The effects of water temperature in the sediment and the desiccation period on the growth and survival of transplant seagrass Zostera japonica shoots in mesocosm tank culture

We studied the water temperature requirements and desiccation tolerance of the shoots of seagrass Zostera japonica to determine the conditions for its growth and surviving in mesocosm tanks. All shoots were withered on the artificial shallows set at a depth of D. L. + 40 cm (datum line plus 40 cm) and D. L. + 20 cm until 4 and 9 weeks after transplanting of Z. japonica shoots, respectively. On the other hands, there were 18.5+-1.7, 13.5+-5.8 and 11.8+-4.3 shoots of new lateral shoots at a depth of D. L. + 0 cm, D. L. - 20 cm and D. L. - 40 cm, respectively. At the depth of D. L. + 0 cm, only three shoots developed into reproductive shoots. The upper temperature was 28.6degC at a depth of D. L. + 0 cm. On the other hands, the upper temperature at a depth of D. L. + 40 cm and D. L. + 20 cm was 40.5degC and 34.2degC, respectively. We deduced that the emergence periods on the artificial shallows set of D. L. + 40 cm, D. L. + 20 cm and D. L. + 0 cm could be 17 hours, 9 hours and 2 hours from the temperature change in bottom sediments, respectively. Thus, the one of the factors affecting the critical upper distribution for Z. japonica were the high water temperature and desiccation of bottom sediments.