The Species Composition And Distribution Of The Attached Ulva Spp.along The Coast Of The Yellow Sea,China

Under the dual influence of global warming and human activities,green tides caused by the green algae Ulva is obviously on the rise around the world,especially in the coastal areas of China.In the Yellow Sea of China,green tides dominated by Ulva prolifera has become a regular marine disaster,which has a significant impact on the coastal ecosystem.To efficiently monitor and forecast green tides,it is first necessary to determine the composition and distribution characteristics of the attached Ulva species in relevant waters.Previous studies have shown that the Yellow Sea green tide is caused by a unique floating ecotype,which has distinct genetic differences with all attached populations that are widely collected from the coastal areas of China.Every year,a large number of floating green algae hit the coast of the Yellow Sea,releasing abundant germ cells.However,there is still a lack of comprehensive understanding that if the species composition of the attached Ulva has changed and in turn provide new provenance for the blooms.In China,seaweed diversity,including Ulvaspecies,has been investigated mainly based on morphological features,while there are a few characters used for identification and those features could vary widely.In view of these problems,the samples of Ulva species were collected extensively in various habitats along the coast of Yellow Sea and identified by multiple molecular markers.Based on bioinformatics method,combined with the years of our research on Ulva along the coast of China and all the sequence information that are available in NCBI,the distribution characteristics of all new records were analyzed and summarized,as well as the possible dispersal patterns.Morphological observation and description of some important green-tide-forming species were performed.The main results are as follows:1)A total of 380 Ulva samples were collected from 29 representative sites and 15 Ulva species were identified by molecular identification,including 9 known species of the Yellow Sea:U.prolifera,U.linza,U.compressa,U.intestinalis,U.aragoensis,U.flexuosa,U.rigida,U.australis and U.torta.By comparing with historical data,it was found that the cold temperate species U.intestinalis has shifted northward in some extent.2)Using the molecular marker SCAR specific to the Yellow Sea green tide floating ecotype,91 samples isolated from 10 attached Ulva populations were analyzed and the results showed that only one individual was positive,indicating that the floating ecotype U.prolifera has not established in large numbers along the coast yet.3)In addition,based on bioinformatics method,combined with the years of our research on Ulva along the Chinese coast and highly similar sequences in GenBank,six Ulva sp.were respectively identified as U.meridionalis,U.tepida,U.chaugulii,U.simplex,U.partita and U.splitiana,which were all new records in China.Then the distribution characteristics of these six Ulva species in China and around the world were analyzed,suggesting that U.meridionalis,U.chaugulii,U.partita and U.splitiana may be new invaders.Furthermore,it has been found that the subtropical species U.meridionalis,U.tepida and U.chaugulii had caused green tides in the South China Sea,and U.meridionalis had spread significantly northward to the temperate zone.4)As for the green-tide-forming species U.meridionalis,the morphological characteristic,individual development and reproduction were observed in detail.The results showed that the morphogenetic pattern of Ulva meridionalis is significantly different from the three known ones of Ulva species.This research preliminarily revealed the composition and distribution characteristics of the attached Ulva species along the coast of the Yellow Sea,China,confirmed that the shore-based Ulva prolifera made no contribution to the Yellow Sea green tide,and indicated that the new green tide could be induced by bioinvasion.These research results will provide important background data and scientific basis for early monitoring,ecological effect assessment and evolution trend prediction of green tides in Chinese coast.