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

Abstract

アナジャコ類の生息する巣穴の溶存酸素濃度と無機窒素化合物濃度を、野外実験を模擬した水域の溶存酸素濃度と比較した。巣穴内の溶存酸素濃度はかなり低く，C. japonica 巣穴では飽和値の12～45％，U. major 巣穴では30～41％であった。また、アンモニウムの値が一桁以上高く、硝酸塩と亜硝酸塩の値も周辺海域に比べて2～3倍高くなっていた。酸素と無機窒素の両方のデータから、この巣水は周辺海域とは明らかに異なり、底生微生物にとって独特の微小環境を形成していることが示唆された。20.5℃での酸素バランスに基づいて推定した灌漑量は，C, japonicaで32～89 m1 h-'，U. majorで14～33 m1 h-'であった。これらのデータは，アナジャコ類が巣穴を形成し，維持していることを示唆しており，堆積物の中で最も代謝が活発な場所である周囲の堆積物表面とほぼ同じ酸素消費量とアンモニウム産生量を有していることを示唆している。 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.