Assimilation Dynamics of Different Diet Sources by the Sea Cucumber Holothuria scabra, with Evidence from Stable Isotope Signature

Abstract

The sea cucumber Holothuria scabra has a high commercial value and a great potential to be cultivated. A thorough feeding strategy is needed to overcome juvenile rearing technique constraints. Stable isotope analysis can be used for determining diet sources of sea cucumbers that play a role as deposit feeders. This study aims to determine suitable diet sources and elucidate the potential of organic matter assimilation of H. scabra by combining three different mixed diets including 10% seagrass Enhalus acoroides bulk, 45% grass Pennisetum purpureum and 45% of cow feces (diet A); 20% seagrass E. acoroides, 40% grass P. purpureum and 40% of cow feces (diet B) and 33% seagrass E. acoroides, 33% grass P. purpureum and 33% cow feces (diet C) and identifying the fecal pellet isotopic properties and compare it to the diet sources and the surrounding sediment. Stable isotope signature of H. scabra and its prospected diet sources, altogether with sediments and fecal pellets were plotted in a conservative bi-plot δ13C and δ15N. The isotopic value of fecal pellets and diet sources indicate a low assimilation rate, the organic matter contained in the sediment is similar to that of the diet sources. Sea cucumber feeds the bulk of the sediment and the detritus of the diet sources and then assimilates the organic matter as soon as the bulk enters the intestine. Due to the low assimilation rates, we suggest for the mariculture of H. scabra that the food should be homogenised and then mixed into the sediment, where the sea cucumber is cultured.