SULFIDE METABOLISM IN THALASSINIDEAN CRUSTACEA

Sulphide occurs widely in marine sediments and is highly toxic to most organisms. Its principal poisoning effect occurs at extremely low con centrations and is the result of inhibition of mitochondrial cytochrom e c oxidase. Mud-shrimps (Crustacea: Thalassinidea), construct burrows in sublittoral muddy sediments. The sediment in which they burrow is markedly reduced and conditions within the burrow are usually hypoxic and hypercapnic. Field measurements indicate that the shrimps may be e xposed to potentially toxic levels of sulphide in the burrow water (ra nge 0-206 mu M, N=37). Laboratory experiments carried out on Calocaris macandreae, Callianassa subterranea and Jaxea nocturna have shown tha t these species have a high tolerance of sulphide. An oxygen dependent detoxification mechanism exists to defend cytochrome c oxidase from s ulphide poisoning. The main detoxification product of this mechanism i s thiosulphate which accumulates rapidly even during brief exposures t o low concentrations of sulphide. Sulphite also appears as a secondary detoxification product. Aerobic metabolism can be maintained even und er severe hypoxia and toxic sulphide conditions. The mud-shrimps switc h to anaerobiosis when the detoxification mechanism is saturated. Thes e data indicate that mud-shrimps are physiologically adapted to tolera te elevated levels of sulphide that they may encounter in their natura l habitat.