Feeding behaviour of Lumbriculus variegatus as an ecological indicator of in situ sediment contamination

Abstract

Previous studies have demonstrated that the feeding behaviour of Lumbriculus variegatus may be significantly inhibited during exposure to toxic substances. The potential use of an in situ sediment bioassay, using L.variegatus post-exposure feeding inhibition as an endpoint, was investigated. The bioassay consisted of exposing animals in the field for a six-day exposure period and feeding rates were measured immediately afterwards over a twenty-four hour post-exposure period. The bioassay methodology developed in the laboratory produced a consistent baseline response that was reliable and repeatable.

Endpoint sensitivity was demonstrated under laboratory conditions, where bioassay organisms exhibited delayed recovery from feeding inhibition after previous exposure to sediment-associated contaminants. The apparent insensitivity of the bioassay to sediment-associated metals means that the technique should only be used as part of a suite of bioassays that employ representative deposit feeders. The ecological relevance of the bioassay endpoint was also demonstrated by comparing short-term measures of post-exposure feeding inhibition with the longer-term effects of a toxicant on L.variegatus populations.

The bioassay methodology was successfully adapted for in situ use. Post-exposure feeding inhibition was detected at contaminated field sites. However, the consistent baseline response produced in the laboratory could not be replicated during deployments of the bioassay at upstream (“clean”) field sites. Increased environmental “noise” may have been a result of a number of confounding factors that could limit the sensitivity of the bioassay endpoint if not adequately controlled. Despite the above concerns, the in situ bioassay is suggested to represent a useful tool, which uses a more realistic field exposure scenario to investigate the effects of sediment-associated toxicants with an important functional component of aquatic ecosystems.