底層の貧酸素化が内湾浅海底生生物群集の変化に及ぼす影響

Abstract

Changes in the benthic community structure, relating to a decline in bottom dissolved oxygen concentration in the shallow muddy bottom of Mikawa Bay, were observed throughout a 50 days period during the early summer of 1996. Water mass movements related to tides and winds were largely responsible for changes in the bottom oxygen concentration. During the observation period, the dissolved oxygen deficiency tended to progress as the water temperature increased, which probably caused an increase in decomposition of organic matter on the bottom. An increase in the apparent dissolved oxygen consumption rate was mainly due to decomposition of newly deposited organic matter from water column rather than that of existing bottom sediment. Biomass of bacteria increased during the early stage of the dissolved oxygen deficiency, but decreased in the later stage, resulting in an increase of undecomoposed detritus in the sediment. Benthic chlorophyll fluctuated mainly with changes in sunlight intensity, but decreased when severe dissolved oxygen deficiency conditions prevailed. Differeces in the ability to tolerate the oxygen deficiency amongst meio-and macro-benthos species were observed. Almost all benthos species, however, decreased during the severe oxygen deficiency period, except for subsurface deposit feeders.