A Study on the Cultivation, Preservation, and Radiation Hormesis of the Embryos of Invasive Sargassum horneri in Taiwan

• Main Authors: Huang, Roger, 黃怡明
• Other Authors: Chen, Yean-Chang
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/y568es

博士 === 國立臺灣海洋大學 === 水產養殖學系 === 107 === Sargassum horneri is a temperate marine brown macroalga that typically grows up to 3-5 m long in dense underwater forests with a widespread distribution along the coasts of China, Korea, and Japan. Although floating masses of S. horneri have been reported in northern Taiwan throughout the past century, there are no persistent populations of this species in subtropical Taiwan. High summertime seawater temperatures in Taiwan, which regularly exceed 28˚C, are likely a significant factor in preventing S. horneri from establishing persistent local populations. Despite the inability of this species to establish persistent local populations, it is of particular interest for cultivation in Taiwan for its rapid growth rate, large biomass, and economic utility. The reproductive viability of the floating S. horneri that arrives in northern Taiwan each year was examined. Laboratory culture, or in vitro, experiments were conducted on S. horneri embryos to understand the life cycle of the species and the effects of high-temperature on its growth and survival. These experiments provided conclusive evidence that the floating S. horneri arriving on the shores of Taiwan are capable of sexual reproduction and producing viable offspring, but they grow optimally in water temperatures between 18 to 24 °C. S. horneri derived from the floating mass of the species was also cultivated in outdoor seawater tanks, or in situ conditions, in northern Taiwan through a full year and the completion of a reproductive life cycle. This outdoor cultivation experiment demonstrated that S. horneri can be cultivated outdoors in northern Taiwan when it is carefully manually maintained. Experiments were also devised to study methods that allow for less labor intensive cultivation of S. horneri in Taiwan despite the high local summertime temperatures. Two potential strategies for mitigating the effects of high summertime temperatures on the local cultivation of S. horneri were investigated, the induction of high-temperature tolerance in the alga by treatment with low doses of gamma radiation, as well as the utilization of long-term preservation methods that allow embryos of this species to be placed in storage during the summer months and returned to outdoor cultivation in the fall. Radiation hormesis is a phenomenon in which low doses of ionizing radiation can have stimulatory effects on biological systems. We examined the hormesis effects of low-dose 60Co gamma radiation on S. horneri and found that in laboratory in vitro culture, low-dose gamma radiation has the dual effects of enhancing growth and high-temperature tolerance in the treated algae. However, these effects were not observed when the same low-dose gamma ray treatment was applied to S. horneri embryos that were cultivated in situ in outdoor tanks. Analysis of the polysaccharide content of the outdoor cultivated and irradiated S. horneri revealed that the radiation treated algae had significantly higher total polysaccharide content than the unirradiated controls, but the relative composition of the component polysaccharides was unchanged. Two preservation methods for the long-term storage of S. horneri embryos were examined: storage in low-temperature and darkness, and immobilization in Ca-alginate gel. These experiments demonstrated that in laboratory in vitro conditions, embryos preserved in low-temperature and darkness could survive at least 6 months in storage with no negative effects. However, S. horneri embryos attached to cotton ropes and stored in low-temperature and darkness were not viable when transferred to outdoor tank culture after 6 months of storage. S. horneri embryos immobilized in Ca-alginate and immediately cultivated in vitro or in situ without undergoing a low-temperature storage period had no significant differences in growth compared to controls, but embryos immobilized in Ca-alginate and stored at low-temperatures and darkness were not viable in either in vitro or in situ culture. This dissertation shows that cultivation of S. horneri is possible in Taiwan when labor intensive maintenance is employed. However, the application of additional biotechnologies such as low-dose gamma radiation to enhance the temperature tolerance and polysaccharide content of the species, and long-term storage of embryos to avoid the high summertime temperatures can greatly reduce the labor intensive means necessary to cultivate the species and allow for its economic cultivation in Taiwan or other subtropical environments.