Trophic ecology of three echinoderms in deep waters of the Weddell Sea (Antarctica)

Abstract

n the Southern Ocean, the trophic ecology of deep-sea communities is probably one of the most neglected fields in the discipline. In the present study, the trophic position and energy storage-mobilization of 3 different deep-sea echinoderms living in the Weddell Sea (around 1500 m depth) were investigated with indirect tools (i.e. stable isotopes, carbohydrate-lipid-protein balance, and free fatty acid [FFA] contents). The stalked crinoid Dumetocrinus antarcticus, the holothurian Rhipidothuria racovitzai, and the ophiuroid Ophiura carinifera were sampled in spring 2003 during a Polarstern cruise. We found that stable isotopes were in line with previous results of other species (δ13C ranging from -24.3‰ to -26.5‰; δ15N ranging from 6.8‰ to 7.9‰), showing similarities in the trophic position of the 3 echinoderms. The capability of these 3 organisms to store energy is conspicuous and different, e.g. from 18 to 45% of the organic matter (OM) consists of lipids. The capability to mobilize energy in the form of carbohydrates and FFAs among species was also very different (e.g. biomolecules ranging from 9 to 22 µg carbohydrates mgOM-1 and from 4 to 39 µg FFA mgOM-1). It is suggested that even if the trophic level is similar in the 3 echinoderms, the strategies to invest the energy inputs in these deep-sea organisms in polar environments may be quite different.