An experimental study on variations in stable carbon and nitrogen isotope fractionation during growth of Mysis mixta and Neomysis integer

Abstract

The trophic isotope fractionation of mysids, in response to a change in the isotopic composition in their diet, was examined in the laboratory. Field-caught Mysis mixta and Neomysis integer had similar δ13C values, ranging between -23.1 and -21.5‰. They also had similar δ15N values, and for both species, this value increased with body size. Experimental starvation did not change the isotopic composition. To test for metabolic fractionation of isotopes, the mysids were fed different diets, newly hatched Artemia and detrital Enteromorpha. The isotopic composition was monitored in abdominal muscle tissue, exoskeleton, and feces over 12 weeks. The δ13C composition in muscle tissue had not reached an isotopic equilibrium with the diet at the end of the experiment, while the exoskeleton came into equilibrium with the food in 2-3 weeks. Muscle was enriched in 15N relatively to the food, +3.6‰ for Artemia and +2.7‰ for Enteromorpha. The isotopic composition in muscle, exuviae, and feces may form a basis for diet reconstruction of mysids. The feces δ13C and δ15N values mirror the diet over the last few hours, exuviae δ13C values represent nutrients metabolized 2-3 weeks ago, and muscle tissue integrates the isotopic signal over a relatively long period.

Altered complementary feeding strategies of the consumers Hydrobia ulvae and Idotea emarginata via passive selectivity

“…When the 13 C and 15 N values for the animals are compared to the isotope composition of their faecal pellets, it is apparent that substantial 15 N-and 13 Caccumulation occurred in the faecal pellets indicating a strong fractionation towards the lighter isotopes during gastrointestinal assimilation. Gorokhova and Hansson (1999) reported similar results for mysid shrimps, pointing at an accumulation of the heavy isotopes 13 C and 15 N in their faeces. Another possible explanation for the high accumulation of 15 N and 13 C could be the result of diVerential digestion, e.g.…”

“…In general, gastrointestinal assimilation is considered to be the Wrst step in trophic fractionation (Gorokhova and Hansson 1999) and isotopic composition of faecal material therefore can provide valuable dietary information which would otherwise be overlooked.…”

“…However, diVerences in isotope discrimination are known to occur between algal groups and species (Burkhardt et al 1999;Needoba et al 2003) and studies on natural stable isotope signatures of metazoans have shown that fractionation can be variable as well as species-speciWc (Macko et al 1982;Vander Zanden and Rasmussen 2001;Post 2002;Aberle and Malzahn 2007). Possible explanations for species-speciWc discrimination of heavier isotopes include diVerences in metabolic processes (assimilation, excretion), diVerent levels of isotope enrichment, the diets' and consumers' nutrient content as well as the degree of starvation (Gorokhova and Hansson 1999;Adams and Sterner 2000;Vanderklift and Ponsard 2003). Our results suggest that the gastropod H. ulvae discriminated against the heavier isotopes more strongly than the isopod I. emarginata, thus providing further support for species-speciWc fractionation processes (Vander Zanden and Rasmussen 2001;Post 2002).…”

Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter

“…This pattern indicates a gradual shift in the diet with increasing size and suggests a trend towards increasing carnivory with maturity. Relationships between body length and stable isotopic signatures have already been found for mysids (Gorokhova and Hansson 1999;Branstrator et al 2000;Lesutiene et al 2007), crabs (Dittel et al 2006) and fish (Renones et al 2002;Melville and Connolly 2003;Quan et al 2007). The significant changes in stable isotopic signatures with increasing size are often attributable to ontogenetic diet shifting of animals (Branstrator et al 2000;Renones et al 2002;Quan et al 2007;Lesutiene et al 2007).…”

Mussel isotope signature as indicator of nutrient pollution in a freshwater eutrophic lake: species, spatial, and seasonal variability

“…1 48 h). Adductor muscle tissue was used in this study as muscle tissue has low turnover rates (Gorokhova and Hansson 1999) and is therefore more representative of a time-integrated diet. The tissues were then ground to a fine powder with a mortar and pestle and then stored in a desiccator with a silica gel desiccant for subsequent stable isotope analysis.…”