Feeding behaviour of deep-sea dwelling holothurians: inferences from a laboratory investigation of shallow fjordic species

An experimental mesocosm was used to investigate the feeding behaviour, particle size selectivity, gut throughput time and dietary selection of two holothurian species, Stichopus tremulus (Gunnerus) and Mesothuria intestinalis (Ascanius). Specimens usually only present at depths > 1000m in the North-eastern Atlantic Ocean were collected from a relatively shallow (< 100 m) cold-water fjordic system in Sweden and maintained in the laboratory. Both species exhibited a similar strategy for retrieving sediment particles from the sediment surface; feeding tentacles were used in a ‘grasping’ motion to pick up sediment particles. The rate at which the feeding tentacles were placed onto the sediment surface, however, differed between species (S. tremulus was three times quicker than M. intestinalis) resulting in a significant difference in gut throughput time. Both species, when offered different sized sediment particles, showed a preference for finer sediment and for nutritionally rich, pigment-enhanced, food patches.