Improvement Effect of Clam Habitat by Fertilizers and Sealing Plates

Abstract

The catch of Manila clams in Japan has drastically decreased recently. It is necessary to promote the growth of benthic microalgae, which is their main feed, for the reproduction of tidal flats where clams grow. In this study, we applied dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and Fe-eluting fertilizer to tidal flats surrounded by a sealing plate to prevent fertilizer outflow. We found that DIN and DIP in pore waters and chlorophyll a in the surface sediments almost increased in concentration at fertilizing sites. However, periods of nutrient elution from the fertilizer were considered to be less than half a year In addition, the weight of clams collected from the 1600g fertilizing site was significantly greater (t-test, p<0.05) than that from the control area. Consequently, the total weights of clams collected from the control site and fertilizing sites increased to approximately 7.2 and 10.4-12.6 times greater than the initial weights, respectively, four months after the experiment started. In conclusion, using a combination of fertilizers and sealing plates is effective for increasing the weight of clams inhabiting the tidal flats.