Molecular detection and analysis of green seaweeds from Rudong coasts in Jiangsu Province

Since 2007, massive green tides have occurred every year in the Yellow Sea in areas such as Qingdao, Lianyungang and Rudong. In 2008, Qingdao experienced the largest Ulva bloom in the world, which caused an ecological disaster. In 2009, survey and monitoring of green seaweeds was conducted in the Rudong sea area of Jiangsu Province. We sequenced and analyzed the nuclear encoded internal transcribed spacer (ITS) and associated 5.8S rDNA regions as well as the chloroplast rbcL genes for 11 attached samples and 15 free-floating samples of green algae collected from Rudong coasts. The investigation showed that a large amount of sessile Ulva existed in Rudong coastal areas. In addition, the floating green algae clusters appeared earliest in Rudong, and gradually drifted northwards. The phylogenetic analysis of ITS sequences revealed that the samples fell into five distinct clades: the Ulva compressa clade (6 samples), the Ulva linza-procera-prolifera (LPP) complex clade (12 samples), the Ulva flexuosa clade (3 samples), the Blidingia sp. clade (3 samples) and the Urospora spp. clade (2 samples). However, the 26 samples formed just four clades in the phylogenetic tree of rbc L sequences, which indicated the higher conservativeness of rbc L. DNA sequencing analysis implied there were Ulva compressa , Ulva flexuosa and LPP complex in both the free-floating Ulva and the attached species from Rudong coasts and that the final free-floating strain was the same as the dominant Ulva species ( U. prolifera ) of the 2008 bloom in the Yellow Sea. This study laid significant foundations for source-tracing and prevention of Ulva blooms in the Yellow Sea.