Seagrass–Oyster Farmers Interaction Detected by Eelgrass DNA Analysis in Hinase Area of the Seto Inland Sea, Japan

Seagrass beds are one of the most important coastal habitats with high productivity and biodiversity, which can provide various ecosystem services for human beings. Therefore, seagrass beds are often considered as a target for ecosystem restoration. This study demonstrated the contribution of oyster farmers’ long-term activities to eelgrass bed restoration in the Hinase area, based on a DNA analysis of the eelgrass population genetic structure using seven microsatellite markers. The Hinase area was famous for the fishing by coastal pound netting to catch the fish and shrimp migrating to eelgrass beds; however, the fishing was gradually replaced with oyster farming because of the massive loss of eelgrass distribution. The fishermen decided to conduct eelgrass bed restoration, which used a seeding method for several decades even after the oyster farming became their major activity, because they already knew eelgrass vegetation can maintain a better coastal environment for oyster farming as well as coastal productivity for fishing. The farmers collected eelgrass seeds from natural sites with better environmental conditions and then sowed those seeds in the sites where eelgrass beds had disappeared. We collected eelgrass shoots as DNA samples from each of the nine sites where they sowed the seeds and from where the farmers collected seeds. The analysis revealed the farmers’ seeding activity did not disturb the genetic structure of natural dispersal but facilitated the recovery of the eelgrass distribution, suggesting that the eelgrass–oyster farmer relationship in Hinase is a good practice as an ideal ecosystem restoration.