ON THE EXCRETION OF ZINC BY THE SHORE CRAB CARCINUS-MAENAS (L)

The shore crab Carcinus maenas (L.) does not excrete zinc taken up and accumulated when exposed to 100 mu g Zn l(-1), but does excrete a pro portion (c. 70%) of the zinc taken up from 3162 mu g Zn l(-1) over 21 days. Of the zinc excreted at this exposure, only 4% is excreted in th e urine. There was a linear relationship between zinc concentrations i n urine and blood. Food was found to be an important Zn source to the crab, and excretion of Zn accumulated from food again depended on dose . None of a c. 25 mu g Zn dose in food was excreted in 12 days; of 210 mu g absorbed from a 250 mu g Zn dose in a meal 46% was retained afte r 12 days, and 113 mu g was excreted (22% in the faeces, 1% in the uri ne and 77% probably via the gills). C. maenas lost c. 20% of the body zinc content with the moult, even after withdrawal into the soft tissu es of some of the zinc there accumulated (both from food and water).