Sediment toxicity and the distribution of amphipods in Commencement bay,Washington, USA

The toxicity of 175 sediment samples from Commencement Bay, Washington, was measured by the survival of marine infaunal amphipods (Rhepoxynius abronius) during ten-day exposure to test sediment. Survival was high in sediment from offshore, deeper parts of the Bay, including two designated dredge material disposal sites. Within each of the major industrialized waterways there was a wide range in amphipod survival. Both acutely toxic and relatively nontoxic samples were collected from various areas within the Hylebos, Blair, Sitcum and City Waterways. Habitat differences, sedimentation rates, proximity to contaminant sources and sinks, and disruption of the seabed by prop scour and dredging could contribute to this variation in toxicity. Community structure data show a correlation between amphipod distribution and sediment toxicity, with lower amphipod density and species richness in the waterways than in the deeper part of the Bay. Phoxocephalid amphipods, a family that includes the bioassay species, were ubiquitous in the deeper Bay, but absent from the waterways. This correlation between laboratory and field results indicates the ecological relevance of the sediment bioassay.