Investigation On Potential Toxic And Harmful Phytoplankton In Weizhou Island

Phytoplankton is a kind of micro plant widely distributed in the water on the earth,which has the characteristics of small size,short life cycle and many species.As one of the most important primary producers in marine ecosystem,phytoplankton is closely related to marine fishery resources.When its explosive proliferation or high aggregation reaches a certain density,it will cause red tide.The occurrence of red tide will destroy the marine ecosystem,affect the sustainable development of the ocean,and cause economic losses to the aquaculture industry,even harm for human health.Weizhou Island is the largest island in the Beibu Gulf of Guangxi,with a total area of24.98km~2,latitude and longitude of 20°54'-21°10'N,109°00-109°15'E,belonging to subtropical monsoon climate.Because of its unique geographical environment,superior marine environment and folk customs,Weizhou Island has a very high value in tourism.Weizhou Island is a hot area for the occurrence of red tide in Beibu Gulf,in the past 30 years,red tide often occurs in Weizhou Island.From 2001 to 2010,70%of the red tide in Beibu Gulf occurred in Weizhou Island.Therefore,understanding the potential toxic and harmful phytoplankton in the waters of Weizhou Island in Beibu Gulf can provide scientific data for the utilization of marine biological resources,marine environmental protection,early warning and effective control of red tide in Weizhou Island.Eight sampling points were set around Weizhou Island,and phytoplankton samples were collected in September(Autumn),December(winter)of 2018 and March(spring),June(summer)of 2019,respectively,to analyze the environmental factors of sampling waters.The samples were separated and purified by capillary separation under the laboratory light microscope,and the culture was expanded step by step.The morphological characteristics of target algae were analyzed by optical microscope,and the identification of genus level was basically completed.Then,the sequence of small subunit ribosome RNA gene(SSU r DNA)and large subunit ribosome RNA gene(LSU r DNA)and internal transcribed spacer(ITS)were sequenced.The obtained sequence was checked manually by MEGA 7.0 software and analyzed by base statistics.Genetic distance was calculated and analyzed based on Kimura 2-parameter,and phylogenetic tree was constructed by maximum likelihood method.The results show that the sampling sea area quality of Weizhou Island is good,and the sea water and sediment basically meet the national first-class standard.In this study,51 strains of potentially toxic harmful algae and algae were constructed,including 11 species from 6 genus and 4 phyla.It was found that::1)11 species of potentially toxic phytoplankton,including:Alexandrium affine,A.tamiyavanichii,A.pseudogonyaulax,Prorocentrum koreanum,P.sigmoides,P.triestinum,P.rhathymum,Skeletonema tropicum,Akashiwo sanguinea,Phaeocystis globosa,Chattonella marina.Among them,Phaeocystis globosa and Prorocentrum koreanum distributed in the whole island,and Phaeocystis globosa mainly occured in spring,Prorocentrum koreanum has been found in four seasons.2)Except for Alexandrium affine,A.pseudogonyaulax,P.koreanum,Prorocentrum triestinum and Phaeocystis globosa,which have been identified by previous researchers and have molecular taxonomic data,the other 6 species have obtained taxonomic gene data for the first time in the Beibu Gulf region,and A.tamiyavanichii,P.rhathymum,all of the 2 species are reported in Beibu Gulf for the first time.3)Among the 11 potential toxic microalgae found,6 are potential toxic phytoplankton,including:Alexandrium affine,A.tamiyavanichii,A.pseudogonyaulax,Prorocentrum rhathymum,Phaeocystis globosa,Chattonella marina/C.marina var.marina/C.marina var.antiqua/C.marina var.ovata.This study is the first time to build algal culture collection of potential toxic and harmful phytoplankton in Weizhou Island,and to classify the species and structure of potential toxic and harmful phytoplankton in Weizhou Island.The results will provide the provenance and biological basis for the study of marine biotoxin,the safety of marine products consumption and trade,the protection of marine environment and the utilization of marine resources in Weizhou Island and Beibu Gulf.