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

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 δ15N and a time dependent maximum ~1.0‰ decrease of δ13C were observed when the copepod, Calanus helgolandicus, was experimentally exposed to two formalin preservatives for 12 months. Applying specific correction factors to δ15N and δ13C 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 δ15N, indicating that species-specific studies may be required. Copyright © 2011 John Wiley & Sons, Ltd.

Genetic analysis of Continuous Plankton Recorder (CPR) samples

Genetic analysis of Continuous Plankton Recorder (CPR) samples is enabling greater taxonomic resolution and the study of plankton population structure. Here, we present some results from the genetic analysis of CPR samples collected in the North Sea and north-eastern Atlantic that reveal the impacts of climate on benthic-pelagic coupling and the food web. We show that pronounced changes in the North Sea meroplankton are related to an increased abundance and spatial distribution of the larvae of the benthic echinoderm, Echinocardium cordatum. Key stages of reproduction in E. cordatum, gametogenesis and spawning, are influenced by winter and spring sea temperature (January-May). A stepwise increase in sea temperature after 1987, which has created warmer conditions earlier in the year, together with increased summer phytoplankton, may benefit the reproduction and survival of this benthic species. Competition between the larvae of E. cordatum and other holozooplanlcton taxa may now be altering the trophodynamics of the summer pelagic ecosystem. In the north-eastern Atlantic the genetic analysis of fish larvae sampled by the CPR has revealed an unprecedented increase in the abundance of juvenile snake pipefish, Entelurus aequoreiis since 2002. We argue that increased sea surface temperatures in winter and spring when the eggs of E. aqueoreus, which are brooded by the male, are developing and the young larvae are growing in the plankton are a likely cause. The increased abundance of this species in Atlantic and adjacent European seas already appears to be influencing the marine food web.

Development and validation of a molecular technique for the analysis of archived formalin-preserved phytoplankton samples permits retrospective assessment of Emiliania huxleyi communities

The coccolithophores, particularly the species Emiliania huxleyi (Lohmann) Hay & Mohler, account for the bulk of global calcium carbonate production and as such play a fundamental role in global CO2 cycling and the carbonate chemistry of the oceans. To evaluate the response of this functional group to the effects of climate change, we undertook a feasibility study to determine whether a retrospective approach could be used on archived coccolithophore datasets. We demonstrate for the first time a technique for the extraction of E. huxleyi nucleic acids from archived formalin-fixed samples of the long-term Continuous Plankton Recorder. Molecular analysis of a nine year old formalin-fixed sample reveals the presence of a diverse population of E. huxleyi genotypes within a developing coccolithophore bloom. In addition, E. huxleyi sequences were amplified from a number of formalin-fixed samples, the earliest of which was collected in August 1972. This molecular assay promises the possibility of studying global variations in the distribution and genetic make-up of E. huxleyi communities over extensive periods of time. (c) 2008 Elsevier B.V. All rights reserved.