Utilization of different macroalgae by sea cucumber Apostichopus japonicus revealed by carbon stable isotope analysis

Abstract

Understanding the feeding habit of sea cucumber Apostichopus japonicus (Selenka) is crucial for improving aquaculture techniques of this commercially important species. In the present study, carbon stable isotopes were used as trophic tracers to investigate the uptake of different macroalgae, including brown alga Sargassum muticum, red alga Gracilaria lemaneiformis and green alga Ulva lactuca by A. japonicus. A 70 d experiment was conducted to examine the carbon isotopic signatures of A. japonicus feeding on 6 different types of diets containing either pure powder of a single alga species or mixtures of 2 algae species. After the feeding trial, carbon isotope ratios (δ13C) of A. japonicus showed significant changes and reflected the isotopic compositions of corresponding diets. An isotope mixing model revealed the dietary preferences of A. japonicus between the 3 species of macroalgae, suggesting that green alga U. lactuca was the preferentially utilized food source of A. japonicus, followed by brown alga S. muticum. A. japonicus tended to reject red alga G. lemaneiformis in the presence of multiple macroalgae choices. Moreover, the specific growth rates of A. japonicus fed on S. muticum and U. lactuca were similar, but were both significantly higher than those fed on G. lemaneiformis, indicating the direct link between the feeding preferences and growth performance of A. japonicus.