title: Effects of formalin preservation on stable carbon and nitrogen isotope signatures in Calanoid copepods: implications for the use of Continuous Plankton Recorder Survey samples in stable isotope analyses.
abstract: Preserved and archived organic material offers huge potential for the conduct of retrospective and long-term historical ecosystem reconstructions using stable isotope analyses, but because of isotopic exchange with preservatives the obtained values require validation. The Continuous Plankton Recorder (CPR) Survey is the most extensive long-term monitoring program for plankton communities worldwide and has utilised ships of opportunity to collect samples since 1931. To keep the samples intact for subsequent analysis, they are collected and preserved in formalin; however, previous studies have found that this may alter stable carbon and nitrogen isotope ratios in zooplankton. A maximum ~0.9‰ increase of δ(15) N and a time dependent maximum ~1.0‰ decrease of δ(13) C were observed when the copepod, Calanus helgolandicus, was experimentally exposed to two formalin preservatives for 12 months. Applying specific correction factors to δ(15) N and δ(13) C values for similarly preserved Calanoid species collected by the CPR Survey within 12 months of analysis may be appropriate to enable their use in stable isotope studies. The isotope values of samples stored frozen did not differ significantly from those of controls. Although the impact of formalin preservation was relatively small in this and other studies of marine zooplankton, changes in isotope signatures are not consistent across taxa, especially for δ(15) N, indicating that species-specific studies may be required.
authors.affiliation: Marine Biology and Ecology Research Centre, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK. anthony.bicknell@plymouth.ac.uk
authors.forename: Anthony W J
authors.initials: AW
authors.lastname: Bicknell
authors.forename: Maria
authors.initials: M
authors.lastname: Campbell
authors.forename: Mairi E
authors.initials: ME
authors.lastname: Knight
authors.forename: David T
authors.initials: DT
authors.lastname: Bilton
authors.forename: Jason
authors.initials: J
authors.lastname: Newton
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Votier
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000032:analysis*; D033342:Copepoda / Q000737:chemistry* / Q000378:metabolism; D015925:Cryopreservation; D003625:Data Collection / Q000592:standards; D004784:Environmental Monitoring / Q000592:standards*; D005557:Formaldehyde / Q000737:chemistry*; D009587:Nitrogen Isotopes / Q000032:analysis*; D010933:Plankton; D015203:Reproducibility of Results; D013997:Time Factors; D014021:Tissue Preservation / Q000379:methods* / Q000592:standards
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D005557:Formaldehyde