Eelgrass (Zostera marina L.) meadow , which have important ecological functions in coastal and estuarine areas, are distributed widely in Japan. Although the area of eelgrass meadow has recently increased in the Seto Island Sea, overall there have been declines in our country over the past few decades. Eelgrass restoration was shown to recover and conserve the ecological functions that had been or will be lost by the disappearance of eelgrass meadows. Methods for eelgrass restoration have been presented in guidelines published in the past decade, and new findings of eelgrass growth and restoration have been reported.
In this study, the knowledge and recent new findings of eelgrass growth and restoration were investigated. In addition, a strategy for resource (seeds or shoots) investment was considered using a simple mathematical model. The investigation showed that there are environmental factors relating to the sexual and/or vegetative propagation of eelgrass. It means that eelgrass meadows can grow only by sexual or vegetative propagation or by both propagations, i.e. there are three types of eelgrass meadows.
The consideration of strategies showed that making plans for resource investments to gain maximum success, or the expected success and the spread of risks, is dependent on the success rate of eelgrass restorations.
Because the type of eelgrass meadow and investment strategy determines the location of the recipient site, the improvement method for its environment, and the planting method have to be set as the first step in eelgrass restoration. In this study, determination of flows at the recipient site, the environmental improvement method, and the planting method were proposed for types of eelgrass meadow grown only by sexual or vegetative propagation or by both propagations. In addition, future studies were indicated.
The proposed methods for eelgrass restoration are expected to be applied in the future.
Key words: Eelgrass (Zostera marina L.) meadow, Restoration, Conservation, Recipient site, Planting methods, Investment strategy