Correction of the isotopic composition (δ13C and δ15N) of preserved Baltic and North Sea macrozoobenthos and their trophic interactions

Abstract

To better understand food webs and the trophic relationships of marine animals studied by means of preserved material requires knowledge of the effects of preservation on the organic materials of interest. We examined the effects of formalin and ethanol preservation on the stable isotope values of carbon and nitrogen in the bivalves Mya arenaria and Tellina fabula and in the polychaetes Magelona spp. and Hediste diversicolor. Samples of these organisms were collected in the southern North Sea and the southern Baltic Sea, and were preserved with formalin, ethanol, and by freezing. The stable isotope patterns of carbon and nitrogen in the chemically preserved samples were related to those in the frozen samples. The influence of different preservation methods on the stable isotope composition was analyzed using a correction model that is independent of the molar C:N ratio. For most samples from the North Sea, significant correction factors were obtained. In contrast, none of the samples from the Baltic Sea were impacted by the preservatives with respect to their δ 15 N values, and, for H. diversicolor, also with respect to the δ 13 C values. In these cases, corrections of the δ 13 C and the δ 15 N values were not necessary. Quantitative metrics using a phenotype-based approach were computed to characterize aspects of the trophic structure of the benthic community. Phenotypic clustering in isotopic diversity indicates no competition for food between the dominant species. Our results indicate that a representative dominant mollusk and polychaete species have a higher trophic position in the Baltic Sea than in the North Sea.

Effects of preservation methodology on stable isotope compositions of sea stars

“…8,[12][13][14][15][16] The influence of preservation methodology on stable isotope ratios has also been investigated in various other taxa such as elasmobranchs, 17,18 chelonians, 19 birds, 20 marine mammals, 21 terrestrial mammals, 22 and even photosynthetic organisms. 8,11,23 The influence of preservation methods on stable isotope ratios has also been investigated in several invertebrate taxa such as cnidarians, 11,24 mollusks, 8,10,11,25,26 polychaetes, 10,26 sipunculids, 10 and aquatic 12,14,27 and terrestrial arthropods. 28,29 Nevertheless, the influence of preservation method on stable isotope ratios has been poorly investigated for several taxa.…”

Stable isotope analysis in food web research: Systematic review and a vision for the future for the Baltic Sea macro-region

“…A second disconnect concerns “users” of existing SIA methodology versus “developers” at the technological forefront of the field. The Baltic Sea SIA field has included foundation work on the bioaccumulation of contaminants (Broman et al 1992 ; Rolff et al 1993 ), the development of simultaneous low biomass CNS analysis (Hansen et al 2009 ), and the development of correction factors for isotope data derived from preserved macrozoobenthos samples (Umbricht et al 2018 ) and lipid content (Kiljunen et al 2006 ). Nevertheless, the lag between global and Baltic BSIA and CSIA publication timelines as well as the limited number of highly cited SIA method and foundation papers points to a partial disconnect between the macro-regional and global SIA community.…”