Rapid treatment of vessels fouled with an invasive polychaete, Sabella spallanzanii, using a floating dock and chlorine as a biocide.

Chlorine solution was added to the water encapsulated within a proprietary 'floating dock' to treat a vessel infested with the invasive polychaete Sabella spallanzanii. The chlorine was added as sodium dichloroisocyanurate ('dichlor') at an initial concentration of 200 mg l(-1) of free available chlorine (FAC). This concentration killed 99% of S. spallanzanii in their tubes during a 4-h exposure in laboratory tests (EC99 160 mg FAC l(-1)). The concentration of FAC in the floating dock declined to ~50 mg l(-1) after 4 h and < 10 mg l(-1) after 16 h. Residual FAC was neutralised with thiosulphate at completion of exposure. A sample of 30 S. spallanzanii individuals collected from the hull after treatment all showed morphological damage and 28 showed no response to touch. Re-examination of the hull after 6 d found no live worms or other fouling organisms. This method provides a cost-effective, rapid means of treating hull fouling.

Factors affecting the distribution of benthic macrofauna in estuaries contaminated by urban runoff.

Contaminants derived from urban runoff have been shown to accumulate in estuarine sediments, reaching concentrations potentially capable of causing biological effects. Demonstration of effects, however, is difficult due to strong natural environmental gradients and the effects of past or present point-sources of contamination. We used multivariate methods to test two hypotheses relating to the effects of urban-derived contaminants on estuarine benthic communities. First, that patterns of distribution and abundance of benthic invertebrates in two urbanised estuaries would be different from those in two non-urbanised estuaries. Second, that the distributions of benthic invertebrates within and among the four estuaries would be related to those of urban-derived contaminants. Concentrations of contaminants were larger in estuaries with urbanised catchments and concentrations of Cu, Pb, Zn and DDT in some samples exceeded those at which biological effects may be expected to appear. Tests of differences in composition of benthic communities among estuaries showed that the two urban estuaries were not significantly different, but that they differed from both rural estuaries, which also differed from each other. Distributions of benthic invertebrates were significantly related to those of environmental variables, and were ordinated along axes that correlated with both natural environmental variables (nature of the sediment, position in estuary) and contaminants. Differences in faunas between the urban and non-urban estuaries were not, however, clear-cut and nor were relationships between faunal assemblages and environmental variables (including contaminants) consistent between two times of sampling.