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

点击翻译按钮获取中文摘要

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.