Abstract

Growth and survival of the hard shelled mussel spat were investigated to confirm the possibe spat culture in seawater pond from September 2014 to April 2015. Also, we measured simultaneously environmental factors including water temperature, salinity, dissolved oxygen, pH, DIN, DIP, chlorophyll a, and abundance and dominant species of phytoplankton in seawater pond every month. Ranges of water temperature and salinity were <TEX>$4.0-23.4^{\circ}C$</TEX> and 18.8-25.2 psu, respectively, which were rather lower than the reported optimal level. Monthly measured survival rates in all the spat cages were over 90%. Concentration of chlorophyll-a and abundance of phytoplankton were very high, and dominant species phytoplankton were cryptomonads and nanoflagellates. These dominant species were considered to be good food organisms for the bivalve spat. The experimental cage stocked 100 individuals per basket (<TEX>$2,700ind.\;m^{-2}$</TEX>) hanging in bottom of seawater pond revealed the highest growth in shell height (<TEX>$7.63{\pm}4.65mm$</TEX>), but all experimental cages stocked below 200 individuals per basket (<TEX>$5,400ind.\;m^{-2}$</TEX>) did not show statistically significant difference. We may expect that seawater pond would be one of the best culture ground for bivalve spats when appropriate measures are available.