アサリの生産量が激減した後の緑川河口干潟に生息する底生生物群集の季節変化

抄録

There are sandy tidal flats along the Ariake Sea coast in Kumamoto Prefecture, where 40 to 65 thousand tons of clams, Ruditapes philippinarum, were harvested until the mid-1980s. However, the clam population has collapsed over the past two decades. In the past few years, less than five thousand tons of the clams have been harvested per year. We have studied the population dynamics of several dominant species of bivalves and the benthic community dynamics of the Midori River tidal flats in Kumamoto. The results of population studies of two bivalves, Ruditapes philippinarum and Musculista senhousia, revealed one of the reasons why these populations collapsed on the tidal flats. They suffered high mortality after settling on the substrate. In experimental studies to recover the clam population, sand was brought from the sea floor offshore to the tidal flats, covering an area of 6, 750m² with a 50cm in depth. Abundant benthic communities over 370gWW/m² were formed only in areas where new sand had been placed. Several species of bivalves, including Ruditapes philippinarum and Musculista senhousia, polychaetes and other animals occurred densely one year after the treatment. These benthic animals had low mortality after settling on the new substrate.