An abnormal presence of phytoplankton in Kyushu's Ariake Sea has reduced the amount of nutrients available for seaweed, lending credence to the theory that this was a major factor in this year's disastrous nori harvest, an Environment Ministry study showed Tuesday. However, officials stopped short of saying large amounts of phytoplankton caused the poor harvest.
The study indicates an inordinate proliferation of algae that, like seaweed, consume nitrogen and phosphorous. Inorganic nitrogen and phosphorous levels in the water were drastically below ideal levels for producing seaweed, the officials said.
An abundance of chlorophyll as well as oxygen were observed in the seawater, also pointing to an abnormal presence of phytoplankton similar to levels seen during times of red tide outbreaks, the study said.
It also found a decrease in the amount of benthic, or bottom-dwelling sea life, in comparison with data from nearly three decades ago. While a study in summer 1972 found between 2,000 and 5,000 organisms per sq. meter, the February study found an average of less than 2,000 -- the minimum observed anywhere in the sea 30 years ago.
The reason behind the rise in algae and the reduced numbers of benthic sea life was not clear, officials said.
The areas that showed the highest phytoplankton levels and the least benthic organisms were not necessarily concentrated around the controversial reclamation project being carried out in Isahaya Bay, officials said.
Fishermen and seaweed growers have blamed the project for the worsening of the Ariake Sea environment and have been lobbying for the opening of the dike that closed part of Isahaya Bay off from the sea in 1997.
While the survey only contains data for Feb. 23 and 24, it is probably representative of the water quality during the seaweed harvesting season of late last and early this year, officials said.