Oxygen and inorganic nitrogen contents and fluxes in burrows of the shrimps Callianassa japonica and Upogebia major

Concentrations of dissolved oxygen and inorganic nitrogenous compounds in burrows occupied by the shrimps Callianassa japonica (de Haan) and Upogebia major (de Haan) were compared to those in the overlying waters under simulated in situ conditions. Dissolved oxygen content in the burrow was considerably lower; it ranged from 12 to 45 % of saturation values for C. japonica burrows and from 30 to 41 % for U. major burrows respectively. One order of magnitude higher values for ammonium and 2 to 3 times higher nitrate plus nitrite values, compared to overlying waters, were also observed. Both oxygen and inorganic nitrogen data indicate that the burrow water is distinctively different from overlying waters and forms a unique microenvironment for benthic microorganisms. Estimated rates of irrigation by the burrowing shrimps, based on the oxygen balance in the burrow at 20.5 "C, were 32 to 89 m1 h-' for C, japonica and 14 and 33 m1 h -' for U. major. Our data suggest that the burrow, formed and maintained by the burrowing shrimps, has roughly the same oxygen consumption and ammonium production as the surrounding sediment surface, the metabolically most active site in the sediment.