Growth analysis of eelgrass Zostera marina at Yanai bay [Japan] during spring and summer

The growth of eelgrass Zostera marina in tidal flats was investigated in Yanai Bay, Seto Inland Sea, Japan, from late April to late July 1982. Field surveys were conducted seven times with a marking method at about 15 day intervals. In May and June, the fastest growth of vegetative shoots of eelgrass was observed. The average number of leaves on a vegetative shoot was 4.5 and the plastochrone interval was about 10 days. The average life of a leaf on a vegetative shoot was about 40 days. The growth rates of leaves 10 and 30 days after formation, were 2.5 cm/day and 0.5 cm/day, respectively. The growth rate of rhizomes was about 2cm/day in May. The formation of nodes was synchronized with a loss of leaves by washing away. In generative shoots, neither growth of rhizome nor branching was observed in the period of investigation. Spadices were fromed from late April and became dominant in June. In July, all spadices were washed away and subsequently all generative shoots withered. Our observation suggests that seeds were released together with the spadix when it was washed away, but not scattered one by one.