Preservation effects on isotopic signatures in benthic foraminiferal biomass

Autor(en)

Annekatrin Enge, Wolfgang Wanek, Petra Heinz

Abstrakt

Foraminiferal samples for stable isotope analysis are frequently preserved after field collection or during cruises despite the lack of knowledge if and how preservation changes the elemental and stable isotope composition of the protists. Thus, the aim of this study was to investigate the effects of preservation on natural and stable isotope-enriched foraminifera. We tested the following preservation methods on specimens of the benthic foraminifer Ammonia sp. (without surrounding sediment): drying at room temperature, freezing (−25 °C in seawater), ethanol with and without Rose Bengal (RB), and formalin with and without RB. Natural specimens were preserved for 14, 90, and 240 days, while stable isotope-enriched specimens were preserved for 30 days following a pulse-chase feeding experiment. Regardless of type and length, preservation caused a significant loss of carbon (biomass) of up to 42% and lower nitrogen contents in most treatments. Already preservation for 14 days significantly affected δ13C and δ15N signatures, with the strongest shifts caused by freezing at −25 °C in seawater and formalin fixation (with RB). With longer preservation time, the gap between foraminiferal δ13C signatures and the control signal increased for all preservation methods except for 96% ethanol. The observed shifts in the δ13C signatures in the differently preserved foraminifera are in a range of shifts that are found in the signatures of natural foraminifera and are caused by the uptake of various food sources. Applying different preservation methods therefore can bias trophic interpretations based on natural isotope abundances. Preservation of stable isotope-enriched foraminifera in ethanol (with and without RB) resulted in significantly lower carbon uptake estimates, while freezing caused significantly lower nitrogen uptake estimates. Our findings suggest that, if possible, any storage or preservation should be avoided, especially in formalin or at −25 °C with seawater; otherwise storage should be kept as short as possible. Of all tested methods, drying foraminifera at room temperature was the least affecting method with comparatively low variation among replicates. Comparison of biomass, isotope signatures and uptake estimates obtained from differently preserved specimens should be considered carefully, as differences might not be caused naturally, but by alterations of the cytoplasm during preservation.

Organisation(en)

Institut für Paläontologie

Journal

Marine Micropaleontology

Band

144

Seiten

50-59

Anzahl der Seiten

10

ISSN

0377-8398

DOI

https://doi.org/10.1016/j.marmicro.2018.09.002

Publikationsdatum

10-2018

Peer-reviewed

Ja

ÖFOS 2012

106021 Meeresbiologie, 105118 Paläontologie

Schlagwörter

ASJC Scopus Sachgebiete

Oceanography, Palaeontology

Sustainable Development Goals

SDG 14 – Leben unter Wasser

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/63e59b1c-00ee-4107-ba1b-3a07621f630b