Fortnight field experiments at the stationary observation point in the Suonada sound，the Seto Inland Sea were carried out at the late summer, when diurnal inequality of tides is rather small like the early spring, to reveal the physical process of the environment near the basin floor. It has been recognized from the experiments that tidal currents were dominant and tidal re-suspension was induced around the spring tide and that temporary currents except tidal currents were generated and re-suspension due to such currents was not observed around the neap tide even when they were rather strong. While tidal re-suspension around the spring tide was induced quarter-diurnally relating to the tidal current speed, the semi-diurnal variation was also recognized which came in view clearly at the flood flow. To investigate such a re-suspension process more minutely, 25 hour field-experiment was carried out using a highly accurate current meter by which the current and turbidity can be measured in 16 Hz. It has been clarified that the power spectrum was larger by one and half times at the flood flow than at the ebb flow and further that the vertical turbulent flux of SS was also larger at the flood flow than at the ebb one.

One of the goals of aquatic ecology and biological oceanography is to determine the qualitative and quantitative aspects of material or energy flow operating in food chains starting from phytoplankton up to higher trophic-level animals，including commercially harvested fish. Due to rapidly growing human activities, it becomes crucial to investigate anthropogenic pressures on the marine ecosystem, in order to sustain fish production. This article summarizes the author's studies on the production ecology of zooplankton, mainly copepods as food for fish, and the recent problematic blooms of jellyfish in both the lnland Sea of Japan and East Asian marginal seas.

Zooplankton, of which copepods are the dominant taxa, play a pivotal role as grazers of primary producers, carbon drivers as secondary producers and prey for economically important fish. For some 30 years, I have been conducting ecological studies of copepods by integrating laboratory experiments (e.g., measurement of respiration, feeding, excretion, egestion, somatic growth, egg production rates) and field surveys (e.g. determination of their taxonomic composition, numerical abundance, stage composition, biomass). Laboratory experiments revealed that the average growth rate of copepods (g, d^-1) increases with increasing temperature (T, °C ), as expressed by g=0.078e^o.062T; it varies roughly from ca. 0.1 d^-1 in winter to ca. 0.4 d^-1 in summer in temperate coastal waters. ln situ surveys in the Inland Sea of Japan, whose fish catch per unit area is among the world's highest (i.e., 20.5 tons WW km^-2 yr^-1 in 1986), revealed that this semi-enclosed sea nurtures the plankton community with an efficient food chain (transfer efficiency: 28% from primary to secondary production, and 25% from secondary to tertiary production). Copepods contribute 74 and 79% of biomass and production rates among secondary producers, respectively, indicating that the phytoplankton-copepod-fish linkage is the main food chain leading to the efficient fish production.

In the last two decades, however, the highly productive fishery grounds of the Inland Sea of Japan have been seriously degraded, as manifested by ar emarkable decline of fish catch and a concomitant increase of jellyfish populations (primarily the moon jellyfish Aurelia aurita s.l.). Our field survey demonstrated that jellyfish carbon biomass usually surpasses prey zooplankton biomass and their predation impact is almost equivalent to the amount of carbon produced by copepods alone. Increased human impacts, such as overfishing, warming, eutriphication, changing nutrient composition, marine construction, etc. may benefit jellyfish more than fish. Since fish and jellyfish are advertisaries competing fot hte same prey resource (e.g., copepods) and can also be prey for each other, itis theoretically possible that if the more jellyfish prevail, the more fish are eradicated. The above-mentioned human-induced perturbations occurring in Chinese coastal waters may be responsible for the recent dramatic proliferation of the giant jellyfish Nemopilema nomurai in the East Asian marginal seas. Thus, the jellyfish-dominated coastal seas constitute an endpoint of marine ecosystem deterioration brought about by recjless human pressures on the environment. Human beings will demand more food from the ocean to feed the growing world population, and hence fishries sustainability in the East Asian marginal seas, the world7s most productive fishery ground, is critically important. lastly, I would like to propose the concept of "sato-umi", a costal sea with high roductivity and biodiversity anchored on rational and beneficial human interaction, where copepod production would be most efficiently transformed into human food.

Surface to intermediate water circulation is related to the climate and biological production through heat/material transports and exchanges. The author has been studying ocean circulation and heat/material transports and exchanges, targeting temperature inversion (temperature increments with depth) and mesoscale eddies in the subarctic North Pacific. Temperature inversions are studied through analyses of climatological and individual oceanic data, and are indicated to be maintained by warm and saline intermediate water transport from the area east of Japan to the northern Gulf of Alaska. Mesoscale eddies in the Alaskan Stream are studied through satellite and profiling float data analyses, and are revealed to have a significant impact on temperature/salinity fields and biological production in the western and central subarctic North Pacfic.

Multi-Channel Seismic (MCS) survey is now a traditional method in seismology to study subsurface structures. Since Holbrook et al. (2003) reported that an MCS section in the Atlantic Ocean can capture a front between cold and warm water masses, the new ap proach in physical oceanography using MCS data, “Seismic Oceanography", has been developed. The MCS data consist of records of sound reflectors in the ocean interior. Although the MCS data are contaminated by relatively greater noise than traditional ocean finescale measurements, the MCS enables a high resolution section (6.25-12.5 m in horizontal, 0.75-3 m in vertical) of the ocean density structures, which is difficult to obtain by traditional methods. It is possible to conduct an MCS profiling without stopping the vessel and it takes only about a day to cover a 200 km long section. We exemplify the utility of MCS data in physical oceanography using an image of a cyclonic eddy in the Izu-Ogasawara region.