Sediment-mixed biofilms of microorganisms embedded within an extracellular polymeric substance were reconstructed using laboratory models of seawater-benthic boundaries, and the sulfide dynamics in the boundary zone were examined. Biofilm-covered sediment was obtained from the field and cultured in a beaker of seawater with a granular formula for fish larvae and powdered foraminiferal limestone. In the standing culture, a floating biofilm formed on the liquid surface, and a microbiota capable of mixed biofilm formation was obtained. The mixed biofilm was cultured in a fluidization-free aerobic state, again with nutritional granules and powdered
foraminiferal limestone. This culture formed a sediment-mixed biofilm on the bottom of the beaker. Furthermore, a seawater-benthic boundary model was developed on a hydrated substratum with sediment biofilm, using a nylon mesh as the model bottom layer in the culture system. When the floating biofilm was disrupted and then dispersed on the nylon mesh, detectable biofilms formed on the surface of the model bottom. As nutrients were utilized by the microbes, sulfides accumulated beneath the model bottom. Subsequently, the sulfides passed through the model bottom and became detectable in the seawater just above the sediment-mixed biofilm, where a white-turbid layer formed. As revealed by denaturing gradient gel electrophoresis, the layer contained populations of several bacterial species.
We newly developed a fishing gear Vertical Longline for Sharks（VLS）to effectively study the depth distribution of sharks, and compared its efficiency with that of horizontal longlines. This gear consists of a main line（245 m), branch line（5 m each), and galvanized iron hooks（13 pcs). Trial operations with VLS were conducted monthly in Sagami Bay from July 2014 to February 2016 using RT/V Seiyo Maru（170 t）of Tokyo University of Marine Science and Technology. The problems of VLS were twisting of the main line and the branch lines, which often caused tangling to each other. Making major adjustment 5 times through 20 trial operations, we reduced the rate of the branch lines’ tangling by 16% and improved the working efficiency of VLS. Based on the results, we discussed the causes of（1）the main line’s twisting and （2）the branch lines’ tangling. Catch per unit effort （CPUE: number of sharks captured per 1,000 hooks） of VLS was 9.7, showing the fishing efficiency was comparable to horizontal longlines conventionally operated in Sagami Bay. To be noted is that Shortfin mako shark was captured for the first time during the operation in January 2015, and eventually 6 sharks in total by February 2016.