The amount of bottom-dwelling organisms found near a controversial reclamation project in Isahaya Bay in Nagasaki Prefecture has dropped drastically following a reduction in the amount of oxygen in the water over the summer, the Environment Ministry said Tuesday.
The data is the first to link a drop in benthic, or bottom-dwelling organisms, to oxygen deprivation in Isahaya Bay.
The study checked five points in the bay at varying distances from the nearly 7-km-long seawall that sealed the interior of the bay off for reclamation purposes in 1997. From June to August, every point surveyed showed a drop in the number of benthic organisms as well as the amount of dissolved oxygen in the water, which life requires.
The survey spot nearest the seawall dropped from 916 organisms logged in June, to 79 in August, while at a point roughly 4 km from the wall, 2,070 organisms were recorded in June and none were found in August.
The study was conducted to shed light on the possible effects of the reclamation on the bay environment.
Past government data indicates that the number of bottom-dwelling organisms have fallen in the summer before, but there is no other data linking it to reduced oxygen levels in the water.
A ministry study also released on Tuesday covering the whole Ariake Sea, which contains Isahaya Bay, yielded similar results.
Dissolved oxygen levels at sea bottom near the reclamation project were found to be below the 3 ml per liter recommended by Fisheries Agency-related groups.
Ministry officials said this does not explain the poor seaweed harvest that ravaged the Ariake Sea last season. Farmers were unable to cultivate anywhere near normal levels of "nori" seaweed, which is used to wrap sushi and for which the area is well-known.