Abstract
Seasonal changes of Zostera marina L and physical environment factors (underwater irradiance, Sandy
bottom quality etc.) were examined off Miya in the Mikawa Bay, Aichi Prefecture, from 2000 to 2001 Japan.
Z. marina forming seagrass beds grew densely from February to June, and declined from July to October.
While a large number of juveniles geiminated from their seed started to appear toward the middle of
October, and Z. marina grew densely again in the following spring. Most of the Z. marina off Miya was annual.
Vertical distribution range of Z. marina beds were from D.L. +0.5m to -1.6m depth. From the site irradiance
conditions in the seagrass bed, the deepest bottom of Z. marina possible growth was estimated to be
D.L.-1.8m. The high temperature in the summer was the important cause that the Z. marina beds were
decreased. Surface layer of the bottom was reductive conditions enough to germinate. These observations
suggest that Z. marina of annual plant requires calm environmental conditions as one of the required suitable
conditions for successful seagrass bed formation.
