SIGNIFICANCE OF BODY-SIZE IN SULFIDE DETOXIFICATION IN THE BALTIC CLAM MACOMA-BALTHICA (BIVALVIA, TELLINIDAE) IN THE GULF-OF-GDANSK

The Baltic clam Macoma balthica, a predominant species of macrofauna i n the Gull of Gdansk (Poland), is exposed to high concentrations of hy drogen sulphide at many locations in this bay. When oxygen is availabl e, the species is able to detoxify penetrating sulphide mainly by oxid izing it to non-toxic thiosulphate. Sulphide influx rate can be quanti fied by calculation of the diffusion coefficient for total sulphide. A relatively low apparent diffusion coefficient of about 2 x 10(-6) cm( 2) s(-1) indicates that M. balthica is able to reduce sulphide diffusi on by temporary valve closure. During oxic-sulphidic incubation, an eq uilibrium between sulphide diffusion and detoxification is established at a specific internal sulphide concentration, c(j), which can be cal culated by the following equation: c(i) = c(0) e(-kr2e/3D) where c(i)= internal sulphide equilibrium concentration, c(0)=external sulphide co ncentration, k=apparent detoxification constant, r(e)=effective radius , and D=apparent diffusion coefficient. The amount of accumulated sulp hide in the tissues is strongly dependent on individual size. This is confirmed by experiments as well as by field studies. After specific s ulphide incubations, only low internal sulphide concentrations are fou nd in large clams, whereas small clams accumulate much more sulphide i n the tissues. Field studies show a distinct reduction in numbers of s mall clams in high sulphidic areas. We conclude that efficient sulphid e detoxification seems possible only ii the body size exceeds a certai n minimal value.