Scavenger assemblages under differing trophic conditions: a case study in the deep Arabian Sea

Baited cameras and traps were deployed at four stations in the deep Arabian Sea to investigate the composition of the necrophagous fauna and to evalua te whether regional differences in trophic conditions are reflected by diff ering scavenger assemblages. The ophidiid fish Barathrites iris, the large lysianassoid amphipod Eurythenes gryllus, the aristeid prawn Plesiopenaeus armatus, and zoarcid fishes of the genus Pachycara were abundant at the bai t at all stations. The ophidiid Holcomycteronus aequatorius, the liparid fi sh Paraliparis sp., and galatheid crabs of the genus Munidopsis occurred in considerable numbers at single sites. Trap catches further contained lysia nassoid amphipods of the genera Paralicella, Abyssorchomene and Paracalliso ma. In contrast to scavenger assemblages of the Atlantic and Pacific Ocean, macrourid fishes were virtually absent at the bait. E. gryllus and B. iris consumed the main proportion of the bait, while consumption was at most mo derate in all other taxa. Feeding strategies of the respective taxa are inf erred from their behavior at the bait and discussed with regard to the prof it that can be drawn from food falls. Differences between stations were pronounced with respect to species domina ting bait consumption. E. gryllus appeared in highest numbers at the bait i n the productive northern and central Arabian Sea where a relatively high a vailability of food items is expected to sustain high population densities. High numbers of B. his in the least productive southern part indicate thei r ability to persist under food-poor conditions and may correspond to a hig h dependency on food falls. E. gryllus and B, iris both occurred in smaller numbers in the particularly productive western Arabian Sea. This may refle ct a reduced dependency on food falls, due to an access to alternative food sources, rather than small population densities. Smaller numbers of E. gry llus and B. iris resulted in slower bait consumption and gave Pachycara spp . the opportunity to contribute considerably to bait consumption. The relat ion between scavenger assemblages and trophic conditions is discussed with respect to results obtained under differing trophic regimes in the Atlantic and Pacific Ocean. (C) 2000 Elsevier Science Ltd. All rights reserved.