Use of Formalin-Preserved Collections to Infer Trophic Indicators of Marine Zooplankton from Stable Isotopes

Formalin preservation affects the stable isotope composition of zooplankton samples, thus limiting analysis valuable collections covering large time intervals. Here, we compare different procedures for correcting bias caused by formalin in δ13C and δ15N community samples. Zooplankton samples representative seasonal variations period 2000–2009 were collected off A Coruña (NW Spain). Part sample was immediately dried analysed δ13C, δ15N, elemental within 3 years collection. These values used as unpreserved reference. The remaining preserved 4% formaldehyde aliquots obtained after a ranging from to more than 10 storage originally Additionally, copepod fraction total biomass determined Corrections effects based on ordinary least squares regression had uncertainties, while mass balance corrections change C:N ratio (only possible δ13C) overestimated reference values. However, either simple mean difference between dry or complex generalised additive models considering seasonality, biomass, storage, produced estimations with relatively low uncertainty. Our results highlight importance determining specific correction solutions each collection before reconstructing series. Furthermore, uncertainties associated estimates can be sensitivity assess their potential impact interpretation