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

Fishes and invertebrates were collected from the continental slope southwes t 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 delta N-15 and delta C-13 between October 1996 and May 1998 were observed only in the crustaceans Aristeus antennatus and Nematocarcinus exilis. There were few differences among depths in delta N-15 or VC of benthic fishes or crustacea ns: the shrimps A. antennatus and Acanthephyra eximia showed higher delta N -15 values at greater depth, and delta C-13 values of the fishes Alepocepha lus rostratus (Alepocephalidae) and Coelorhynchus coelorhynchus (Macrourida e) also tended to increase with increasing depth. Differences in plankton a nd suprabenthos were also observed among zones (at depth, greater VN values of gelatinous plankton, calanoid copepods and peracarids were recorded, al ong with smaller delta C-13 values of gelatinous plankton and peracarids). These are attributed to a microbially-mediated increase in delta N-15 and a reduction in delta C-13 of the particulate material remaining after prefer ential utilization of labile organic matter in the stable and relatively hi gh (13 degreesC) temperature of the Mediterranean water column. Strong posi tive correlations between delta N-15 and delta C-13 data for plankton, fish es and crustaceans indicated a single primary source material for these com munities, which is attributed to marine snow.