Quantitative Distribution Properties Of Ulva Microscopic Propagules In The South Yellow Sea And Source Tracing

Green tide was caused by Ulva prolifera in the Yellow Sea. Since2007, the green tide with large scale has been successively occurred for7years. The influenced area and covering area of green tides increasedevery year, and it has became one of the main marine disasters in theYellow Sea. The origin of green tides bloomed in the Yellow Sea has beenthe controversial focus issues. At present there were a variety of viewsabout the green tide origin. Some believed that floating green algae mightcame from Porphyra aquaculture rafts in coasts of Jiangsu province, andsome believed that floating green algae at coastal seawater ponds play animportant role for the seawater with microscopic propagules came fromcoast, while others believed that there was some seaweed beds at thesouth coast of Yellow Sea, and they might be the origin of green tide. Sountil now，the origin of green tide in Yellow Sea is not very clear, and theprevention and control measures for the green tides could not be targeted.In this paper, the quantitative distribution of Ulva microscopicpropagules in the South Yellow Sea of2012and2013were monitored tofind the green tide origin and evaluate the contribution to the green tideblooming in the Yellow Sea. For searching the green tide origin, thequantitative distribution in aquaculture ponds along coastline of Jiangsu,and the important estuaries, Yangtze river estuary, Porphyra aquaculturerafts area, as well as pelagic zone of south Yellow Sea were investigated.And internal transcribed spacer (ITS) and5S rDNA spacer sequenceswere used to identify the spcecies and analysis the species composition ofUlva microscopic propagules, and evolutionary changes during thegreen tide blooming.1The quantitative distribution and species composition of Ulva microscopic propagules were monitored in the south Yellow SeaThe quantitative distribution of Ulva microscopic propagules in thesouth Yellow Sea in2012-2013were monitored. We found that Ulvamicroscopic propagules widely distributed in the south Yellow Sea, andthe species were Ulva flexuosa, Ulva linza and Ulva prolifera. Thedensity of Ulva microscopic propagules in the offshore area was muchhigher than the pelagic zone of the south Yellow Sea, and the density wasparticularly high in coasts of Rudong and Dafeng in April. The densityreached up to1312ind L–1at Dafeng coast of in April,2012and884indL–1at Rudong coast in April,2013, respectively. The pelagic zone ofYellow Sea are investigated in February, March and May2013, andpropagules density was very low. And there was rare propagule inYangtze River estuary waters, which only be found in February. Itindicated that Ulva microscopic propagules might come from offshorearea of Rudong and Dafeng. In order to determine whether there was alarge natural seaweed bed, the bottom of the south Yellow Sea weremonitored with bottom trawling along Rudong, Dafeng, Sheyang,Binghai sections and voyaged for100km offshore distance. But only afew amount of free-floating Porphyra yezoensis and green tide algae werefound in Rudong and Dafeng. It inticated that there was no seaweed bedin the Rudong, Dafeng, Sheyang, Binghai coasts, and the free-floatingPorphyra yezoensis and green tide algae came from the havesting ofPorphyra growing on the nets of aquaculture rafts.2The green tide algae and their microscopic propagules alongcoastal embankment, aquaculture ponds and important estuaries weremonitored in2013The Ulva green tide algae and its microscopic propagules weremonitored at ten important estuaries and aquaculture ponds alongcoastline of Jiangsu province. The green tide algae and its microscopicpropagules were found in a few estuaries in Qidong and Haimen, thespecies were Ulva flexuosa, Ulva linza and Ulva prolifera. The density ofmicroscopic propagules was very lower than that in offshore area andPorphyra aquaculture area. Also there were few green tide algae in aquaculture ponds. And the aquaculture ponds near south Haozhi portwere monitored with5times, but green tide algae and its microscopicpropagules were found with only3times. The density of microscopicpropagules reached to maximum, about351ind/L in February, thenreduced obviously for several months later. It indicated that the importantestuaries and aquaculture ponds impossibly caused the high densitydistribution of microscopic propagules.3The distribution and composition of microscopic propagules weremonitored in Porphyra aquaculturerafts area, Jiangsu provinceThere were Ulva microscopic propagules with different densities inPorphyra aquaculture rafts area from December2012to April2013. Thespecies of microscopic propagules was mainly composed of Ulvaflexuosa and Ulva prolifera by the analysis of ITS and5S rDNA sequence,and it was similar to the composition of the green tide algae species inoffshore waters. The density of microscopic propagules in Porphyraaquaculture rafts area increased from December2012to April2013. Itwas found that there were two haigher desnsities area in Porphyraaquaculture areas, which had close relationship with the Porphyraaquaculture rafts extensive distribution. And we also found that thedensity of Ulva microscopic propagules in Porphyra aquaculture areaswaas higher than other areas in the south Yellow Sea. It indicated that theUlva microscopic propagules mainly spread from Porphyra aquacultureareas to other areas in south Yellow Sea.From above studies, it indicated that the Porphyra aquaculture raftsin Jiangsu coasts might be origin of green tide in Yellow Sea. But it needsmore further studies in the future.