Shifting feeding behaviour of deep-sea buccinid gastropods at natural and simulated food falls

The deep sea is a low food input environment, hence large food falls from the surface waters are important in supporting a wealth of scavenging deep-sea fauna. The probability of observing such events is very low, due to their unpredictable and short-lived nature. The video system of a cabled observatory installed within a cold seep clam field in Sagami Bay (1100 m depth; Central Japan) recorded a rare event. We observed a fish dying directly in front of the camera and being immediately perceived and preyed upon by Buccinum yoroianum (Neogastropoda: Buccinidae), while still alive. Up to 76 large snails responded to the fish and consumed the carcass within similar to 8 h, with no intervention by decapod crustaceans. There was only small participation of eelpouts (Zoarcidae). For comparison, we report on supplementary findings from a different area and depth of the Pacific Ocean. These observations were recorded by a baited camera lander which simulated a food fall. Within 6 h, the buccinid Tacita zenkevitchi aggregated on the bait, competing with fishes. These observations confirm that deep-sea buccinids can shift their feeding behaviour between active predation and scavenging. Our perception, however, seems conditioned by the observational methodology we use: buccinids may appear as scavengers when using photography (e. g. by baited landers) producing single snapshots in time, or as predators when observed in a natural setting and video-taped continuously with a cabled observatory.