| Sargassum vachellianum belonged to Phaeophyta with the shape of the tree and the largest sizes of 160 cm. As the endemic to China it was an important part of seaweed beds and excellent specie of artificial seaweed beds construction. It was one of the important economic algae which had potential economic value and could be used to extract of seaweed polysaccharides, alginate, medicine and industrial raw materials.In recent years, due to over-exploitation of tourism resources and large-scale farming of mussels, coastal waters became serious eutrophication and S.vachellianum bed ecosystem in Gouqi Island moderately degraded,belonged to classⅢ of degenerate levels, general health status, the wildlife resources damaged severely.On the basis of technology of building of S.vachellianum artificial reef,mariculture of S.vachellianum and its effects on the factors of water environment in Gouqi Island were studied in this paper. Firstly, we studied suitable environmental conditions on growth and photosynthesis of S.vachellianum from temperature, light and salinity in the laboratory.Secondly,according to optimal growth conditions of S.vachellianumm, artificial breeding of S.vachellianum in hatchery and large scale cultivation in open ocean was done.The techniquesystem of artificial breeding and cultivation in open ocean of S.vachellianum were established.Thirdly, on the basis of artificial breeding and cultivation in open ocean, large scale cultivation of S.vachellianumum and its effects of ecological restoration were studied, so as to In order to restore S.vachellianum bed and provide a theoretical basis and technical support forthe use of macroalgae to repair marine ecological environment and curb eutrophication.The main results are as follows:1. Effects of different environmental factors on the growth and photosynthesis of Sargassum vachellianumEffects of different temperature, light intensity and salinity on specific growth rate, dry weight, photosynthetic pigment content and photosynthetic oxygen evolution activity in S.vachellianum are studied. The result showed that the effcts of temperature, light intensity and salinity environmental factors on the growth, photosynthetic pigment content and photosynthetic oxygen evolution activity of blades in S. vachellianum were significant respectively. The suitable temperature, light intensity and salinity for S. vachellianum were 15~20℃, 20~60μmol·m-2·s-1 and 20~40, respectively. The optimal growth temperature and salinity were 20℃ and 30 respectively, and the maximum specific growth rate reached up to 5.80%d-1. When the temperature was above 25℃, or the light intensity was higher than 200μmol·m-2·s-1, or the salinity was less than 10 or higher than 50, the blades would stop growing almostly and became pale, soft and rot in two weeks later. The S. vachellianum could accumulate more photosynthetic pigments when the temperature was in 10~20℃ or the light intensity was at 20~60μmol·m-2·s-1 or the salinity was at 20~40. When S. vachellianum were coultured at 20℃ with 100μmol·m-2·s-1 and salinity 30, the blades photosynthetic oxygen evolution reached the highest, about 258.50 μmol·mg-1·h-1. Compared with the lower light intensity, the higher light intensity inhibited the photosynthetic oxygen evolution activity insignificantly. The results provided theoretical bases for conservation of S. vachellianum resource and restoration of S. vachellianum bed.2. Studies on Sargassum vachellianum large-scale breeding technologyThis paper mainly studied the large-scale seeding technology optimization of S.vachellianum and breeding techniques in natural sea area. Gathering mature algae from sea area then after cultivation, ripening and diffusing fertilized egg, we collected 9.208 million fertilized eggs. After spraying the collected fertilized eggs on floor slab, coir rope and plank. We found that coir rope seedling effect is best, and the plank to take off seedling is most serious. Fertilized eggs spraying 10 days later, the seedling emergence rate of these three substrates were 85.5%, 80.2%, 91.3%. The seedling is brown and acicular, and the average plant height is about 1.3 mm. The three attached seedling density is higher and stable in the first 20 days, and the seedling density of plank is highest. The average plant height is 8.2 cm, and have significant differences with other groups(P < 0.05). But the seedling growth was slow, and the average specific growth rate is only about 5.5%·d-1. The 30 th day, seedling appeared branches, and the growth rate increases to 1.6 times then the first 20 days. The coir rope seedling plant height is the highest, and have a significant difference with the other two groups(P < 0.05). The seedling density were significantly reduced, and the seedling survival rate were 83.6%, 79.7% and 75.6%. The 60 th day, the seedling density and average plant height of coir rope is the largest, and have significant differences with other groups(P < 0.05). After put the floor slab(algal reef) and coir rope with seedlings into sea for farming, we found that seedlings grow faster in wave flow in sea area. After four weeks, the average plant height is 98.7mm and 103.1 mm, and reached 1.5 times then the control group. However, the seedlings on coir rope were taken off seriously. Thus, the algal reefs were more suitable for large-scale farming and they were also as an ideal material for repairing and reconstructing of algae bed. The results provided theoretical bases for large-scale cultivation and building of S. vachellianum bed.3. The scale farming of Sargassum vachellianum on Gouqi island and its effects on the factors of water environmentThe scale farming of S.vachellianum on Gouqi island and its effect on the factors of water environment were studied. The results showed: the suitable water depth for S.vachellianum were 1.5m~2.5m, the optimal water depth is 2m; Breeding algae could grow faster and mature earlier than wild algae in spring and autumn,it began to decay in summer. Two kinds of algae had the highest specific growth rate which were 6.8%·d-1 and 5.9%·d-1. In 2014, the IP、IN、TN、TP and COD concentration reduced compared with last year,except for the 1st and 7th station.DO concentration and SD increased by 4.52% and 8.09%, COD and Ch-a reduced by 18.75% and 43.51%, the Ch-a concentration is very low with the highest value of 1.55μg·L-1. Compared to 2011, the density and height of S.vachellianum increased significantly in 2014, the S.vachellianum field area increased from 1,500 m2 to 75 million m2. The water quality was improved significantly and the S.vachellianum bed got certain recovery. The results provide a theoretical basis for cultivation of S.vachellianum and ecological restoration of the marine environment. |
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