VERTICAL-DISTRIBUTION OF CLETOCAMPTUS CONFLUENS (COPEPODA, HARPACTICOIDA) IN RELATION TO OXYGEN AND SULFIDE MICROPROFILES OF A BRACKISH-WATER SULPHURETUM

A semi-isolated brackish water sulphuretum was studied by analysing th e small-scale vertical distribution of benthic metazoans in relation t o oxygen, sulphide and pH microprofiles and their diurnal variations. Furthermore, the resistance of the harpacticoid copepod Cletocamptus c onfluens (Schmeil 1894) to anoxia and sulphide was tested at different pH values by laboratory exposure experiments. Steep oxygen and sulphi de 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 environ ment of the mud-water interface. Apart from protozoans (not dealt with here), only 2 benthic species were fairly frequent, accounting betwee n them for 89% of all metazoans found: the harpacticoid C, confluens a nd the nematode Daptonema setosum (Butschli 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 th at C. confluens possesses a high tolerance for short-term exposure to sulphide and anoxia. Quiescence during sulphide exposure may be import ant for this species, enabling it to populate unstable niches characte rised by prolonged periods of anoxia and high sulphide concentrations.