Genetic Diversity Of Ulva Prolifera Population Within Qingdao’s Green Bloom Revealed By Microsatellite

The large-scale green tides have occurred in Qingdao coast in China for seven consecutive years from 2007 to 2013. Especially in the summer of 2008, the world‘s largest green tide bloom occurred in the coast of Qingdao, which caused serious social problems as well as marine ecological issues. It is essential to study the species composition, genetic structure and genetic diversity of these green tides for understanding the green blooms and finding possible solutions to the problems.To provide more information on the species composition of these green tides and explore the genetic structure of Ulva prolifera bloom in 2013, 210 free-floating samples isolated from green algae bloom in Qingdao coast in June 19, 2013 were identified based on the ITS, rbc L and 5S sequence. Additionally, some microsatellite primers were developed from ISSR primers and in terms of the expressed sequenced tags(EST) from Gen Bank, and the genetic diversity was investigated using them.According to the ITS sequence and rbc L gene, 210 samples from green tide in Qingdao were grouped to one clade with U. linza-procera-prolifera(LPP) complex. To confirm the taxonomic status of the LPP complex, all samples were further analyzed based on 5S sequences. According to 5S sequence, all samples from Qingdao sea area during the green algae bloom were attributed to U. prolifera clade. These data indicate that green tide in Qingdao, at least in 2013, may be dominated by a single species, U. prolifera.Total eight microsatellite primers were developed on the basis of EST sequences and ISSR primers. The 8 microsatellite markers provided a total of 17 alleles, exhibiting 1~3 alleles at each locus with an average of 2.125. The number of effective alleles ranged from 1.000~1.235 with an average of 1.160. The Nei‘s genetic diversity ranged from 0.000~0.189 with an average of 0.064, whereas Shannon index ranged from 0.00~0.367 with an average of 0.133. These data suggest that the genetic diversity of U. prolifera population within Qingdao’s green bloom is very low. The life history and pathways of reproduction of U. prolifera are known to be multifarious including sexual, asexual and vegetative propagations. Among them, asexual pathway may be the most important mode of reproduction in U. prolifera. Therefore, we proposed that the pathways of reproduction of U. prolifera and the high degree of adaptability to environment may be responsible for the lower diversity of floating U. prolifera. However, it is note of that the microsatellite primers used in this study were from EST sequences or developed from the ISSR primers due to the unavailable genomic sequence of U. prolifera, which might decrease the polymorphism of these primers to some extents. Therefore, further study should be addressed before drawing any conclusions about the genetic diversity of U. prolifera population within Qingdao’s green bloom with more molecular markers.