Heavy metal contamination of the Severn Estuary and Bristol Channel : detecting environmental impact using the shrimp Crangon crangon
The Severn Estuary and Bristol Channel have a long history- of metal contamination from anthropogenic sources. Nonetheless, the Estuary- supports a large and varied faunal community including a large population of the brown shrimp Crangon crangon, which is a key species in the ecosystem. The aim of this study was to detect the impacts of chronic metal contamination in the Severn Estuary by studying the effects of metal on shrimp at the individual and population level. Shrimp were collected from the Severn Estuary and Bristol Channel and, for comparison, from the Greater Thames Estuary and analysed for metals. Metals were highest in shrimp from the Severn Estuary where cadmium was very- bioavailable. Cadmium concentrations were up to 30 times higher in Severn shrimp (15 ug g-1) than in Thames shrimp (0.5 ug g-1 although the two sites had similar environmental conditions. Chronic environmental metal exposure of Severn Estuary shrimp may have produced a cadmium tolerant population. Severn shrimp had a significantly higher LC50 and LT50 than reference shrimp from an uncontaminated site and greater levels of metallothionein were induced by cadmium exposure. Metallothionein may act as a mechanism of tolerance by sequestering harmful metal ions. Prey consumption and burying success was reduced in crangon after
exposure to environmentally realistic concentrations of cadmium that were 1O fold lower than the 96 h LC50' Impairment of these behaviours may alter fitness and have consequences for population increase. However, Severn Estuary shrimp were more
successful than the reference shrimp indicating a greater tolerance of the sub-lethal effects of cadmium exposure.
This study has shown that Severn Estuary shrimp are able to accumulate exceptionally high levels of cadmium and show increased tolerance to acute and sub-lethal effects of cadmium exposure. These adaptations exemplify the environmental impact of heavy metal contamination in the Severn Estuary.