VARIABLE TRANSFER OF DETOXIFIED METALS FROM SNAILS TO HERMIT-CRABS INMARINE FOOD-CHAINS

In any polluted marine environment, different invertebrate species con tain markedly different concentrations of heavy metals. Primary produc ers take metals from seawater, but animals take additional metals from diets of animals, plants and detritus. Metals in a dietary organism o f a food chain have varying reactivities and they follow different bio chemical pathways. Excess metals are bound by ligands to form insolubl e compounds within cytological compartments. These metabolic systems p revent the disruption of normal biochemical reactions by metals. The p resent work on Mediterranean invertebrates, initiated in Greece in 199 3, used digestive glands from three species of marine snail, Monodonta mutabilis (Philippi), Cerithium vulgatum (Bruguiere), and Murex trunc ulus (Linnaeus) as prey tissue, and hermit crabs Clibanarius erythropu s (Latreille) as predators; the digestive glands and faecal pellets fr om all animals were analysed by atomic absorption spectroscopy and x-r ay microanalysis. Most metals detoxified by the snails are unavailable to the crabs and they pass straight through the gut and appear in the faecal pellets. This applies to significant proportions of the mangan ese, nickel, copper, zinc and silver which are bound electrostatically to phosphate or covalently to sulphur within membrane-bound intracell ular compartments. Cadmium and chromium are transferred to the crabs. In digestive glands of snails, cadmium is bound to soluble high-sulphu r protein in the cytosol; the cytology of chromium in these animals is not known.