Stable isotope analysis is increasingly being used to determine the trophic relationships of aquatic ecosystems. Most ecological and biological conclusions from isotope analysis are based on the assumption that the tissues of the respective consumers are in equilibrium with the potential food sources. Such an assumption, however, is not always validated in individual field studies. Hence, knowledge of the stable isotope turnover rates for the experimental organisms is fundamental for interpreting isotopic data. In this study, the carbon isotopic turnover rates for body walls and intestines of sea cucumbers Apostichopus japonicus (Selenka) of different sizes were investigated. The carbon isotopic turnover rate for the intestine was found to be faster than that for the body wall. The carbon stable isotope turnover rate decreased with an increase in body size, owing to the decrease in the metabolic activities of the larger individuals. Metabolism, rather than growth, was the principal driver of carbon stable isotope turnover, contributing 80 to 90% of the turnover for the intestine and 60 to 75% for the body wall. Analysis of the relationship between carbon replacement and the metabolism of sea cucumbers showed that the half-lives of carbon isotope replacement for both intestine and body wall were significantly related to physiological activities in terms of the oxygen consumption rates and food ingestion rates of the sea cucumbers. Our findings suggested that differences in turnover rates between various species and tissues should be considered when using stable isotopes in ecological studies. It is proposed that further development of isotope mixing models is needed and that these models should integrate isotope turnover for specific species or tissues.
KEY WORDS: Sea cucumber · Apostichopus japonicus (Selenka) · Carbon turnover · Stable isotope · Metabolism
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 457: [101][102][103][104][105][106][107][108][109][110][111][112] 2012 tern (Tieszen et al. 1983, Peterson & Fry 1987, McCutchan et al. 2003. Carbon stable isotope, which typically discriminates with the delta value (δ) of 1 ‰ for each trophic level (Peterson & Fry 1987), is often used to quantify food assimilation, providing the technical measure for analyzing consumers long-term food utilization (Peterson et al. 1985, Kurata et al. 2001, Yokoyama et al. 2005, Gao et al. 2006, Kharlamenko et al. 2008. These studies and their conclusions are based on the assumption that tissues of consumers are in isotopic equilibrium with their diet (Post 2002, Gao et al. 2006. However, this may not necessarily be true, since the carbon isotopic ratios of the food items absorbed by the consumer are always dynamic. This is due to the different mechanisms of carbon fixation between primary producers, the seasonality of food availability and the movement or migration of predators, as well as the difference in the physiological characteristics of various species . When t...