‘428
KOHMAN Y. ARAKAWA
faecal matter on a dry basis in 11 days, when they covered an acre of
the .bottom. Besides, Verwey (1952) calculated that Cardium in
Waddenzee deposits 100 000 metric tons (dry weight)/year and that
Mytilus deposits between 25 000 and 175 000 metric tons annually.
The effects of bulky biodeposits by marine organisms upon marine
environmental con.ditions have been noticed by some Japanese workers
PERMANENT
SEDIMENTS
DETRITUS FEEDERS
BACTERIAL DECOMPOSITION
Fig. 30. Biodeposition cycle in the York River estuary (after Haven and MoralesAlamo, 1966).
in the case of oyster culture beds in Japan, where the oysters are commonly cultured by the hanging method. I n this method there is an
unusually high estimated density of 420 000 oysters/200 m2 or 420 000
oysters/200 m2 x LO m2, because the middle stratum of water is used
for culturing. An instance only remotely comparable to this in Japan
is that of the pearl oyster beds. Consequently, recent studies on
oyster and pearl oyster culture beds have been focused on the organic
KOHMAN Y. ARAKAWA
faecal matter on a dry basis in 11 days, when they covered an acre of
the .bottom. Besides, Verwey (1952) calculated that Cardium in
Waddenzee deposits 100 000 metric tons (dry weight)/year and that
Mytilus deposits between 25 000 and 175 000 metric tons annually.
The effects of bulky biodeposits by marine organisms upon marine
environmental con.ditions have been noticed by some Japanese workers
PERMANENT
SEDIMENTS
DETRITUS FEEDERS
BACTERIAL DECOMPOSITION
Fig. 30. Biodeposition cycle in the York River estuary (after Haven and MoralesAlamo, 1966).
in the case of oyster culture beds in Japan, where the oysters are commonly cultured by the hanging method. I n this method there is an
unusually high estimated density of 420 000 oysters/200 m2 or 420 000
oysters/200 m2 x LO m2, because the middle stratum of water is used
for culturing. An instance only remotely comparable to this in Japan
is that of the pearl oyster beds. Consequently, recent studies on
oyster and pearl oyster culture beds have been focused on the organic