A semi-isolated brackish water sulphuretum was studied by analysing the small scale vertical distribution of benthic metazoans in relation to oxygen, sulphide and pH microprofiles and their diurnal variations. Furthermore the resistance of the harpacticoid copepod Cletocamptus confluens to anoxia and sulphide was tested at different pH values by laboratory exposure experiments. Steep oxygen and sulphide gradients were found in the top millimetre of the mud. Experimental stagnation was accompanied by a subsurface oxygen maximum. Continuous measurements showed strong diurnal variations in the chemical environment of the mud-water interface. Apart from protozoans (not dealt with here), only two benthic species were fairly frequent, accounting between them for 89 % of all metazoans found: the harpacticoid C. confluens and the nematode Daptonema setosum (Bütschli 1874). On average 36 % of all C. confluens were found below the chemocline. Sulphide appeared to have no lethal effect in exposure experiments at pH 6.5 and 9.5 under the conditions tested. Field and laboratory investigations suggest that C. confluens possesses a high tolerance for short term exposure to sulphide and anoxia. Quiescence during sulphide exposure may be important for this species, enabling it to populate unstable niches characterised by prolonged periods of anoxia and high sulphide concentrations, freezing and changes in water level, including even up to sporadic air exposure.