Trophic strategies in carnivorous fishes: their significance in energy transfer in the deep-sea benthic ecosystem (Meriadzek Terrace — Bay of Biscay)

Abstract

Trophic relationships between fish species have been analyzed as a contribution to the construction of an energy transfer model between various groups in the benthic ecosystem of Meriadzek Terrace, located at 170 miles off the west French coast at a depth of 2100m. Attention was given to the carnivorous megafaunal compartment. The importance of the carnivore megafaunal biomass and its part in energy transfer is still unresolved. On the Meriadzek Terrace, numerous Chondrichthyes (sharks and chimeroids) were frequently observed from the manned submersible Cyana or by baited camera; their biomass appears to be exceptionally large. Results of a photographic survey conducted using the unmanned free vehicle Epaulard have given estimates of 22 per 10 4m 2 of teleost fishes (belonging to 8 different families and one suborder) but included no Chondrichthyes (except one specimen of Rajidae). From baited camera observations, however, we conclude that carcasses falling to the bottom on the Terrace are exploited only by selacians as the bait was never seen to be eaten by macrourids, morids or synaphobranchids although they always attended the baits before the arrival of large scavengers. Trophic specialization strategies occur in this deep-sea ecosystem and our further studies on the energy transfer model for the Meriadzek Terrace will differentiate between strategies exploiting two sources of organic input to the bottom environment: organic particles and large carcasses. In one case, carbon transfer is via the whole benthic food web in which each link is specified by size and trophic behaviour. This pathway ends in the carnivorous megafaunal compartment, which includes benthic fishes, consumers of the local epibenthic and sometimes inbenthic, macro- and megafauna. The second pathway originates with carcass falls, and carbon transfer is direct to the benthopelagic scavengers observed frequently at the Meriadzek Terrace.