RESOURCE UTILIZATION BY A SEDENTARY SURFACE DEPOSIT FEEDER, THE ECHIURAN WORM MAXMUELLERIA-LANKESTERI

The feeding behaviour of the shallow-water bonelliid echiuran Maxmuelleria lankesteri is described, based on underwater video recordings made in Loch Sween, Argyll, Scotland. We compare the observed utilization of the sediment surface with the systematic grazing pattern inferred for abyssal echiurans from stellate proboscis traces photographed on the deep-sea floor. M. lankesteri feeds by skimming off the sediment surface during the linear extension of the proboscis from the burrow opening. Successive proboscis extensions did not follow a regular clockwise or anticlockwise path around the burrow opening. The frequency distribution of displacement angles between successive extensions did not differ significantly from random. There was no significant tendency for the proboscis to 'follow-up' a successful feed by extending in a similar direction the next time, or for the proboscis to avoid a sector in which it had previously been disturbed. This unresponsiveness was shown irrespective of the time elapsed since the preceding extension. The orientation of the proboscis also showed no significant relationship to the direction of water flow. There was usually little or no overlap of proboscis feeding strokes on individual nights, but 1 individual which fed on 9 consecutive nights re-used a significantly greater proportion of the total area grazed than would be expected if feeding strokes were made randomly. The feeding behaviour of M. lankesteri differs from the pattern attributed to related deep-sea forms in the lack of a systematic proboscis trajectory and in the willingness to re-use previously grazed areas. These differences, if real, may correlate with the trophic status of the habitat. The ability to concentrate feeding effort in specific areas may enable a sedentary deposit-feeder to sequester ephemeral or patchy food resources by 'caching' material within the burrow.