyzed with a novel modeling framework to describe physiological and
environmental controls on otolith chemistry in an upwelling zone. First,
we develop increasingly complex univariate mixed models to describe and
partition intrinsic (age effects) and extrinsic (environmental parameters)
factors influencing fish growth and otolith element concentrations through
time. Second, we use a multivariate mixed model to investigate the
directionality and strength between element-to-element and growth
relationships and test hypotheses regarding physiological and
environmental controls on element assimilation in otoliths. We apply these
models to continuous element (Na, Sr, Mg, Ba, Li) and growth increment
profiles (monthly resolution over 17 years) derived from otoliths of reef
ocean perch (Helicolenus percoides), a wild-caught, site-attached, fully
marine fish. With a conceptual model, we hypothesize that otolith traits
(elements and growth) driven by environmental conditions will correlate
both within an otolith, reflecting the time dependency of growth and
element assimilation, and among individuals that experience a similar set
of external conditions. We found some elements (Sr:Ca and Na:Ca) are
mainly controlled by physiological processes, while other elements (Ba:Ca
and Li:Ca) are more environmentally influenced. Within an individual fish,
the strength and direction of correlation varies among otolith traits,
particularly those under environmental control. Correlations among
physiologically regulated elements tend to be stronger than those
primarily controlled by environmental drivers. Surprisingly, only Ba:Ca
and growth are significantly correlated among individuals. Failure to
appropriately account for intrinsic effects (e.g. age) led to inflated
estimates of among individual correlations and a depression of within
individual correlations. Together, the lack of among-individual
correlations of otolith traits in properly formulated models and the
biases that can be introduced by not including appropriate intrinsic
covariates suggest that caution is needed when assuming multi-elemental
signatures are reflective solely of shared environments.