Energy reserves and metal-storage granules in the hepatopancreas of Oniscus asellus and Porcellio scaber (Isopoda) from a metal gradient at Avonmouth, UK.

Isopods taken from populations of Onsicus asellus and Porcellio scaber from long-term polluted sites in the vicinity of metal smelting works at Avonmouth, South West England, and from a control site near Tübingen, South Germany, were examined for the frequency and size of metal-containing granules (spherites), lipid droplets and glycogen in their hepatopancreas. The number and size of spherites in the hepatopancreas of O. asellus increased with decreasing distance to the smelter, but such a trend was not found in P. scaber. A trend towards massive reduction in hepatopancreatic energy reserves (lipid, glycogen) with increasing soil metal pollution was observed for O. asellus while, in contrast, the lipid and glycogen content of P. scaber midgut gland cells was independent of the distance to the smelter. In view of previous reports on metal accumulation and biochemical responses to metal pollution, we propose that the two investigated isopod species, which form stable populations in the Avonmouth metal gradient, use different strategies to survive.