Physiological Ecology And Invasion Risk Of Alexandrium Insuetum From Ballast Water Sediments

Ballast water sediments is the main carrier of transport and transfer of dinoflagellate cysts.In recent years,invasion of alien dinoflagellate species caused by ballast water sediments has been widespread.To explore the invasion risk of dinoflagellate cysts in the ballast water sediments of foreign ships,species of living dinoflagellate cysts in the ballast water sediments of five foreign ships in Jiangyin Port were identified and analyzed.The cysts of non-indigenous marine dinoflagellate species on Chinese coasts were selected and germinated.The potential invasion risk of suspected invasive species was explored and evaluated through physiological ecology experiments and competitive experiments.The main results showed that:1)Twenty-nine species of dinoflagellate cysts belonging to nine genera,including gonyaulacoids,calcoidinellids,gymnodinioids,diplopsalids and protoperidinioids,were identified on the ballast water sediments of five foreign ships in Jiangyin port.The density of living cysts was 1 to 45 cysts/g dry weight.The community structure of dinoflagellate cysts in ballast water sediments of different ships were different,but all ships contained toxic and/or harmful dinoflagellate cysts.2)An unrecorded dinoflagellate cyst type on Chinese coasts which was identified as Alexandrium insuetum(strain RCME-2)were found on the basis of its morphological characteristics and molecular biology information.The cysts of RCME-2 were nearly spherical,and the vegetative cells were pear-shaped.The surface of shell plate distributed a dense network structure.Phylogenetic analysis showed that RCME-2 was most similar to the A.insuetum strains of Japan and Korea.3)Physiological and ecological experiments showed that the Alexandrium insuetum(strain RCME-2)could grow and reproduce in environment with temperature of 15-30? and salinity of 20-35.At the temperature of 20? and the salinity of 35,the species had a maximum cell density of 1.94×104 cells/m L and a maximum specific growth rate of 0.240 d-1.Moreover,A.insuetum could effectively use a variety of common nitrogen sources and phosphorus sources;it grew best in environments with Na NO3 as the nitrogen source and glycerolphosphate as the phosphorus source.4)Alexandrium insuetum had a competitive advantage in co-culture experiments with Prorocentrum donghaiense and Alexandrium tamarense.In these experiments,the biomass of P.donghaiense decreased rapidly during the co-culture process and disappeared on the 6th day.Filtrate culture experiment showed that the cell-free filtrate of A.insuetum can inhibit the growth of P.donghaiensis: the biomass of P.donghaiense could be reduced by 62% by applying 100% filtrate.5)Scanning for the presence of 57 hydrophilic toxin components and 22 lipophilic toxin components in the extract of Alexandrium insuetum was carried out by liquid chromatography tandem quadrupole mass spectrometry(LC-MS/MS)analysis.The results showed A.insuetum did not produce any hydrophilic and lipophilic toxins.But its chloroform and methanol extracts showed high hemolytic added up to 122.46 HU/L or equivalently 1.36×10-5 HU/cell,which was much higher than that of other algae.The competitive advantage of A.insuetum over other algae probably comes from some hemolytic substances secreted by cells.6)By applying the experimental results and information from the literature to the hierarchical index system of marine biological invasion risk assessment,we determined that A.insuetum is a high-risk marine invasive dinoflagellate.