The Nagasaki Prefectural Institute of Public Health and Environmental Sciences and JAMSTEC (Japan Agency for Marine-Earth Science and Technology, of Yokosuka City, Kanagawa Prefecture) conducted an in situ oyster culture experiment in an enclosed inner bay and found that their new technique offers an economically sustainable method of cleaning water affected by eutrophication (an excess of nutrients). The purification technique reduces substances such as nitrogen and phosphorus in the water by inducing oysters to absorb them as nutrients, eliminating the need to provide them other feed. This method can promote the fisheries and other regional industries, and clean up the sea at the same time.

Nitrogen and phosphorus are essential for many organisms to grow. They are also used as fertilizers in agriculture, and flow into bays from waterways, where they promote the growth of fish and shellfish, and return to land again when marine products are fished out of the sea. But an overabundance of nutrients causes eutrophication of the ocean, oxygen deficiency, and red tide--problems that inhibit the growth of marine life.

Although oyster farming without providing direct feed is an efficient way to recycle the excess nutrients in sea water, oyster stocks are sometimes decimated from oxygen deficiencies under conventional methods. This experiment used aeration hoses placed on the seafloor below the oyster bed to supply air to the oysters. By using the aeration system for the three months of summer that are typically the worst months for water quality, the experimenters ensured oyster survival and improved growth.

This method of oyster farming can provide a sustainable way to clean seawater if the profits from increased harvest exceed the equipment and electricity costs for aeration. This was the world's first in situ test of a method that promotes oyster farming and helps clean up the seabed and seawater at the same time. Nagasaki Prefecture and JAMSTEC are jointly applying for a patent on this technique. They plan to repeat the experiment three times by March 2006 to assess¡¡the variability in effectiveness under changes in the weather and other environmental factors, and quantify the efficiency in water purification.


http://www.jamstec.go.jp/

Posted: 2004/07/27 11:56:18 AM
Japanese version

TAG Ecosystem , Food/Water , University/Research institute