Morphological characteristics and molecular phylogenetic analysis of green tide Enteromorpha sp. occurred in the Yellow Sea

Green tide is one of the major environmental problems over the world. Ulva and Enteromorpha are two of the best known marine green alga genera,which widely distribute in marine,freshwater and brackish environments throughout the world and are responsible for widespread green tides. Approximately 80 species are now included in Enteromorpha genera,of which only 11 species are currently recognized in China. A large-scale green tide occurred in the middle and south area of Yellow Sea in June,2008. The green tide algae were classifi ed as Enteromorpha genera from their morphological characteristics,but their taxonomy at species level was uncertain and became the most controversial issue. In this study,molecular data were used in parallel with morphological characters to resolve the taxonomic problems. Twenty-two samples from Yellow Sea and one free- floating sample from Zhanqiao of Qingdao have been studied. The segment selected for molecular phylogenetic analysis were internal transcribed spacers (ITS1 and ITS2) and 5.8S rDNA gene. The results show that all samples have typical morphological characters of Enteromorpha,such as distinct thalli and branches. And the section view showed that all samples form hollow tubes of one cell thick,and the cells particularly locate in the middle of the tube. But they are different in thallus length and width,cell size and colour which are from dark green to light green,and to yellow-green. Molecular phylogenetic analysis was used to test whether they belong to the same species. All the 23 ITS and 5.8S rDNA sequences are identical and they clustered in the same clade with Enteromorpha prolifera in the phylogenetic tree based on the sequences of ITS and 5.8S rDNA,indicating that they belong to the same species of Enteromorpha prolifera.