The coastal zone forms an ecotone between the sea and the land and bears one of the most productive ecosystems on the earth. Environmental conservation of this zone is essential since it has rich biodiversity and provides resources not only to humans but also to the sea and land ecosystems. In Japan, however, the natural environment of the coastal zone has been damaged primarily by human impact. Construction of artificial structures aiming at protecting erosion from disastrous high waves resulted in more than a half of Japanese seacoasts covered by artificial structures in recent forty years. Particularly, the wetland seacoasts are fragile and their ecosystems have been seriously degraded. Coastal fisheries have shown the degradation of biodiversity and the biomass in the seacoast ecosystems. Recently, however, some artificial structures have been built. for natural restoration and creation. Seacoast Law of Japan revised definitions of the terms of environmental factors in 1999. This new social scheme may provide new thought for construction affairs. In this special issue, environmental coastal and fishery engineering, the integrated study of ecology and engineering, the contribution of amateurism, new visions of the revised Seacoast Law, partnership of scientists, engineers, and citizens, long-term monitoring of local naturalists are addressed in order to elucidate the present situations, aims and the future perspective on Japanese seacoast environmental conservation.

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Geomorphological features of the spawning sites of the horseshoe crab Tachypleus tridentatus were investigated in two river mouths in Moriye Bay in Oita Prefecture, one of the well-known habitats of the horseshoe crab in Japan. Its spawning sites were found at the inner sand bar of the river bend near the mouth, at the river mouth bar, and at a sandy beach surrounded by a tidal flat. The elevation and the median diameter of bed materials at the spawning sites were 0.62±0.18m (mean±SD) above the M.S.L. and ranged between 0.4 mm and 1.0mm, respectively. Dispersion patterns of the hatchlings were estimated by a float tracking experiment in the field. The result indicated that the hatchlings, which came out of the sand surface during high tide, could reach the larval habitat at the tidal flat by tidal currents in spite of their poor swimming ability. Mitigation methods necessary for construction of artificial spawning sites are proposed based on these field observations.

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The author examined roles of fishery engineering in conservation of coastal ecosystems. Fishery engineering is a field whereby the marine environment is controlled. It focuses on the physical elements among non-biological factors in order to develop methods for habitat rehabilitation and restoration through environmental control in the coastal environment. In this paper I presented a method for environmental assessment that clarifies relations between marine organisms and their environment. Waves, which are a major physical environmental factor for coastal marine organisms, can be treated as a flow. Regarding the influence of flow on marine organisms, I showed examples of the tests made in oscillating flow tanks and discussed on what should be considered in applying the results. Environmental control by a structure will exert side effects that are not always anticipated before the installation of the structure. Finally, I showed that concrete, a major material of artificial structures, could enhance habitat function as substratum for marine organisms when efforts would be made toward this end.

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Some issues of coastal works in Japan are discussed from the aspects of ecosystem conservation. A vast length of the Japanese coastline has been covered with concrete armor units to prevent beach erosion. Such coastal works were accelerated for many reasons during the rapid economic development era in this country. Installation of these concrete armor units along the shoreline was very effective for dissipation of wave energy, but it ruined the scenic beauty and wild life habitats along the coast. In this paper, the background of this situation in Japan was described in relation to the seacoast law. In order to change the situation and alter the present coastal works, the following is required: develop planning methods under consideration with coastal ecosystem conservation, investigate the monitoring methods, and establish public involvement in coastal zone management

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The eco-social system is dedined as interrelations among the natural environment, society and social activities. Maintaining fishing villages in a good condition requires efforts to keep several eco-social factors and their interrelations within an acceptable range of variations: the fishery, the life and culture of these villages, and the coastal environment including hinterland forests. In fishing villages, one must consider the following in terms of their interrelations : industrial activities and the preservation of specific industries, lifestyle and culture, and the natural environment. Focusing on the fishery or living convenience alone prompts the disintegration of a fishing village's eco-social system. On the other hand, in a discussion on the ecosystem conservation, we should not limit ourselves to specific endangered species and their environments. We should consider preservation in relation to the lifestyle of the village's people and its fishery. This study considers examples of conflict between the natural environment, environmental preservation and the development of fishing ports, which serve as infrastructure for production and living. I will also discuss on methods necessary for achieving consensus on fishing port development. The example of Saroma Lagoon indicates what research is needed on which to base future academic and technological approaches.

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Many species of Japanese marine molluscs are threatened and facing extinction. The following characteristics are found in this case, 1) many species are threatened, 2) the most common and representative species of the ecosystem in the past are also threatened, 3) species that inhabit estuary and inner bay areas are especially threatened, and 4) species that inhabit sandy and muddy bottoms are also threatened. A total of 433 species of threatened molluscs are listed in the Red Data Books and conservation reports. This fact suggests that the Japanese marine ecosystem is now in danger. Molluscs have a lot of species diversity with ecological characteristics in various habitats, and thus, molluscs are one of the most suitable groups for assessing of the marine ecosystem. I have carried out a conservation movement of molluscs in the tidal flats and salt marshes as an amateur researcher in Kyushu. In this paper, I emphasized the importance of tidal flat and salt marsh bearing a primitive ecosystem. Transplanting molluscs has many problems as a method of mitigation. I suggested that coastal faunal conservation should be achieved by the preservation of habitats. On a project of local development in modern times, it is essential to consider the biodiversity at an early stage of the project. Inventories of important local ecosystems in the aspect of malacology and establishment of sanctuaries are also neccessary. In this respect the demand for participation of amateur researchers on conservation movements of biodiversity has increased recently and their activities would have essential roles in local environmental conservation.

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The heavy oil petroleum flowing out from the disaster stricken oil tanker 'Nakhotoka' in January 1997 widely spread along the coast of the Japan Sea and caused serious oil pollution in the area. A large-scale oil contamination of the beach plant communities was one of the most serious results of the oil spill. The heavy storm and the wavy climate conditions particularly in winter caused the pollution of beach plants repeatedly. The monitoring surveys of the plant communities have been being conducted continuously from January 1997 up to now. In this paper, the method and some results of the survey are described and some proposals are made to promote studies on the effects of oil contamination on plant communities.

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A national census of river and dam lake environments (NCRE) conducted by the Ministry of Construction of Japan has been underway since 1991. Information on the variation in number and habitat use of waterfowl is important in determining the optimum sampling effort necessary for accurately estimating the population density. However, this variation is not sufficiently considered in the census methods used in the NCRE. In this paper, we report the variation in number and habitat use of waterfowl, especially ducks, over short and long temporal scales (daily and monthly changes, respectively) at Takayama dam lake in central Japan. Between December 1998 and March 1999, we counted wintering waterfowl from a small boat and from the lake shore, and analysed the results in relation to the valid range of census methods adopted by the NCRE. General results of the field observations were : (1) the waterfowl assemblage was stable in January and February ; (2) the waterfowl assemblage was stable on any given day and only slightly varied during five consecutive days ; (3) the locations of ducks on the dam lake remained almost the same during both short and long temporal scales ; and (4) terrestrial observations were not useful for counting mandarin ducks and greenwinged teals resting on the surface of the dam lake. These results suggest the following: (1) the winter waterfowl census in central Japan should be conducted in January or February ; (2) the area surveyed in the census should be large enough to encompass the large home ranges seen in several waterfowl species (e.g. common cormorants, mallards and European wigeons) ; (3) routes for line transect and positions for point counts should be chosen carefully when observers count waterfowl on land ; and (4) boat-based observations are recommended for waterfowl censuses.

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Winter waterfowl assemblage structure in nine dam lakes located in Kinki district, central Japan, was analysed in relation to various lake environmental properties, such as water quality, surrounding vegetation and management practices. Most waterfowl recorded in the dam lakes (41.4-100% of the total count) were the mandarin ducks and dabbling ducks, especially mallards, whereas aquatic plant and benthos consumers, such as tufted ducks and European pochards, were few. Important factors affecting waterfowl assemblage structure (richness and diversity) were surrounding vegetation and lake water level, both of which can be controlled by dam managers. The water quality or eutrophic level had little effect on waterfowl assemblage structure. These results suggest that waterfowl assemblage structure in dam lakes is greatly affected by human management. Therefore, dam managers should carefully plan their management activities so that the appropriate environment is maintained for waterfowl assemblages in dam lakes.

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I reviewed the ecology of brachyuran crabs distributed in rivers flowing in central Japan. Ecological information on 20 crab species is introduced. Six life history types were classified according to their distribution in rivers and migration patterns. Regarding types A and B, the distribution of crabs is restricted to brackish areas, without migration (Type A) or with a seaward migration for reproduction (Type B). Regarding types C and D, crabs are widely distributed in the terrestrial environment along rivers, with hatching in the wide area (Type C) or only in the sea (Type D). Regarding type E, crabs grow in the freshwater area of rivers and reproduce in the estuarine area after a downstream migration. In these types, larvae are dispersed in the sea. Regarding type F, crabs complete their life history within the freshwater area, with an abbreviated larval development.
The distribution of crabs tends to concentrate in the estuarine area. Many ocypodids dig burrows in the tidal flat with habitat segregation mainly according to the granularity of substratum, and many sesarminae (grapsid) crabs occur around reed marshes. In the lower and middle regions of the freshwater area, Eriocheir japonica is distributed in aquatic habitats, and three sesarmid crabs (Sesarmops intermedium, Chiromantes dehaani, Chiromantes haematocheir) live in habitats along the river. In the upper reaches, Geothelphusa dehaani occurs in both aquatic and terrestrial environments.
Crabs are important members of the detritus food chain in the tidal area. Ocypodids and grapsids consume particulate organic matter deposited on the substrate and support the decomposition of nutrients by digging burrows into the substrate. In recent years, however, their habitat tends to be lost due to changes in the sediment environment. Construction of weirs also affects their migration process. The loss of natural vegetation around the watershed due to riverworks decreases their habitat.

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High head constructions become serious obstacles for fish in upstream and/or downstream migration. Traditional fishways have some problems of their function such as difficulty for fish to detect the fishway entrance and of their artificial outlook made of concrete. In this paper, we describe an improved type of the head construction, which bears a fishway being harmony with the surrounding landscape by using natural stones, while retaining functional ability to let fish pass over easily. In the process of construction, stones were fixed in the concrete with steel bars, and wooden stakes were inserted in the riverbed to prevent the stones from washing away. In order to make the water flow fit the plan stone arrangement was modified several times during construction. After the improvement, a fish release experiment was conducted using Yamame, Oncorhynchus masou. Ascending rate of the released fish was estimated as high as 52.2%, which indicated that the fishway did not prevent Yamame from ascending. This improved type of head construction could be effective as a nature-oriented river work particularly in steep streams where some head construction are required.

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