Study On Techniques And Applications For Zostera Marina L. (Eelgrass) Meadow Restoration

Seagrasses are aquatic angiosperms which have adapted to the marine environment successfully after nearly one hundred million years’evolution from the land. Seagrass meadow ecosystems have been recognized as one of the most important marine ecosystem critical to the health and function of coastal waters for their contributions to the primary production, sediment stabilization, nutrient cycling, trophic exchange and maintaining biodiversity. In the last several decades, global declines of seagrass habitats have occurred within the coastal waters as a result of anthropogenic and natural disturbances, such as human population pressures, irregular commercial fishing practices and aquaculture, sediment and nutrient runoff, invasive species, disease, frequent red tide, and global warming. The losses in the seagrass ecosystem has arisen extensive attention all over the world.Zostera marina L. (eelgrass) is one of the most widely distributed seagrasses on the planet. There used to be abundant eelgrass resource along the coast of Shandong Peninsula in the Yellow Sea in history. Great declines caused by the human activities and natural factors since the 80s of last century had led to great damages on the coastal ecosystem and sharp decreases in fishery resources. Eelgrass restoration projects has been launched for many years all over the world, especially in the developed countries. However, the experience from other coastal areas in the world may not be directly applied locally because of the unique hydrologic conditions of each coastal area. Restoration of eelgrass meadows in China has been tried in recent years. But practical techniques, especially the large scale restoration and construction techniques for eelgrass meadow, have scarcely been documented.In this study, two distinct habitats [open waters in Sishili Bay (SSL), Yantai and semi-closed waters of cofferdam in Ailian Bay (AL), Weihai. Both sites located on north parts of Shandong Peninsula in the Yellow Sea] for Zostera marina L. were successively monitored to investigate the population dynamics and reproduction performance. Seeds collecting techniques was developed in accordance with the characteristic of the eelgrass meadows in the sea area. The optimum conditions for seeds storage and germination were also studied. Seedlings cultivation techniques, seedlings transplanted apparatus and an effective adult shoots fixing method was developed for eelgrass meadow restoration. Clam seeding techniques were also developed using Ruditapes philippinarum as seeds carrier. Using the techniques developed in this study, about 18000 m2 of Z. marina meadows were restored in Furong Island waters in Laizhou Bay. The successful application of these techniques not only provide practical guide for the Z. marina meadow restoration, but also provide valuable references for other seagrass species (especially Zostera) restoration. The main results are summarized as follows:1. The above ground biomass and shoots height of Z. marina inhabits in north coastal waters of Shandong Peninsula varied significantly with seasonal succession. There were significant differences of mean maximum above ground biomass (SSL 487.6g DW/m2, AL 754.8g DW/m2), shoots height (SSL 69.9cm, AL 107.4cm) and shoots density (SSL 273.2shoots/m2, AL 364shoots/m2) between the two distinct habitats (p<0.05). The mean maximum reproductive shoots density was significantly higher in semi-closed cofferdam in Ailian Bay (109.2 shoots/m2) than that in open waters in Sishili Bay (69 shoots/m2), but seed produced by Z. marina in open waters was significantly larger than that produced in semi-closed waters indicated that open water seeds have advantage in recolonization of new spaces.2. Sexual reproduction of Z. marina in the north coastal water of Shandong Peninsula usually takes place from April to August. It usually develops its reproductive shoots from late April to early May (seawater temperature from 11.4 to 13℃) and flowers in mid-May (14.5-15℃). Its seeds usually ripen from mid-June to early July (17.6-19.2℃). The optimum period for harvesting the reproductive shoots usually begins in mid-July (20℃), but field checking is necessary. The optimum time for harvesting usually lasts for 2-3 weeks. From 2009 to 2013, using the suspended in situ method,176,000,421,000,364,000,1,041,000 and 1,091,000 seeds were successfully collected respectively. The grand mean yield was 386 seeds per liter of reproductive shoots over the five years.3. The Z. marina seeds are strongly desiccation sensitive. Survival rate of the seeds was significantly affected by relative humidity, exposure temperature and time (p<0.001). Significant interactions between relative humidity and exposure temperature (p<0.001), relative humidity and exposure time (p>0.005), exposure temperature and time (p<0.001) were detected. Significant interaction among the three factors was also detected (p<0.001). The moisture content of fresh ripe seeds was about 40.6%. When exposed to temperature of 25℃ and relative humidity of 50%, the moisture content of the seeds decreased to 27% approximately and mortality reached nearly 50%. Interaction between salinity and temperature significantly affected the cumulative germination rate during the storage of seeds (p<0.05). The water temperature of 4℃ and salinity of 44.5psu reached the lowest cumulative germination of about 6.7% among the tests. The germination was significantly inhibited at lower temperature and higher salinity.4. The germination rate of the seeds was significantly affected by salinity and temperature (p<0.001). The germination rate reached about 83.3% in 8 weeks at 14℃ and 5psu, which was the highest among the tested groups (p<0.001). Vernalization had significant effect on the seeds germination rate (p<0.001), the results of the test showed that seeds vernalized at 4℃ for 50 days reach the highest mean germination rate of 55.3%. Seeding depth had effect on the seedling establishment rate of Z. marina seeds. No significant difference was detected among the seedling rate of tested depth 0.5-1 cm,1-1.5cm and 2-2.5cm, but the seedling rates of the above three depths were significantly higher than that of 3-3.5cm and 4-4.5cm (p<0.01).5. After being vernalized and seeded into the bay sediment (from Sishili Bay) at the depth of 2cm approximately, with seawater salinity 8psu at the first 3 weeks and a gradual increase to 30psu,76 thousand seedling shoots were successfully cultured after 110days. The mean height of the seedling was 16.3cm with the maximum 24cm. Seedling cup transplanting apparatus was successfully developed and put into practice which proved very effective.6. To make good use of the waste vegetative shoots removed from the cofferdam, the innovative "inverted T style fixing method" was successfully developed which led to a high survival rate of 83.8% and could regenerate quickly the next year.7. An innovative clam seeding techniques were also developed using Ruditapes philippinarum as seeds carrier. Seedling establishment rate was about 24.7% after being seeded for five months, which was significantly higher than that of the seeds broadcasted on the surface of the sediment 7.7%(p<0.01).