Evaluation of substrates for constructing beds for the marine macrophyte Zostera marina L.

• Silt and clay in sediment enhanced the anchorage of eelgrass roots to sediment.
• The silt and clay content most favorable for eelgrass root anchorage was 15–20%.
• Dredged sediment and fly ash were useful silt and clay sources for construction.

The selection of substrate material is a critical factor for successful construction of eelgrass beds. We evaluated the effects of different proportions of silt and clay particles (<75 μm) in sediment on the anchorage of eelgrass roots using natural eelgrass bed sediment and mountain sand as basal materials, and silt and clay particles separated from natural sediment, dredged sediment or fly ash as the silt and clay component. We evaluated the anchorage of plants by their resistance to an uprooting force. Silt and clay particles were important to the anchorage of eelgrass roots. Complete removal of silt and clay particles from natural eelgrass bed sediment clearly reduced the uprooting resistance by about half. The optimal silt and clay content for eelgrass root anchorage was 15–20%. The addition of dredged sediment or fly ash to mountain sand enhanced the uprooting resistance of eelgrass plants.