ECOLOGY OF GASSY, ORGANIC-RICH SEDIMENT IN A SHALLOW SUBTIDAL AREA ONTHE KATTEGAT COAST OF DENMARK

Mats of algae are frequently washed inshore along the sandy beaches in the Kattegat after storms and subsequently buried by sand deposition. Sediment cores were taken in May 1991 from one such shallow subtidal area, from which gas bubbles were being released. The organic-rich lay er was less than 4 cm thick; it had extremely high sulphate reduction rates, up to 1.7 mmol sulphate reduced dm -3 d-1; high hydrogen. Up to 100 mumol dm-3; methane, up to 54 mumol dm-3; and hydrogen sulphide i n excess of 1 mM. No macrofauna were found in this quicksand area and most of the meiofauna were confined to the uppermost 2 cm. The only me tazoan to occur below the 6 cm zone, and down to a depth of at least 3 4 cm, was the nematode Sabatieria longispinosa. The anaerobic ciliate Trimyema sp. cf. marinum and the anaerobic flagellate Hexamita sp. dom inated the highly reducing, organic -rich zone at 2 to 6 cm depth; the y also occurred below this zone together with a few specimens of Euplo tes sp.