A Taxonomic Revision Of The Genus Sargassum(Fucales,Phaeophyceae) In The The Yellow Sea And The East China Sea

Sargassum C.Agardh is the most diverse genus in Phaeophyceae,and particularly abundant in tropical and subtropical regions and the Indo-Pacific.These morphological criteria used by traditional classification system can be highly variable due to environmental conditions or the developmental stage of the thallus.It is very hard to identify species only based on the morphological variability.Foreign phycologists have been carried out molecular markers revision of Sargassum and proposed a few taxonomic synonymies recently.The species diversity of the genus in the China Seas has not yet been revaluated based on integrative molecular evidence.Therefore,in the present proposal,we will carry out a taxonomic revision on Sargassum using the specimens in the filed survey recently and those deposited in the Marine Biological Museum of the Chinese Academy of Science(MBMCAS),with a combination of morphological and phylogenetic analyses.The main aim of this study is to correct the incongruities of traditional classification and reassess the status of specie and to clarify the distribution of Sargassum in the Yellow Sea and the East China Sea.Based on the morphological comparison of type specimens and the original diagnosis,in the subgenus Bactrophycus,we confirmed the presence of at least seven species occurring in the Yellow Sea and the East China Sea,including: Sargassum confusum,S.fusiforme,S.hemiphyllum var.chinense,S.horneri,S.muticum,S.siliquastrum,and S.thunbergii.As to S.subgen.Sargassum,only one morphological taxon spanning arrange of morphological continuum were recognized,which made it difficult to assign a species name as three previously described species: S.shandongense Tseng,C.F.Zhang et Lu,S.qingdaoense Tseng et Lu,and S.vachellianum Greville.Furthermore,the nuclear internal transcribed spacer 2(ITS-2),mitochondrial cytochrome oxidase subunit ?(cox3)and the large subunit gene of chloroplast ribulose 1,5-diphosphate ribulose carboxylase(rbc L)were used to assess the taxonomic relationships and classification of Sargassum in the Yellow Sea and the East China Sea.The results indicated that the sequences were nearly identical among three species of S.shandongense,S.qingdaoense and S.vachellianum.Therefore,we proposed that S.shandongense and S.qingdaoense were taxonomic synonyms of S.vachellianum.It also should be considered that the previously decribed S.shandongense and S.qingdaoense are the geographical populations of S.vachellianum,and the subtle morphological variations among populations detected probably resulted from different environmental conditions.In addition,the result of molecular phylogenetic analysis combing the specimens collected from the South China Sea and Japan suggested that S.piluliferum in the subgenus Phyllotrichia should be in the Section Sargassum(belonging to subgenus Sargassum),and S.mcclurei and S.emarginatum in the subgenus Bactrophycus should be in the Section Ilicifolia.In the study,we found that the distribution area of Sargassum in the Yellow Sea and the East China Sea was significantly shrunk,and several species previously recorded in the Yellow Sea and the East China Sea might be disappeared,including: Sargassum capitatum,S.fulvellum,S.graminifolium,S.nigrifolioides,S.patens,S.ringgoldianum and S.serratifolium.It suggests that human activities may be the main reason for the drop in the biomass of Sargassum and the decrease of diversity.