|Bottom environments of the Ark Shell, Scapharca Broughtoni (SCHRENCK), in Sendai Bay|
Kan-Ho, H. (1966). Bottom environments of the Ark Shell, Scapharca Broughtoni (SCHRENCK), in Sendai Bay. Bull. Tohoku Natl. Fish. Res. Inst. 26: 55-76
In: Bulletin of the Tohoku National Fisheries Research Institute. Suisan-cho Tohoku-ku Suisan Kenkyujo: Shiogama. ISSN 0049-402X, more
Organic matter; Anadara broughtonii (Schrenck, 1867) [WoRMS]; Marine
The ark shell, a commercial bivalves, is distributed in the muddy bottom of the coastal area of Sendai Bay, which is a large mouthed bay facing the North Pacific coast of Japan. The survey was done in 1953 and 1962, to comprehend the bottom environments of the shell bed in the bay. The first survey was carried out in the south coast of the bay, and the second in the whole bay, with the purpose to analyses the composition of the bottom sediments, organic carbon, total nitrogen in the surface layer of the bottom, and the vertical distribution and color of the oxidized layer. The results are as follows. The bottom characters of Sendai Bay are shown as median map in Figure 3. Generally there are fine grained sand areas along the beach, and very fine grained sand and silt areas off shore. The muddy line of the coastal area is about 12 arrow right 4 meters in depth. The central part of the bay has coarse to very coarse grained sand and granule areas. Distributions of the silt contents less than 0.062mm in diameter, the hardness shown by the penetrating depth of the core sampler, and contents of the organic matter, indicate that their higher values exist in silt areas, and the values decrease towards the coarse grained areas. The silt area distributed widely in the coastal area is classified into four regions: Kitakami A region with ample organic matter and oxidized conditions. Kitakami B region where the finest particles settle to the bottom, has more abundant organic matter and the poor oxidized conditions. Natori and Abukuma region have more abundant organic matter and oxidized conditions compared with the other two regions, except for a few points. The ark shell fishery ground corresponds to about these silt regions. The better shell fishing grounds among them are the Natori and Abukuma regions which have abundant organic matter and oxidized conditions. The Kitakami A region is ranked the second. The Kitakami B region is a worthless fishing ground because it has a reductive condition and large depth. In the Natori and Abukuma silt regions, the ark shell is found mainly in these silt areas, but no relation exists between the silt contents of the sediment and the shell numbers. The shell lives crowded near the muddy line zone. From the view point of the ecological action of the shell-bed-constitution, it seem certain that the hydrographical silt-deposition mechanism, the concentration action of the muddy line which effects the settlement of the young, and the more organic matter and oxidized conditions are important factors for luxuriant of the shell.