The isolating property of enclosed bays, which cuts off the connection with the open sea by the topographical constriction at the bay mouth, affects strongly the cultural environment in the bay not only positively but also negatively. In order to prevent the retrogradation of culture farm and to maintain the sound cultural environment, it needs to understand quantitatively the physical processes in enclosed bays. In this paper, the observational results in Yamada Bay of Sanriku Coast are introduced as one of examples of oyster culture farm developed in many enclosed bays. The steady process and the transitory process in the onclosed bay play respectively important roles in formation and change of the cultural environment. The tide is weak in the enclosed bay, but steadily acts to form the cultural environment over a long term. On the other hand, the actions such as an intemal Seiche (an intemal standing wave) and the Kyucho (a stomy current) tend to be overlooked because of transitory event, but their energies disturb suddenly the cultural environment which has been formed by the steady process. Further the interaction between the steady process and the transitory process is also important to form the cultural environment in enclosed bays.

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Live and formalin-fixed clams of a shell length of 26-28mm were buried at an approximate depth of 3cm in the substratum of the Banzu tidal flats in Tokyo Bay. Surveys on the relationship between the number of Japanese littleneck clams retained in test beds and changes of the bottom sand level due to wave action were conducted from September 1994 to March 1995. In the autumn and spring, the number of live clams remaining in each test bed was higher than that of formalin-fixed clams. The number of live clams was found to be lower in the winter than in the autumn and spring. Cumulative retention rates were 0 to 40% for live clams and 0 to 48% for fomalin-fixed clams. The bottom level remained almost unchanged when the Shields parameter was less than 0.12, slight substratum deposition was seen when the Shields parameter was between 0.12-0.16, and erosion occurred when the Shields parameter was greater than 0.20. Generally, the number of formalin-fixed clams and weakened clams tended to decrease when the erosion of the bottom surface exceeded 2cm and the Shields parameter was greater than 0.20. Even healthy clams, which are capable of burrowing deeply into the substratum, will decrease gradually in number where the Shields parameter is occasionally in excess of 0.2.

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In this paper, the effect of wave direction on local scour at rectangular columns was investigated. Local scour depth around rectangular column is variable in association with the shape of column and angle of column oriented to the direction of waves. In general, the point of maximum scour depth occurred at the comer of the column when column width oriented 90 to the wave direction. At another angle of orientation, the point of maximum scour depth tended to move to the cross-sectional comer perpendicular to the wave direction. As a result, it shows clearly that the effect of wave direction on scour depth was variable in association with the shape of column, referred to column thickness, and also the angle of orientation. The orientation factor, Kθ which accounts for the effect of wave direction in the scour depth equation, was examined. In conclusion, the effect of wave direction should be considered as a factor for estimating scour depth of artificial reef.

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Decline of afforested Ecklonia cava community by grazing of herbivorous fish Siganus fuscescens was studied on the coast of Hamaoka, Shizuoka Prefecture, Japan, during a period from May 1998 to November 1999. About 400 individuals of 3-years old E.cava were grazed their laminae during September to October 1999, and about 2,800 young individuals were grazed their laminae, only left their stipe from October to December. Because the fish bites basal parts of Ecklonia laminae, damage to the thallus is serious though the fish grazes small amount of plant body. Grazing by S. fuscescens was observed on and after June in 1998, while in 1999 grazing was seen on and after August. Rise of seawater temperature was earlier in 1998 than in 1999. This observation shows that grazing activity was affected by change of water temperature. Effect of grazing pressure by herbivorous fish on the growth of afforested E.cava community is clearly demonstrated from our observation.

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A macrobenthic survey was conducted around the Ishikari Bay New Port in west Hokkaido, Japan, to describe the community structure of macrobenthos associated with sedimentary conditions. A total of 70 species were collected at 29 stations using a Smith-Mcintyre grab sampler in September 1998. Dominant species were three juvenile bivalves (Mactra chinensis, Psendocardium sachalinensis, Megangulus uenulosos), six polychaetes (Goniada maculata, Spiophanes bombyx, Spio filicornis, Nephtys caeca, Magelona japonica, Glycera capitata), two echinodems (Scaphechinus griseus, Echinocardium cordatum), and four amphipods (Phoxocephalidae sp., Ampelisca brevicornis, Urothoe grimaldii, Corophium sp.). Distribution pattems of the dominant species changed with feeding type, depth and sediment particle size. Suspension feeders occurred at 2-17m depth in well-sorted mediate to fine sand. Deposit feeders occurred at 17-23m depth in well-sorted fine to very fine sand. Carnivores occurred at 7-17m depth in well-sorted mediate to fine sand and at the mouth of Ishikari River in unsorted fine to very fine sand. Tube-building deposit feeders occurred at the port in unsorted fine to very fine sand. Facultative deposit feeders occurred throughout the whole survey area, except at the river mouth. At 2-17m depth, suspension-feeding bivalves, which have a planktonic larval period of 2-4 weeks, occurred densely on the northeast side of the port, and suspension-feeding amphipods which undergo direct development, were the dominant species on the southwest side of the port. It was suggested that macrobenthic communities around this port are strongly affected by hydrodynamic conditions, which influence the food supply to the animals and their recruitment.

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