SEDIMENT BIOTURBATION BY THE ECHIURAN WORM MAXMUELLERIA-LANKESTERI (HERDMAN) AND ITS CONSEQUENCES FOR RADIONUCLIDE DISPERSAL IN IRISH-SEA SEDIMENTS

Bioturbation by the deep-burrowing echiuran Maxmuelleria lankesteri wa s studied in Loch Sween, Scotland. Results were used to evaluate the a nimal's likely effects on the movement of radionuclides in sediments o f the NE Irish Sea, where the species is also common. Individual burro w openings were monitored by video for up to 23 days. There was no con sistent relationship between the frequencies of sediment intake and ej ection, an anomaly which suggests that the burrow of M. lankesteri has two surface openings rather than one, as believed previously. Sedimen t output was measured by changes in ejecta mound volume and by direct collection of vented material. Both methods gave a value of approximat ely 13 g dry matter . day(-1), of which about 0.8 g (6%) was faecal ma tter. The remainder consisted of non-faecal fluidized sediment, for wh ich concentrations of Th-234 suggested a surface origin. There were no significant differences in particle size composition between burrow e jecta and ambient surface sediment. Sediment ingestion rate was not di rectly measurable, but was estimated at about 1.7 g . day(-1) using a model derived from studies of other marine deposit feeders. Bioturbati on by M. lankesteri seems to result in a short-term redistribution of material (about 13 g . day(-1)) on the sediment surface, with about 0. 9 g . day(-1) incorporated into the burrow lining as faecal pellets. I n the NE Irish Sea, burrows will act as sinks for surface-derived radi onuclides and there is probably little return of deeply-buried materia l to the sediment surface.