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 was studied in Loch Sween, Scotland. Results were used to evaluate the animal's likely effects on the movement of radionuclides in sediments of the NE Irish Sea, where the species is also common. Individual burrow openings were monitored by video for up to 23 days. There was no consistent relationship between the frequencies of sediment intake and ejection, an anomaly which suggests that the burrow of M. lankesteri has two surface openings rather than one, as believed previously. Sediment output was measured by changes in ejecta mound volume and by direct collection of vented material. Both methods gave a value of approximately 13 g dry matter . day(-1), of which about 0.8 g (6%) was faecal matter. The remainder consisted of non-faecal fluidized sediment, for which concentrations of Th-234 suggested a surface origin. There were no significant differences in particle size composition between burrow ejecta and ambient surface sediment. Sediment ingestion rate was not directly measurable, but was estimated at about 1.7 g . day(-1) using a model derived from studies of other marine deposit feeders. Bioturbation 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. In the NE Irish Sea, burrows will act as sinks for surface-derived radionuclides and there is probably little return of deeply-buried material to the sediment surface.