Surveys Of Natural Populations And Artificial Breeding Of Sargassum Thunbergii

An annual ecological investigation was conducted related to the seasonal pattern of Sargassum thunbergii, a dominant species distributed along the coast of Lidao Bay, Rongcheng, China. The local S. thunbergii population entered the maturation period from early June to mid-August, when seawater temperature was 14.4- 25.1℃. Both the accumulation of temperature and the increase of photoperiod promoted reproduction of the S. thunbergii population. Primary branches reach the maximal length and biomass during the maturation stage and the mature thalli in 20- 39.9 cm had a relatively high frequency. Subsequently, branches reduce drastically due to senescence and shedding, with minimal branch length and biomass in November. The tidal position had significantly affected on the thallus length and biomass that the thalli from the low tidal position were obviously superior to that from the middle tidal position and the high tidal position both in length and biomass. The frequency and biomass in length hierarchies varied greatly around the maturity.In order to conduct artificial seedling production of S. thunbergii, we observed the zygotes release, the rhizoids development and the attachment of germlings, and conducted jet washing influence on the juvenile seedling. It showed that the percent of zygotes released was increased with time in the first 60 hrs. The capacity of germlings attached to the substratum was significantly increased, especially coincident with the time of the new rhizoids emerged and elongated. The detachment rate of germlings significantly decreased with the delay of starting time of jet washing or the reduction of jet washing velocity. However, the jet washing at any level applied in the experiment could cause considerable loss of germlings within the 20 days after the attachment.We investigated the variations about leaf length of germlings, leaf width of germlings, leaf number of germlings, and germling density on collector during the early culture at sea. Results showed that the germlings cultured at the lower depth(0-10 cm depth) were significantly better than that at other depth(40-50 cm, 80-90 cm). The germling detachment was all found at different depth groups and germling detachment rate was not significantly influenced by depth.Five populations of S. thunbergii which were respectively collected from Dalian, Weihai, Qingdao, Wenzhou, and Fuzhou were analyzed for a better understanding about the genetic diversity of the species along Chinese coast. Random amplified polymorphism of DNA(RAPD) analysis was conducted in these populations. Twenty one out of 60 polymorphic 10-base random primers were selected, by which 207 useful loci were detected. The polymorphic loci, Nei’s gene diversity and Shannon diversity index were: 89.5%, 0.2966, 0.4508, respectively. The coefficient of genetic differentiation was 0.6131 and the gene flow(Nm) was 0.3155. The results of AMOVA showed significantly genetic differentiation among populations. High level of genetic differentiation among different populations and low level of genetic diversity of S. thunbergii were revealed.