MEPS 187:159-170 (1999)  -  doi:10.3354/meps187159

ABSTRACT: The blackening of tissues or mucus of benthic animals from sulphidic environments is a remarkable phenomenon whose ecological interpretation is disputed. In the Baltic clam Macoma balthica the mantle edge turned black after sulphide exposure owing to numerous precipitates in the extracellular matrix underneath the epidermal cells. In the apical parts of these cells, similar precipitates were found, albeit in lower abundance. Elemental analyses showed that copper (214.7 µg g^-1 ww [wet weight]) and sulphur (1328.6 µg g^-1 ww) were the main components, with iron (311.2 µg g^-1 ww) and zinc (112.7 µg g^-1 ww) in lower concentration. Apparently, these precipitates become phagocytosed by amoebocytes and concentrated in haemocytic granules. This is interpreted as a pathway of removal from the mantle edge. On the basis of calculated diffusion rates (D_HS^- = 1.9 x 10^-6 cm² s^-1), there is a sulphide influx of 61 nmol h^-1 into the body of M. balthica. Even under conservative assumptions, this would lead to the binding of all the copper present in about 30 min. It is concluded that the process of sulphide precipitation can represent a temporarily effective pathway attenuating sulphide toxification.

KEY WORDS: Macoma balthica · Baltic Sea · Bivalves · Hydrogen sulphide · Diffusion · Detoxification · Anoxia · Heavy metals · Ultrastructure · Elemental analysis