抄録
Tidal flats in Imazu and Kafuri Bay in Fukuoka Prefecture, Japan, were well known as the nest-sites of horseshoe crabs, but their nesting has declined because of water and sediment pollution of the bay. To rehabilitate the polluted beach in the tidal flat, placement of fresh sand on the beach was performed by Fukuoka City, resulting in an increase of nesting of the horseshoe crab. We compared the factors that potentially affect nesting at Imazu and Kafuri beach : morphology, exposed time, grain-size distribution, water content, oxygen concentration, and redox potential. The elevation of the beach was higher at Imazu than at Kafuri, leading to a longer exposed time at Imazu than Kafuri. This induced low water content, and high oxygen concentration and redox potential at Imazu compared with Kafuri though the grain-size distribution and organic matter were almost the same at both beaches. We suggest that sand placement is an effective procedure to rehabilitate nesting sites of the horseshoe crab in terms of exposed time of the sites, water content, oxygen concentration, and temperature.
