Pilot Study in Katagami Bay

Katagami Bay is located in Nagasaki Prefecture on the island of Kyushu which is the southwestern island of Japan (Click here for a map of the region).

This Bay was chosen for our pilot study because the effects of eutrophication are especially evident here. During the summer, strong density stratification separates the water column. This separation allows for the removal of oxygen in the lower water. Hypoxia, as explained in the eutrophication web page is detrimental to both benthic and pelagic organisms.

Circulation in the northern portion of the bay is very slow. This was determined with the use of a 3-D hydrodynamic model. Below, is a simulation of 3-D structure of advection and you can see that circulation is very poor in this upper region.



Animation version (Flash Player 6 is required.)

Because of the lack of circulation, we have placed a small raft seeded with oysters. This raft serves as our pilot study. During the summer months, we plan on aerating this location to increase the amount of DO available to the oysters and benthic habitat. In turn, the added DO in this region can create and oasis of sorts for pelagic organisms and may overall increase the marine fauna in Katagami Bay.



The hope is for the aerated oyster mariculture to produce healthy oysters that will filter the excess N and P and be commercially viable. Healthy oysters like the ones pictured below grow readily in Katagami Bay, if there is adequate circulation.

The complete system

The complete system uses a total of 16 rafts(one raft :8 m x 16 m) placed in a 100 m x 100 m square. Economic feasibility was done and showed that the cost of aeration did not overburden fishermen and that the fishermen would still make a profit selling their oysters. In order to fully remove the excess N and P approximately 5 % of the surface area of Katagami Bay should be covered with these augmented oyster mariculture systems.

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