Feeding, agonistic and cooperative behavioural responses of shallow-water benthic marine scavengers

Baited remote underwater video station (BRUVS) investigations of benthic scavenging by fish and invertebrates were conducted in an Irish sea lough. Mackerel (Scomber scombrus) baits were deployed under natural light during the day and under dim red light at night. Ethograms for feeding mechanisms and agonistic behaviours were established for four abundant scavengers (two crabs: the harbour crab Liocarcinus depurator, and the European green crab Carcinus maenas; two fish: the shanny Lipophrys pholis, and the small-spotted catshark Scyliorhinus canicula). Crabs' feeding mechanisms were similar, with differences reflecting their morphologies. Feeding bouts lasted minutes/tens of minutes. Intraspecific agonistic responses were mild and did not result in mutilation or mortality. Feeding mechanisms on macerated baits focussed on 'chewing' (combined use of chelipeds and mouthparts to feed continuously); agonistic behaviour was reduced, especially at night when balls of crabs showed 'cooperative feeding'. Fish feeding bouts lasted for a few seconds in all cases. Shannies showed anticipatory agonistic behaviour (bait 'guarding' and 'patrolling' by large shannies) before bait maceration. Catsharks exhibited no intraspecific agonistic behaviour but removed large bait morsels by 'biting', 'chewing' and 'spinning'. The common prawns Palaemon serratus only scavenged at night and were invisible to other scavengers; they showed no agonistic behaviours. Kleptoparasitism amongst the scavenger guild was common but intra-community predation was extremely rare. Phoretic feeding on bait scraps by red-speckled anemones (Anthopleura ballii) attached to the carapaces of the edible crab Cancer pagurus was observed.