Abstract
It is hoped that the Higashimachi district of the Shonan coast will become a significant habitat for coastal plants due to the increasing vegetation area as a result of shoreline advancement. Therefore, this study focused on the migration distance by thalassochory and the composition of drift seeds and existing vegetation to discover the source of seed supply for the Higashimachi district. We released seeds of Tetragonia tetragonoides from five sites and measured the migration distance of the seeds. The composition of drift seeds was examined in the tidal drifts at the Higashimachi district. It was difficult for dispersal of submerged seeds by sea currents to migrate from the Koyurugi and the Tsujido West district of rich coastal vegetation to the Higashimachi district, because the migration length of seeds was short. At the same time, it was found that the migration length of seeds in the mouth of the Hanamizu River was long (maximum 1180m). Therefore, it was possible for dispersal of submerged seeds by sea currents to migrate from the periphery of the mouth of the Hanamizu River to the Higashimachi district. As a result, it was considered that the source of seed supply for the Higashimachi district differed according to the buoyancy period of seeds of the different coastal plants. In addition, it was found that there were 56 species of drift seeds and only five species of coastal plants, such as Carex kobomugi, Calystegia soldanella. These five species were seeds that could float on sea currents for long periods, and were present in the existing vegetation of the Higashimachi district. Consequently, it is considered important to take into account the influence of seed supply from the periphery by thalassochory in order to restore coastal vegetation at the Higashimachi district.
