CONSUMPTION OF FISHERIES DISCARDS BY BENTHIC SCAVENGERS - UTILIZATIONOF ENERGY SUBSIDIES IN DIFFERENT MARINE HABITATS

1. Man has increased the input of carrion to marine communities worldw ide through the practice of discarding fisheries-derived material. A l arge proportion of discarded material sinks to the sea bed and becomes available to benthic scavengers. Carrion from fisheries discards will subsidize marine food webs, which can sometimes result in the enhance ment of consumer populations. 2. This study examines the benthic scave ngers that feed on fisheries discards in three habitats in the Irish S ea. We investigated the relationship between the abundance of scavenge rs feeding on carrion in terms of numbers of each species and the dens ity of those scavenger species in the surrounding area. 3. Observation s with bailed time-lapse cameras at a site offshore From Anglesey show ed that the hermit crab Pagurus bernhardus was attracted to carrion in greatest abundance and aggregated at densities oi up to 330 m(-2). At Red Wharf Bag. a wider range of species was observed: starfish Asteri as rubens, hermit crabs P. bernhardus, whelks Buccinum undatum and swi mming crabs Liocarcinus spp. There was relatively little scavenging ac tivity at the Walney Island site where the edible crab Cancer pagurus appeared to consume the greatest proportion of the carrion. 4. Numbers of each scavenger species at the bait were only partially related to the background population density of each species at each site. The ra te of consumption of carrion varied between sites and could be related to the abundance of different scavenger species at the bait. 5. Baite d traps were used to investigate those benthic scavengers that were to o small to be observed by time-lapse photography. The traps caught a v ariety of amphipod and isopod species. Some species were habitat-speci fic, whereas others were ubiquitous, but specialized in eating a parti cular type of carrion; for example, Orchomene nanus, which was only ca ught in traps baited with crab. 6. The results demonstrated that the r esponses of scavengers to fisheries discards varied between different habitats. The responses of hermit crabs, P. bernhardus, were particula rly variable, with large aggregations oi. individuals occurring at one site but not at others, despite similar background population densiti es.