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Distribution of Benthic Organism and Their Remains at the Entrance of Tokyo Bay, in Relation to Submarine Topography, Sediments and Hydrography
Horikoshi, M. (1962). Distribution of Benthic Organism and Their Remains at the Entrance of Tokyo Bay, in Relation to Submarine Topography, Sediments and Hydrography. Nat. Sci. Rep. Ochanomizu Univ. 13(2): 47-122, maps
In: Natural Science Report of the Ochanomizu University. ISSN 0029-8190, more
Peer reviewed article  

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Keyword
    Marine

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  • Horikoshi, M.

Abstract
    The Tokyo Submarine Canyon cuts into the shelf in Uraga Strait which connects Tokyo Bay with the open ocean. The canyon terminates rather abruptly midway in the strait, not reaching the main basin of the bay. The canyon head and the bay are connected by a narrow, corridor-like submarine channel, having a remarkably flat floor. Some 120 dredging stations cover the whole area of the strait together with the bay mouth, ranging from 5 to 600m in depth, including soft bottom areas within the canyon and on the shelf, and also a few hard bottom areas on the shelf-edge. The distribution of the benthos and their remains is influenced both by the water masses and by the submarine topography. The former affects organisms directly as their surrounding medium, and the latter indirectly through water movements and nature of the bottom. Within the canyon, deep sea (bathyal) molluscs were found along with numerous ophiurans, indicating the influence of the cold Intermediate Water. Although benthic assemblages of the shelf-edge are similar to those of the canyon in the predominance of ophiurans, they are rather distinguishable from those of both the canyon and the shelf, including several characterizing species. Hard bottom facies was found at a few stations where a strong current might be inferred. Remains of characterizing species of such a habitat was found on a level bottom at the foot of the slope, indicating the transportation of sediments within the canyon. On the shelf, outer and inner sublittoral regions are recognized, the former being occupied predominantly by polychaetes and pelecypods, and latter by small sized crustaceans. Each region has an individual set of dominant, characteristic and exclusive species. The boundary roughly corresponds to the 20m isobath, which is also that between silty and clean sand. This is clearly seen on the west side of the strait, where flat plaines of different depths are found, while the boundary is less obvious on the east side, where the bottom deepens gradually and the silt-clay content of the sediment is appreciably higher than at the corresponding depth on the other side. Within the submarine channel, characterizing species of both the shelf-edge and the outer sublittoral were found together. This habitat is a peculiar region on the shelf, where the oceanic water enters the bay through the submarine channel beneath the coastal water, and the tidal current is also strong. The higher figures in species and individual numbers might be understood as an edge effect in an ecotone in two senses between two sets of major habitats : the deep- and the shallow sea systems on the one hand, the open sea and the enclosed bay on the other.

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