The volume of the catch in Japanese sardine has varied over a 60–68 year cycle. In this cycle, a high catch occurs one or two decades and a low catch continues for the rest of the period. This cycle was observed irrespective of any oceanographic conditions around Japan. Parallel cycles on sardine catches have been reported in various regions in the world, and that the period of the cycles and the direction of the changes are similar in distant regions all over the world. This paper examined the relationship between the speed of the Earth’s rotation and the sardine catch volume. The results of this paper include : (i) The cyclical changes in the catch volume of sardine and the Earth’s rotation rate have similar time-scale of about 60 years; (ii) The coefficient of determination between sardine catch volume and the Earth’s rotation rate showed high values, total period for 63 years about R²=0.38 (first period), R²=0.71 (second period) and, R²=0.80 (third period), R²=0.41 (total period), and (iii) Relationship between the fluctuations of the Earth rotation rate and the changes of the primary production volume in the ocean surface was consistent. It was also suggested that original factor behind these phenomena can be explained by the movement of the Earth‘s liquid outer core.

It has been pointed out that the decrease in nutrient concentration is a key factor in the decrease in sand lance catch in the Seto Inland Sea. In this study, aiming at having quantitative insight into the productive structure of sand lance, elucidating the relation with the nutrient environment, a Lagrangian numerical model of sand lance coupled with Eulerian lower-trophic ecosystem model was developed to simulate annual life cycle of the fishery resource. The model was validated with numerical experiment over the 3-year period from 2016 to 2018. As a result, the growth dynamics of sand lance from hatching through aestivation to spawning and hatching, as well as ecological features of the lower trophic ecosystem including plankton abundance and nutrient stocks, were reproduced fairly showing a good agreement with the observational data. The model turned out to provide a quantitative evaluation on the interaction between sand lance—the higher trophic organism— and plankton and nutrients—the lower trophic constituents—. Regarding the aestivation of sand lance, about 80% of all aestivating individuals settled down on the sandy seafloor in the eastern part of the Harima-Nada, such as Shikanose and Murotsunose, showing that the aestivation grounds were well reproduced. In terms of carbon flux, the transfer efficiency from primary production to secondary production during the peak of the 2016 fishing season around the Akashi Strait, the main fishing ground of sand lance, was as high as 45%. This indicates that zooplankton (copepods) exerted intensive feeding pressure on phytoplankton (diatoms) and led to the chronical shortage in abundance during this period.

Productivity decline has become a problem in seaweed aquaculture in Izonoura. Analysis based on field observations has pointed out the possibility of a decrease in nutrient elution from sediment in addition to river load. However, the amount of nutrients eluted from the sediment is complicatedly related to the biological and chemical cycle structure, the individual metabolic process of the organism, and the physical and chemical properties. Therefore, indirect estimation based on some observations is not accurate enough.

In this study, in order to quantitatively grasp the balance of nutrients, we used an ecosystem model, that couples the pelagic and the benthic ecosystem is incorporated into the flow model that reappearance the physical environment.

Using an ecosystem model that reappearance the current nutrient environment, predicted the nutrient environment at that time using the river load and the abundance of benthic organisms at the time when the production of Monostroma nitidum was relatively high.

As a result, the concentration of nutrients in the water column in the past was more than double the current concentration. In the past, nutrients were directly supplied by higher river loads than at present, and indirectly, there was a large amount of elution from sediment due to the abundance of benthos supported by high primary production. It was considered to be the reason why the nutrient concentration in the water column was high in the past.

Recently, a great interest has been observed in using marine species for coastal environmental impact assessment. Embryos of brown macroalga, Sargassum horneri, distributed throughout the northwest Pacific coast, appear be a promising marine indicator for such assessments. This study identified the effects of copper (Cu–EDTA) on the germling growth of S. horneri. Following exposure to various copper concentrations for 21 days, the germination rate, specific growth rate, and final thallus area of S. horneri germlings were measured. The germination of the embryo was completely inhibited when exposed to 10 µg/L, and the no observed effect concentration (NOEC) for germination was estimated as 5 µg/L. Since the incubation period was longer for lower copper concentrations, growth inhibition could be clearly observed and was deduced to be a chronic toxicity effect. The median effective concentration (EC₅₀) and NOEC for the final thallus area were 0.50 and 0.16 µg/L, respectively. The results demonstrated that the embryos of S. horneri are more sensitive to copper than other seaweeds, further suggesting that its growth patterns can effectively be utilized to assess coastal environmental impacts.

We examined the microplastic encapsulation capacity of a freshwater cladoceran zooplankton Daphnia magna, which is a typical species in the freshwater ecosystem. To read the possible relevance of encapsulation capacity to the food in the medium, and to understand under which condition the encapsulation capacity is higher, experiments were performed with 12 individuals of D. magna in each medium on 6 (3 of them contain ϕ=10 µm polystyrene microspheres) different media. After the experiment, the gut volume was measured with a digital microscope. Subsequently, the approximate number of particles in the gut was determined using the Kepler conjecture. The surface area of the plastic particles encapsulated was calculated in the diet range, suggesting that the total surface area of plastic particles in a Daphnia magna gut may reach around as much as that of two soccer balls.

Investigations of air–water momentum and heat transport at extremely high wind speeds are crucial. Three different types of wind wave tanks are used to develop a method for investigating transport in laboratories using a tank with removable solid or net bottom walls to suppress wind wave development. The wind profile and water–level fluctuations are measured by Pitot tubes, differential manometers, and wave gauges. The air-side friction velocities are estimated using the profile method. The friction velocities are damped in the cases with the removable solid or net bottom walls, because the wind wave suppression due to the bottom wall provides a small form drag that acts on the wind waves. Through the rearrangement of the previous wind and wave values measured in a Russian tank, the usefulness of the presented wind wave suppression method is demonstrated for future investigations of the air–water momentum and heat transport at extremely high wind speeds. Moreover, the method can be applied to clarify the effects of the fetch on the air–water momentum and heat transfer at extremely high wind speeds.

Drag coefficient on the ocean surface is determined by various studies based on different mechanisms, such as turbulence and wave breaking, closely related to wind speed. The global ocean datasets of wind speed are distributed by various temporal resolutions based on reanalysis, assimilation, and satellite data. Recently, the wind speed data with higher temporal resolution have been provided. Using 6-hourly and hourly wind datasets, the air-sea momentum fluxes were estimated by several drag coefficient models proposed by Large & Yeager (2009), Andreas et al. (2012), Takagaki et al. (2012), & Hwang (2018). The globally averaged annual mean air-sea momentum fluxes were derived from the different drag coefficient models. The maximum difference of the annual mean values among the models reaches approximately 30% of annual mean values. The meridional structure of zonally averaged annual mean air-sea momentum flux has double peak at relatively higher latitudes from 40°S/N to 60°N/S. At those peaks maximum difference among the models reaches more than 30% of the zonally averaged annual mean. In terms of differences in temporal resolution on the wind speed datasets on each grid, the differences between hourly and 6-hourly wind data became larger with decreasing average period. The maximum difference of 66.7% was recognized on daily mean. The large difference was remarkable in higher wind speed regions, such as typhoon’s paths in the western Pacific. The effects of wind variability on different temporal resolution datasets are significant for estimating the air-sea momentum flux.

Obatake-Seto, located in Inlandsea of Japan, is famous for its strong tidal currents, the maximum speed of which is about ±6–7 kn (positive indicates an eastward flow, and negative, westward). The Komatsu-Ko port area is located at the northwest side of Suo-Oshima Island. The currents around this area, which have a speed of about 0.5–1.5 kn, are caused by the currents of Obatake-Seto, and the speed and direction of these currents have complex characteristics due to the area’s terrain. To clarify these characteristics, we investigated the current speed and direction, over a period of approximately one month, at three stations in the Komatsu-Ko port area. Measurements were made using an Acoustic Doppler Current Profiler “ADCP” or electromagnetic current meters at each station. From these observations, phase differences between the main currents and local currents, at the spring and neap tide periods, as well as the presence of counter currents were identified.