ABSTRACT

Submarine hydrothermal activity can hardly be detected by measuring water temperature or found by conventional methods like ³He, CH₄ and/or metal ions measurements except through time consuming procedures. We applied a rapid and ultra-sensitive colorimetric method to measure the concentration of lipopolysaccharide (LPS), an indicator of bacterial biomass, in seawater around the Izu-Ogasawara Arc, northwestern Pacific, where the presence of hydrothermal activity is suggested. High anomalies of LPS at ca. 50 m-water layer above the sea bottom were discovered in a submarine caldera along the volcanic front and in a back-arc depression. Many extraordinarily large-sized bacteria were also discovered in the sample containing high LPS concentration. It takes only about an hour to analyze LPS after obtaining a sample, and a mere 100 μl of seawater sample is enough for this method. This method should be very effective for the purposes of prospecting the hydrothermal activity.