Population Growth Dynamics And Cyst Formation Mechanisms Of Akashiwo Sanguinea

Harmful algal blooms are frequently observed in coastal waters, which threatenthe coastal ecological environment and public health. Lots of factors contributed tothe formation of HABs, such as environmental (e.g. temperature, salinity, irradiance)and chemical (nutrients), which attract much attention from researchers. Akashiwosanguinea is a typical causative species of HABs in coastal waters of China. Therehad been various works regarding meteorological, biological, and chemical aspectsduring red tides, however, limited studies had been conducted on population growthdynamics and cyst formation of A.sanguinea, which are necessary needed to for betterunderstanding of the blooms dynamics of A.sanguinea.A.sanguinea, the major causative species of the red tide in Sishili Bay, Yantai,Shandong, is selected as the target species in this study. Our main odjectives were tostudy the growth dynamics of A.sanguinea when exposed to different environmentand nutrient conditions in controlled laboratory settings. The preliminary studies ofcyst formation mechanisms under nutrient limitation conditions were alsoinvestigated. The results are as follows:(1) A.sanguinea could acclimate to a broad range of temperature, salinity andirradiance variation. A.sanguinea had optimal growth within the temperature range of20~25℃, salinity of20and illumination of4000lx. But when temperature drops to15℃or rises up to30℃, salinity rises up to40, A.sanguinea grows slowly, and theexpansion ability decreases. Orthogonal experiment shows that A.sanguinea achievesfaster growth at temperature and salinity with the optimum range, while salinity andtemperature unilaterally raise or drop are not suitable for its rapid proliferation.(2) A.sanguinea could utilize different kinds of dissolved inorganic nitrogensubstrates, for example, nitrate and ammonium. Within the experimental range （10~200μM）, the biomass and the NO3-concentrations are positively correlated.Low concentrations of NH4+(10~100μM) promote the growth of A.sanguinea, whilehigh concentrations produce significant toxic effect and inhibit its growth.A.sanguinea tends to prefer NO3-as compared to NH4+.(3) Various types of dissolved organic nitrogen substrates can be utilized byA.sanguinea, including urea, peptone and amino acid. The maximum specific growthrate of A.sanguinea is0.31d-1when urea nitrate (100μM) as its sole nitrogen source,followed as his and peptone (1.17~0.18d-1). Among the four kinds of amino acid,nitrogen uptake of A.sanguinea exhibits obviously variation, and A.sanguinea growsbetter with addition of amino acid nitrogen.(4) Cysts formation is observed when cultured in N-limitation conditions, and isa biological response to the stressful environmental conditions of nutrient depletion.The size and shape of cysts are different from vegetative cells. Cysts are observed atthe second day after inoculation under N limitation conditions. The ratios ofencystment are similar among the tested groups, ranging from8.77%to22.25%. Themaximum number of cysts are291,158cells/mL when cultured in nitrate orammoniumlimitation condition.