Study on the sea-drift seed dispersal mechanism and the distribution characteristics of seashore plants growing on the banks of Osaka Bay

本研究的目的是阐明引起海滨植物种类数量变化的可能因素，影响植物分区结构的可能因素，并分析海洋漂流种子的传播机制，以确定大坂湾特有的分布特征，并帮助寻找最有效的方法来保护那里的植物生命。通过使用刺藤（Puncture Vine）的种子进行漂移种子分散，刺藤是一种现在处于灭绝危险的本土植物。种子不一定到达海岸，但在种子漂浮限度内汇编的测试结果表明，散布模式因若干不同的物理条件而沿沿着地区不同。首先，对于天然的、未受影响的海滩，种子被冲上岸的可能性取决于水边海滩与海湾水流的倾斜角度。其次，对于由人工结构如码头组成的海岸线，这些建筑物通过影响海流而阻碍了种子的传播。第三，尽管刺藤种子的漂浮能力较低，但有相当一部分是通过粘附的方式分散的。最后，考虑到目前的分布特点、环境、人类和海岸的位置效应，探讨了保护和恢复大坂湾海岸植物生命的可能途径。需要立即采取防腐措施的海滩位于淡路岛的北方、从仙南市到汉南市的地区以及Kihoku地区，这是面向大坂湾的沿海地区的潜在种子供应源。与此同时，位于须间、兵库和大坂府仙南地区的海滩预计未来将保留相同的植物生命。需要采取一些保护行动的沿海地区是淡路岛南部和西宫地区，在这些地区，海滩的保护和利用可以成功地结合起来。

The objective of this study was to clarifying possible factors causing change in seashore plant species numbers, possible factors affecting plant zoning structure, and to analyze the sea-drift seed dispersal mechanism in order to ascertain the distribution characteristics particular to Osaka Bay and assist in finding the most effective way to preserve the plant life existing there.Field tests on sea-drift seed dispersion were conducted by using seeds of the Puncture Vine, a native plant now in danger of extinction. The seeds did not necessarily reach shore, but test results compiled within seed floatation limits indicated that dispersal patterns varied along coastal areas depending on a number of different physical conditions. Firstly, for natural, untouched beaches, the possibility of seeds being washed ashore was determined by the inclining angle of the beach at the water's edge to the bay current. Secondly, for coastlines comprising of artificial structures such as piers, those constructions hampered the seed dispersal by affecting the sea current. Thirdly, despite the low floating capability of puncture vine seeds, quite a few were dispersed by means of adhesion.Lastly, taking into consideration present distribution characteristics, environmental, human, and positional effects of the seashores, possible ways to protect and rejuvenate seashore plant life in Osaka Bay were examined. Beaches requiring immediate preservative action lie in the northern part of Awaji Island, the area ranging from Sennan to Hannan Cities, and the Kihoku region, a potential source of seed supply for the coastal areas facing Osaka Bay. Meanwhile, beaches such as those located in Suma, Hyogo and the Sennan region in Osaka Prefecture, are expected to retain the same plant life in the future. Coastal areas in need of some preservative action are on southern Awaji Island and in the Nishinomiya area, where both preservation and utilization of the beaches can be successfully incorporated.