Molecular phylogenetic analyses of Ulva (Chlorophyta, Ulvophyceae) mats in the Xiangshan Bay of China using high-resolution DNA markers

Intertidal Ulva mats occur annually in winter and spring in the Xiangshan Bay (29°26′–29°34′ N, 121°27′–121°50′ E) of China. Thousands of tons of Ulva biomass have been harvested as edible seaweeds for human consumption for several decades in this region. This investigation was designed to quantify Ulva microscopic propagules associated with the mat, identify species composition, and to analyze intra-species relationships using three molecular markers. Phylogenetic analysis based on the nuclear encoded rDNA internal transcribed spacer region, the plastid encoded large subunit of the ribulose 1,5-bisphosphate carboxylase gene, and the 5S rDNA spacer region showed that the mat was principally composed of Ulva prolifera and Ulva flexuosa. Their propagules were detected in both the water column and sediment. Based on phylogenetic analyses of the 5S rDNA spacer region, mat samples of U. prolifera and U. flexuosa were genetically distinct from the green tide samples in the Yellow Sea and U. flexuosa samples from Jiangsu coasts, respectively, revealing that isolated geographical position of the Xiangshan Bay might result in the maintenance of a distinct Ulva population. The results demonstrate that high-resolution DNA markers have great potential in identification and discrimination at and below the species level.