Preservation methods alter stable isotope values in gelatinous zooplankton: implications for interpreting trophic ecology

Abstract

JellyWsh are increasingly topical within studies of marine food webs. Stable isotope analysis represents a valuable technique to unravel the complex trophic role of these long-overlooked species. In other taxa, sample preservation has been shown to alter the isotopic values of species under consideration, potentially leading to misinterpretation of trophic ecology. To identify potential preservation eVects in jellyWsh, we collected Aurelia aurita from Strangford Lough (54 o 22Ј44.73ЉN, 5 o 32Ј53.44ЉW) during May 2009 and processed them using three diVerent methods prior to isotopic analysis (unpreserved, frozen and preserved in ethanol). A distinct preservation eVect was found on 15 N values: furthermore, preservation also inXuenced the positive allometric relationship between individual size and 15 N values. Conversely, 13 C values remained consistent between the three preservation methods, conXicting with previous Wndings for other invertebrate, Wsh and mammalian species. These Wndings have implications for incorporation of jellyWsh into marine food webs and remote sampling regimes where preservation of samples is unavoidable.

Jellyfish biochemical composition: importance of standardised sample processing

“…Therefore, even partial changes in the total AA pool during sample preparation can have a significant impact on the δ 15 N composition of jellyfish tissue. Previous studies revealed that preservation methods and processing might modify the stable isotope composition of the samples (Carabel et al 2009, Fleming et al 2011. It is important to emphasize that, in our study, the impact of preservation methods on jellyfish biochemical composition was not tested.…”

“…Stable isotope composition should be determined in freeze-dried jellyfish, especially in the case of δ 15 N. Determining the δ 15 N of ovendried jellyfish material might lead to an incorrect estimation of its trophic position. It should be noted that preservation of samples in ethanol (Carabel et al 2009) or freezing jellyfish for several months (Fleming et al 2011) may affect the stable N composition of gelatinous organisms, and therefore analysis of fresh samples is highly recommended. When organic matter from different sources shares similar C and N isotopic composition, δ 34 S can be used as an additional element to determine its source.…”

“…Several studies demonstrated that freezing, the most commonly used method for sample preservation, does not affect stable nitrogen and carbon isotopes values in fish, octopus, anemone, bivalves, kelp and algae (Kaehler & Pakhomov 2001, Carabel et al 2009). However, the opposite was suggested by Fleming et al (2011) in the case of gelatinous plankton: while freezing did not affect δ 13 C, the prolonged storage of frozen Aurelia aurita medusae resulted in the enrichment in 15 N. Preservation in ethanol affected the δ 15 N in some species of invertebrates (Carabel et al 2009, Fleming et al 2011, while there was no significant change in nitrogen isotope ratio in fish, octopus and kelp (Kaehler & Pakhomov 2001). In addition to preservation techniques, sample processing might also alter sample stable isotope ratios.…”

Scyphozoan jellyfish provide short-term reproductive habitat for hyperiid amphipods in a temperate near-shore environment

“…A. aurita, C. lamarckii and C. capillata were weighed and measured (wet mass: ±1 g; bell diameter: ±1 cm), dried at 60°C (Fleming et al 2011) then desiccated for 48 h to prevent the absorption of water vapour during cooling. Desiccated samples were then ground to a fine powder using an agate pestle and mortar in preparation for stable isotope analysis (SIA).…”

Bases morfo-funcionais da alimentação e o papel trófico de iLychnorhiza lucerna (Scyphozoa, Rhizostomeae)

“…Some pre-analytical factors can affect δ 15 N and δ 13 C values. For jellyfish, processing methods still need to be standardized (Fleming et al 2011). The widespread preservation method of freezing can increase δ 15 N values of jellyfish (Fleming et al 2011), whereas for fish, octopus, and kelp samples, no effect of freezing was found (Kaehler & Pakhomov 2001).…”