The use of free-living nematodes as a bioassay for estuarine sediments

Abstract

A bioassay technique using free-living nematodes has been developed to assess the environmental quality of estuarine sediments. Nematodes offer the advantages of (a) generally being the most abundant metazoan in sediments; (b) having short life histories and no pelagic larvae; and (c) being relatively easy to maintain in laboratory culture. Small individual body size and rapid generation time (two weeks) render nematodes especially useful in evaluating effects of potential toxicants on populations, rather than on single individuals. The bioassay technique was developed using two species, Chromadorina germanisa and Diplolaimella punicea, and sediments from the Hudson-Raritan estuarine area. The life histories and feeding habits of both species are known. Test sediments were taken from eight stations that represent a gradient from lightly to heavily impacted. Concentrations of potential toxicants measured in these sediments included polychlorinated hydrocarbons, polynuclear aromatic hydrocarbons, and heavy metals. Control sediments, taken from 100 km distant, were almost totally toxicant-free. Nematodes were incubated in the dark at 25°C for two weeks at 1:1 and 1:10 concentrations (volume/volume) of sediments prepared with sterile sea water. Food consisted of bacteria from nematode stock cultures. Intrinsic rate of natural increase ( r) of the nematodes was used as the indicator of sediment quality; r has units (daily increase in number of generations), is easily computed, and can be treated statistically. Both species grew better in control and other sediments containing low concentrations of PCBs, PAHs, and heavy metals. In sediments having TIF PCB and PAH concentrations (ppb) of more than 270 and 8700, respectively, population growth of both species tended to be less than half that found at lower concentrations. Significant inverse correlations between r and toxicant concentration occurred at 1:1 sediment-water concentrations. At 1:10 concentrations the correlations remained negative, but not at the 0·05 level of significance. Use of the nematodes Chromadorina germanica and Diplolaimella punicea offers a quick, easy and statistically testable means of assessing the quality of marine sediments on populations, rather than single individuals, of marine benthic invertebrates.