It seems that physical processes in coastal regions have been investigated from the macroscopic perspective. Although the boundary between land and sea is spread over an area called a“tidal flat”, physical processes such as tidal flow in this area have hardly been investigated. As scientific and quantitative knowledge has not been accumulated, the value of tidal flats in coasta areas has been neglected, resulting in easy land reclamation and the destruction of coastal environments. In this article, physical processes in mangrove areas, which consist of vegetation on tidal flats, are introduced. By providing basic knowledge on this issue, more advanced investigations of tidal flats are expected to progress.

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My 58-year history of coastal oceanography from the definition of tide-induced residual current to the Satoumi concept is reviewed.

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Flow and material transport in enclosed coastal seas, which have been revealed during recent decades, are briefly reviewed. Density-driven current, tidal current and wind-driven current were shown to be the major flows that transport materials in enclosed coastal seas in Japan.

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The coastal seas and river watersheds of Sendai Bay are now facing a serious environmental problem, namely, radioactive pollution. The radioactive pollutants that fall on the land and sea surfaces in the region are transported by snow-melt and rainwater through the rivers to the coastal seas. Floating pollutants circulate there. In order to combat this problem, advanced new technology for monitoring the earth’s surface plays a dominant role. Milestone-1 :“A high-resolution visible and infrared radiometer will be a fundamental tool for monitoring the surface conditions of coastal zones, especially for understanding physicalchemical- biological interactions at the sea surface that control the dynamic state of radioactive pollutants.” Since systems for observing the atmosphere and ocean have improved over the last two decades, our ability to analyze the present status of bulk air and seawater around Mutsu Bay and to predict their future conditions has improved drastically. However, there are many unknowns, that is, challenging scientific subjects, related to the sea surface, which covers 70％ of the earth’s surface. Milestone-2 :“Shifting our study areas from bulk seawater, through the skin layer, to the sea surface.”

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Research activities of the author in coastal oceanography are summarized by describing achievements in graduate school, the Hydrographic Department of the Japan Coast Guard, and the Atmosphere and Ocean Research Institute of the University of Tokyo, including their research environments. Oceanographic research and observations in the coastal waters promoted by the Intergovernmental Oceanographic Commission of UNESCO, for which the author has been acting as one of the vice chairs since 2011, are also described mainly over the last20years, including the concept of Marine Spatial Planning.

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In the first paradigm of the physical oceanography in coastal waters, oceanographers have just collected information on currents and hydrographic properties in specific oceans as naturalists. In the second paradigm, they have explored the physical oceanography in coastal waters as a superposition of physically elemental processes such as tidal and wind-driven currents. Emphasized in the present study is the third paradigm, where oceanographers recognize coastal waters as a combination of physically elemental regions such as ROFI and stratified oceans.

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Owing to the high flexibility of tidal estuaries and the unknown extent of the coupling between the chemical and the biological processes there, there is a need for a conspicuous set of data enabling description of the dynamics of bio-elements（e. g., C, N, P and Si）. As such, a long-term and multidisciplinary approach is appropriate. The chemical characters of water and sediments were examined from May 1993 to March 2002, monthly, in both an intertidal flat and a subtidal zone. Laboratory experiments were performed on the nutrient excretion rate of the dominant macrozoobenthos species. These works were carried out in the context of a long-term project planned to quantify the dynamics of bio-elements, to evaluate the roles played by the macrozoobenthos on the above processes and to propose a final budget on the dynamics of bio-elements for the sustainable use of tidal estuaries.

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The author reviews research progress on marine phosphorus, the most essential bioelement after carbon and nitrogen, in particular in terms of inositol hexakisphosphate（IP6）, in sediments, which is one of the few organic phosphorus compounds identified in marine environments. In terrestrial soils, IP6and its related compounds have been analyzed and identified to be the most abundant forms of soil organic phosphorus. Application of the protocols for soil IP6 analysis to marine sediment samples, however, was extremely difficult, but finally quite low concentrations of IP6were determined in Tokyo Bay sediments. This is one small step for the identification of organic phosphorus in marine sediments, but one giant leap for understanding phosphorus cycling between land and coastal marine environments.

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I have been studying coastal oceanography in the Seto Inland Sea for20years since obtaining my present post of professor at Kagawa University. During my undergraduate student days at the Department of Agrochemical Science, I experienced an array of chemical experiments in laboratory classes. Since majoring in oceanography, I have often worked onboard ships where I conducted hydrographic observations. Indeed, I learned from contact with people who work in many different study fields that oceanography is an integrated science of various academic disciplines. I feel that it is very important to integrate study methods of different research specialties and to carry out cooperative research with people specializing in different coastal oceanographic study disciplines. Moreover, upon continuing coastal oceanographic research over a long period, researchers have to appreciate the importance of their own study, as well as making a social contribution by their research achievements. Kagawa University is located in a rural area and does not have a faculty and department of oceanography. Although open ocean study optimally involves a large project team and research vessels, coastal oceanography is still available for academics who are strongly interested in it. I would like younger generations to study oceanography by combining at-sea studies among a wide network of human interactions. I hope this paper will be a milestone for young researchers and students to seek success in coastal oceanography.

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Traditional definitions of biological diversity and their measurement are briefly reviewed, focusing on their utility and confusion related to spatial scale. Then, utilizing data on exotic as well as endangered aquatic invertebrates in Ise Bay and its neighboring areas along the Pacific coast of Central Japan, the crisis in biological diversity in Japanese coastal waters（i.e., increasing exotic species together with endangered species）is discussed in relation to the loss of habitats of the endangered species, but the provision of new habitats for exotic species, owing to rapid coastal development.

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Seaweed and seagrass form beds in shallow coastal waters. They are called moba in Japanese. The authors studied how these beds influenced the local physio-chemical environments. The studies revealed that moba exerted distinctive influences on the water flow, light, water temperature, water density, dissolved oxygen and pH within the beds. In this way, moba forms unique environments and provide important habitats for organisms in coastal ecosystems. It is indispensable to determine its spatial distributions using efficient and precise methods for the conservation of moba. Thus, we developed remote sensing methods for the mapping of moba using ultrasound and light, not conventional diving observation. In moba, leaves and fronds are detached from the substratum or basal parts by wave action once plants reach a large size. Most of the plants are transported to offshore waters as floating rafts due to buoyancy. The ecology, distribution, transport and origins of floating rafts in Suruga Bay and the East China Sea from coastal moba were studied. Seaweed and seagrass are very important not only in coastal waters through forming moba, but also in offshore waters through forming floating rafts. Namely, they produce a dynamic ecosystem changing from a sedentary stage to a floating stage in the sea

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The budgets of dissolved oxygen in Dokai Bay in 1994, when hypoxia developed, and in 2011, when hypoxia disappeared, are compared, and the mechanism of hypoxia disappearance is clarified.

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Characteristics of seawater quality in Ise Bay from1989 to 2006 were studied using the data of chemical oxygen demand （COD）, total nitrogen（T－N）, total phosphorus（T－P）, dissolved oxygen（DO）and chlorophyll a（Chl. a）at the upper and bottom layers obtained by a wide-area comprehensive water quality investigation in Ise Bay that was announced officially by the Ministry of the Environment. At the upper layer, averages of COD, T－N, T－P, DO and Chl. a from 1989 to 2006 were 2．5mg L－1, 0．41mg L－1, 0．037mg L－1, 8．6mg L－1 and 9．1μg L－1, respectively. The trend of annual average of COD was a leveling off or slight increase. The trends of others involved leveling off. At the bottom layer, averages of COD, T－N and T－P from 1989 to 2006 were 1．6mg L－1, 0．33mg L－1 and 0．036mg L－1, respectively. Their trends of annual averages involved leveling off. At the bottom layer, averages of DO and Chl. a from1989to2006were6．4mg L－1 and3．4μg L－1, respectively. Their trends of annual averages involved leveling off. In terms of seasonal changes, according to the results of rincipal Component Analysis, at the upper layer, it was suggested that the degree of organic and nutrient pollution increased in the order of winter→spring→summer, and decreased in the order of summer→fall→winter. Furthermore, at the upper layer, it was suggested that DO decreased in the order of spring→summer→fall, and increased in the order of fall→winter. At the bottom layer, it was suggested that DO decreased and T－P increased from spring to summer. While DO increased, T－P conversely decreased in the order of summer→fall→winter, and organic pollution levels of COD and Chl. a were almost constant throughout the year.

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