Characterization of germination and seedling production of Zostera marina and Z. Caulescens

Efficient recovery of seed germination and growth were investigated to determine the optimum combination of salinity and temperature in two seagrass species, Zostera marina L. and Z. caulescens Miki. Flowering shoots of Z. marina were collected at the depths of 0.5–3 m from Shin-nase in Sagami Bay and Nami-ita in Okirai Bay, while those of Z. caulescens were collected at the depths of 3–8 m from Tenjin-jima in Sagami Bay and Nami-ita in Okirai Bay. Seeds of Z. marina obtained from fructified spadices showed germination induction by soaking and keeping them in freshwater under dark condition at 20°C for 24 hours. This pretreatment improved germination rate by 90%. When the seeds were kept in above 5 psu, the germination rate was significantly dropped to less than 30%. While the germination rate of Z. caulescens was above 60% by the pretreatment with freshwater or low salinity less than 10 psu under dark condition at 20°C for 24 hours.// The minimum irradiance requirement for the growth of seedlings of Z. marina and Z. caulescens was found to be in 12 and 5m mol photons m-2 s-1, respectively. The effects of salinity and irradiance on seed germination rate were different in these two seagrass species. The difference in the effects clearly reflect the natural habitat conditions in which the plants grow