Green algae blooms caused by Ulva prolifera in the southern Yellow Sea: Identification of the original bloom location and evaluation of biological processes occurring during the early northward floating period

Over the past 6 yr, green algae blooms mainly caused by Ulva prolifera have been recorded in the Yellow Sea. Although satellite images provide a clear picture of the formation of these macroalgal blooms, the location of the original bloom area and the biological processes that occur during the early northward floating period remain poorly understood. Results obtained from more than 50 cruises conducted along coastal areas of the southwest Yellow Sea showed that the blooms originated along the coast of the Rudong area, where oceanographic conditions were favorable for accumulation of floating green algae. The dominant Ulva species changed during the period of northward drift. Massive floating Ulva blooms dominated by U. prolifera occurred mainly from June until the bloom disappeared. U. prolifera dominated the assemblage due to its rapid growth and production under suitable environmental conditions and its apparent competitive advantages over other Ulva species. Phylogenetic analysis of 5S spacer sequences showed that U. prolifera blooms in the Yellow Sea were not from a single genetic source and likely originated from or were supplemented with a number of different genetic sources.