Crushed oyster shells reduce mud shrimp (Upogebia major) populations and enhance Manila clam (Ruditapes philippinarum) recruitment in Korean tidal flats

Abstract

In tidal flats, the mud shrimp (Upogebia major) is a key competitor of bivalves such as the Manila clam (Ruditapes philippinarum), resulting in significant losses in clam productivity due to high-density settlement and burrowing activity. Traditional control methods, including mechanical disturbance and chemical pesticides, have proven ineffective and caused environmental issues. This study investigates the effectiveness of using crushed oyster shells as an eco-friendly and resource-recycling approach to control U. major populations and improve the sediment environment for Manila clam spat recruitment on a tidal flat in Boryeong, Korea. Crushed oyster shells (5 cm size, 15 cm thickness) were placed in a 600 m2 experimental plot with high mud shrimp density. Over a sixmonth period, the number of mud shrimp burrows in the treatment plot decreased by 86.7-99.7 % compared to pre-treatment levels and remained significantly lower than in the untreated control. Sediment analysis showed that the application of oyster shells increased gravel and sand content, shifted the sedimentary facies from sandy mud to gravelly mud, and maintained acid volatile sulfide concentrations well below national environmental standards. Manila clam spat recruitment increased in the treatment plot, reaching 1067 clams/m2 in October, approximately double the control, and survival rates remained consistently high (97-100 %) compared to the control. These findings show that crushed oyster shell successfully reduces mud shrimp settlement, improves sediment conditions, and enhances both recruitment and survival of Manila clam spat, offering a sustainable and environmentally friendly way to manage mud shrimp populations and restore bivalve productivity in tidal flats.