Feeding relationships in Mediterranean bathyal assemblages elucidated by carbon and nitrogen stable-isotope data

Fishes and invertebrates were collected from the continental slope southwest of the Balearic Islands, Mediterranean, in October 1996 and May 1998 from 3 faunally-distinct depth zones: 200 to 800 m (upper slope), 800 to 1425 m (middle slope) and 1425 to 1800 m (lower slope). Differences in 15 N and 13 C between October 1996 and May 1998 were observed only in the crustaceans Aristeus antennatus and Nematocarcinus exilis. There were few differences among depths in 15 N or 13 C of benthic fishes or crustaceans: the shrimps A. antennatus and Acanthephyra eximia showed higher 15 N values at greater depth, and 13 C values of the fishes Alepocephalus rostratus (Alepocephalidae) and Coelorhynchus coelorhynchus (Macrouridae) also tended to increase with increasing depth. Differences in plankton and suprabenthos were also observed among zones (at depth, greater 15 N values of gelatinous plankton, calanoid copepods and peracarids were recorded, along with smaller 13 C values of gelatinous plankton and peracarids). These are attributed to a microbially-mediated increase in 15 N and a reduction in 13 C of the particulate material remaining after preferential utilization of labile organic matter in the stable and relatively high (13C) temperature of the Mediterranean water column. Strong positive correlations between 15 N and 13 C data for plankton, fishes and crustaceans indicated a single primary source material for these communities, which is attributed to marine snow.