Stable isotope and fatty acid tracers in energy and nutrient studies of jellyfish: a review

Abstract

Studies of the trophic ecology of gelatinous zooplankton have predominantly employed gut content analyses and grazing experiments. These approaches record only what is consumed rather than what is assimilated by the jellyfish, only provide evidence of recent feeding, and unless digestion rates of different prey are known, may provide biased estimates of the relative importance of different prey to jellyfish diets. Biochemical tracers, such as stable isotopes and fatty acids, offer several advantages because they differentiate between what is assimilated and what is simply ingested, they provide an analysis of diet that is integrated over time, and may be useful for identifying contributions from sources (e.g., bacteria) that cannot be achieved using gut content approaches. Stable isotope analysis has become more rigorous through recent advances that provide: (1) signature determination of microscopic organisms such as microalgae, (2) analysis of dissolved organic carbon, and (3) improved quantification of relative source contributions. The limitation that natural tracer techniques require different dietary sources to have unique signatures can potentially be overcome using pulse-chase isotope enrichment experiments. Trophic studies of gelatinous zooplankton would benefit by integrating several approaches. For example, gut content analyses may be used to identify potential dietary sources. Stable isotopes could then be used to determine which sources are assimilated and modeling could be used to quantify the contribution of different sources to the diet. Analysis of fatty acid profiles could be used to identify contributions of bacterioplankton to the diet and, potentially, to provide an alternative means of identifying dietary sources in situations where the isotopic signatures of different potential dietary sources overlap. In this review, we outline the application, advantages, and limitations of gut content analyses and stable isotope and fatty acid tracer techniques and discuss the benefits of using an integrated approach toward studies of the trophic ecology of gelatinous zooplankton.

Trophic effects of fishing southern rock lobster Jasus edwardsii shown by combined fatty acid and stable isotope analyses

“…For nitrogen, fractionation is larger and on average 3.5 ‰ per trophic level (McCutchan et al 2003, Waddington & MacArthur 2008. Fractionation rates can vary between species with such issues as diet type (Vanderklift & Ponsard 2003) and dietary studies are required to confirm the fractionation rates of individual species (Pitt et al 2009). As this was beyond the scope of the present study, the sensitivity of the IsoSource mixing model was run for each species using a range of fractionation rates for carbon and nitrogen.…”

“…For example, the isotopic separation of algal species, or the detection of a proportional change to lobster diet (in response to changes in lobster density) is difficult in situations where lobsters are consuming a wide range of food items from differing trophic levels. δ 15 N values can also be influenced by diet quality (Vander Zanden & Rasmussen 2001) and can vary between the tissue types of the target species (Pitt et al 2009). Manipulative feeding trials were beyond the scope of the present study but may help to calibrate the feeding relationships indicated by stable isotopes in the present context.…”

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

“…ctenophores) are diYcult to quantify and identify owing to fast deterioration in the oral arms and gut cavity (Båmstedt and Martinussen 2000;Ishii and Tanaka 2001;Pitt et al 2009); (2) once out of the water, gelatinous samples rapidly lose physical integrity; (3) sampling at remote sites or on research cruises of extended duration can limit access to suitable processing/analytical equipment and jellyWsh collected in the Weld are typically preserved by freezing or storage in ethanol (EtOH) (Hobson et al 1997). Preservation methods employed prior to stable isotope analysis (SIA) have been shown to alter isotopic composition in a range of marine taxa ranging from algae (Kaehler and Pakhomov 2001;Carabel et al 2009) through to invertebrates (Bosley and Wainwright 1999;Kaehler and Pakhomov 2001;Carabel et al 2009) and higher vertebrates (Bosley and Wainwright 1999;Kaehler and Pakhomov 2001).…”

Role of winds and tides in timing of beach strandings, occurrence, and significance of swarms of the jellyfish Crambione mastigophora Mass 1903 (Scyphozoa: Rhizostomeae: Catostylidae) in north-western Australia

“…However, although we were able to provide some data on the biomass of stranded jellyfish that this is only a reflection of the total biomass as we do not know what percentage of the population is stranded at any one time. Other jellyfish species which undergo swarms have been shown to be important in delivering significant quantities of organic matter into coastal food webs (Pitt et al, 2009b;West et al, 2009). Kramp (1961) records C. mastigophora as reaching 400 mm in diameter, but our specimens were almost all less than half this size.…”