METAL LEVELS IN 7 SPECIES OF MOLLUSK AND IN SEAWEEDS FROM THE SHANNONESTUARY

Metal levels (iron, zinc, manganese, cobalt, chromium, copper and nick el) were determined ill Cerastoderma edule, Mytilus edulis, Monodonta lineata, Patella vulgata, Nucelia lapillus, Littorina obtusata and L. littorea at two sires close to the mouth of the Shannon Estuary (Irela nd) in November 1993 and May 1994, using standard atomic absorption sp ectrophotometer techniques. Samples of seaweeds were included at one s hore for comparative purposes only. The best all-round indicators for all the metals studied were C. edule, M. edulis and N. lapillus. Metal levels ill the seaweeds were much lower than in the molluscs. No spec ies was a universal indicator of the metals studied when site and seas on were taken into consideration. High levels of metals accumulated fr om water and/or sediment were observed in a number of cases. Levels of Zn in N. lapillus were significantly different to those in all other species and C. edule had high levels of Ni. These levels were dependen t on site and season. A detrended correspondence ordination showed tha t the two species of bivalve mollusc and P. vulgata formed one cluster and that the remaining gastropod species formed a second cluster. Thi s study shows that species-specific bioaccumulation occurs and is seas onally specific in certain species. This needs to be taken into accoun t when choosing a bioaccumulator model and when comparing data from di fferent studies.