Spatial variation of trace metals within intertidal beds of native mussels (Mytilus edulis) and non-native Pacific oysters (Crassostrea gigas): implications for the food web?

Abstract Pollution is of increasing concern within coastal regions and the prevalence of invasive species is also rising. Yet the impact of invasive species on the distribution and potential trophic transfer of metals has rarely been examined. Within European intertidal areas, the non-native Pacific oyster (Crassostrea gigas) is becoming established, forming reefs and displacing beds of the native blue mussel (Mytilus edulis). The main hypothesis tested is that the spatial pattern of metal accumulation within intertidal habitats will change should the abundance and distribution of C. gigas continue to increase. A comparative analysis of trace metal content (cadmium, lead, copper and zinc) in both species was carried out at four shores in south-east England. Metal concentrations in bivalve and sediment samples were determined after acid digestion by inductively coupled plasma-optical emission spectrometry. Although results showed variation in the quantities of zinc, copper and lead (mg m-2) in the two bivalve species, differences in shell thickness are also likely to influence the feeding behaviour of predators and intake of metals. The availability and potential for trophic transfer of metals within the coastal food web, should Pacific oysters transform intertidal habitats, is discussed

Factors influencing the bioaccumulation of persistent organic pollutants in food webs of the Scheldt estuary

Concentrations of several persistent organic pollutants (POPs: PCBs, PBDEs, OCPs) in aquatic species from the Scheldt estuary were related with factors (body size, lipids, trophic position), possibly influencing their bioaccumulation. Stable nitrogen isotope ratios (δ15N) were used as a measure for trophic position. A decreasing trend in POP levels towards the sea was observed. For POP concentrations in sediments, this trend could be attributed to a dilution effect from mixing with seawater. However, concentrations in biota more downstream were higher than expected after taking into account the dilution effect, possibly due to differences in bioavailability. Tissue concentrations were correlated with the lipid content in biota, but not with body size. Biomagnification was only significant for some PCB congeners and p,p'-DDE at the most marine sampling location (Terneuzen, L1) and for p,p'-DDD and BDE 100 at the second sampling location (Bath, L2). A significant decreasing relationship was found for ɣ-HCH concentrations with increasing δ15N at Terneuzen. For Antwerpen (L3), no significant relationships were detected. TMFs ranged from 0.64 for ɣ-HCH up to 1.60 for PCB 194. These results suggest that biomagnification was more important in the marine part of the estuary, although the presence of multiple carbon sources at the freshwater side might have led to an underestimation of the influence of trophic position