Estimates of carbon turnover rates in the sea cucumber Apostichopus japonicus (Selenka) using stable isotope analysis: The role of metabolism and growth

Abstract

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. © Inter-Research 2012.