Ulva diversity in the Yellow Sea during the large‐scale green algal blooms in 2008–2009

In the Yellow Sea of China, large‐scale green tides have broken out for three consecutive years from 2007 to 2009. As part of the efforts to localize the algal source, two cruises were conducted in the early stage and the outbreak stage of the bloom in 2009. We analyzed the morphological and genetic diversity of drifting Ulva specimens and culture‐derived isolates from seawater sampled in different localities. For phylogenetic analyses, the nuclear encoded ribosomal DNA internal transcribed spacer region (ITS nrDNA) and the plastid encoded large subunit of ribulose‐1, 5‐bisphosphate carboxylase/oxgenase gene (rbcL) were used. Our molecular and morphological data indicate that the dominant free‐floating Ulva species in 2008 and 2009 possibly belonged to a single strain of the U. linza‐procera‐prolifera (LPP) clade. The ITS sequences from bloom‐forming algal samples with dense branches were identical to those from U. linza‐like specimens without branches derived from the Yellow Sea. Microscopic individuals of the dominant Ulva strain were detected in eight stations, revealing that spore dispersal in the water helped to enlarge biomass in the water during the outbreak stage of green tide in the Yellow Sea.