The diverse origin of organic matter makes it difcult to discriminate what the most important food sources are in the animal diet and to quantitatively estimate their proportions. The different food sources contribute to an important detrital organic matter pool (Pocklington and Tan 1987; Mann 1988) and may be used differently by different animals due to their digestibility or because of hydrology that inuences their production and availability to consumers (Schwinghamer et al. 1983; Monbet 1992). Studies of the feeding relationships of deep-sea organisms are very limited and have concentrated primarily on gut-content data that display substantial limitations (Polunin et al. 2001). For example, gut contents reect diets at particular points in time and space, and severely neglect certain types of dietary materials such as gelatinous plankton and detritus that may nevertheless be very important in the sustenance of marine food webs (Polunin et al. 2001). Other limitations include problems associated with the voiding of gut contents upon capture and the very sporadic feeding of many carnivorous species. Furthermore, many animals crush or grind their food, such that the identication of prey becomes very difcult, and it is not often clear which components of their diets are actually assimilated, particularly when refractory or amorphous foods are ingested (Pinnegar and Polunin 2000). The use of stable nitrogen and carbon isotopes for the study of trophic interactions is now common in aquatic ecosystems (Pinnegar and Polunin 2000) also in the deep sea (Schubert and Calvert 2001; Bosley et al. 2004; Mohtadi et al. 2005; Levesque et al. 2006; Usui et al. 2006).