The current situations of green macroalgae and micro-propagules in Pyropia aquaculture of the Subei Shoal in spring of 2013

To discover the distribution of green algal micro-propagules in the Subei Shoal and clarify the growth of green macroalgae attached on Pyropia aquaculture rafts,an integrated investigation in Pyropia aquaculture area and one cruise in the coastal area of the Subei Shoal were carried out from March to May in 2013.The results showed that green algal micro-propagules were discovered in seawater and sediment during March to May.The average quantity of micro-propagules was 267 ind./L in surface seawater and 43 ind./g in sediment.The biomass of attached green macroalgae increased in Pyropia aquaculture from March to May.Three species,including Ulva prolifera,Ulva linza and Blidingia sp.were found in Pyropia aquaculture rafts.The dominant specie was Blidingia sp.and the second was U.prolifera in spring.This study indicated that the micro-propagules and macroalgae were existed in the coastal area of the Subei Shoal at the early stage of green tide.This was the key point to the governance of green tide in China.

Unprecedent green macroalgae bloom:mechanism and implication to disaster prediction and prevention

Green macroalgae bloom(GMB),with the dominant species of Ulva prolifera,has regularly occurred since 2007 along the China coast.Although disaster prevention and control achieved favorable results in 2020,the satellite-observed GMB annual maximum coverage(AMC)rebounded sharply in 2021 to an unprecedented level.The reasons for this rebound and the significant interannual variability over past 15 years are still open questions.Here,by using long-term time-series(2007-2022)optical and Synthetic Aperture Radar satellite observations(1000+scenes),meteorological data and water quality statistics,the mechanism analysis was performed by exploring effects from natural factors and human activities.Two key determinants for AMC are successfully identified from numerous potential factors which are the macroalgae distribution in a key area(the Subei Shoal)during a critical period(from April to May 20)and the nutrient availability.Furthermore,by using these two parameters,a novel model for AMC prediction(R^(2)=0.87,p<0.01)is proposed and independently validated,which can reasonably explain the significant interannual variability(2014-2021)and agree well with the latest observation in 2022(percentage difference 12%).Finally,suggestions are proposed for future disaster prevention and alleviation.This work may aid future bloom prediction and management measure optimization.

Allelopathic growth inhibition of Heterosigma akashiwo by the three Ulva spcieces(Ulva Pertusa,Ulva Linza,Enteromorpha intestinalis) under laboratory conditions

Allelopathic effects of several concentrations of fresh tissue,dry powder and dry tissue of three bloom-forming green macroalgae Ulva pertusa,Ulva linza and Enteromopha intestinalis on the red tide microalga Heterosigma akashiwo were evaluated in microcosms systems.The effects of macroalgae culture medium filtrate were investigated on H.akashiwo using initial or semi-continuous filtrate addition.Preliminary studies on the algicidal effects of one aqueous and four organic solvent extracts from the macroalgae on the microalga were carried out to confirm the existence of allelochemicals in the tissue of these macroalgae.The dry powder of U.pertusa was extracted with methanol,and the methanol extracts were partitioned to petroleum ether phase,ethyl acetate phase,butanol phase and distilled phase by liquid-liquid fractionation.The bioassays of the activity of every fraction were carried out on H.akashiwo.The resultant microcosms assay showed that the growth of H.akashiwo was strongly inhibited by using fresh tissues,dry powder or dry tissue of these three macroalgae,while aqueous and methanol extracts of both macroalgae had strong inhibitory effects on the growth of H.akashiwo,and the EC50 values for methanol extract of U.pertusa,U.linza or E.intestinalis were 0.016,0.028× 10-12 or 0.033× 10-12,respectively.While the other three organic solvent extracts (acetone,ether and chloroform) had no apparent effect on its growth,this suggests that the allelochemicals from these three maeroalgae had relatively high polarities.The activity of petroleum ether phase,ethyl acetate phase,butanol phase and distilled phase of U.pertusa methanol extract was carried out on H.akashiwo indicating that petroleum ether phase and ethyl acetate phase had stronger algicidal effect on H.akashiwo.The inhibition effect of the ethyl acetate phase was not as strong as that of petroleum ether phase,and effective concentration of petroleum ether phase was 17 mg/L for H.akashiwo.However,no significant algicidal effects were observed on the butanol phase and distilled water phase.These three macroalgae's culture medium filtrate exhibited no apparent growth inhibitory effect on the microalga under initial filtrate addition whereas the growth of H.akashiwo was significantly inhibited under semi-continuous filtrate addition,which suggests that continuous release of small quantities of rapidly degradable allelochemicals from the fresh tissue of both macroalgae was effective in inhibiting the growth of H.akashiwo.