Harmful algal bloom-forming dinofl agellate Prorocentrum donghaiense inhibits the growth and photosynthesis of seaweed Sargassum fusiformis embryos

Harmful algal bloom(HAB)is an ecological disaster to local mariculture.At present,its impact on macrophytes has not been well studied.In this study,we cultivated sexually propagated embryos of S argassum fusiformis-an edible seaweed-in Prorocentrum donghaiense suspensions at different cell densities(0,0.50×10^(5),0.75×10^(5),1.00×10^(5),and 1.50×10^(5) cells/mL)for 10 days,during which growth and photosynthetic activities of the embryos were determined,and a monocultivation was set up for comparison.Results show that the relative growth rate and photosynthetic activities of the embryos co-cultivated with P.donghaiense were inhibited mostly and significantly in the cell densities of 0.75×10^(5),1.00×10^(5),and 1.50×10^(5) cells/mL,and the inhibitory effects increased in overall with increased cell densities.The maximum relative electron transport rates(rETR max)and apparent photosynthetic efficiency(a)of co-cultivated embryos were all significantly lower than monocultivation ones on the 10 th day.Furthermore,the photosynthetic activity detected by chlorophyll-a fluorescence transient(i.e.,OJIP),the electron transport among electron transfer accepters of PSII(photosystem II)and that from PSII to PSI(photosystem I)was restricted,which is probably responsible for the decreases of rETR max andain the co-cultivated embryos.In addition,parts of the photosynthetic reaction centers of PSII in the co-cultivated embryos were inactivated.Therefore,P.donghaiense bloom could restrain the development and photosynthetic activities of S.fusiformis embryos,reduce the seedlings stock,and eventually hinder the development of S.fusiformis production industry.

Competitiveness of alga Microcystis aeruginosa co-cultivated with cyanobacterium Raphidiopsis raciborskii confirms its dominating position

Microcystis aeruginosa has always been regarded as the main culprit of cyanobacterial blooms in freshwater.However,in recent years,Raphidiopsis raciborskii has gradually replaced M.aeruginosa as the culprit of cyanobacterial blooms in some tropical and subtropical shallow lakes.To reveal which one plays a more dominant role,interactions between cylindrospermospin(CYN)-producing R.raciborskii and microcystins(MCs)-producing or non-MCs-producing M.aeruginosa strains were studied using bialgal cultures at different initial ratios of biomasses of the two species at 25℃.During the co-cultivation,the M.aeruginosa strains inhibited the growth and heterocyst formation of R.raciborskii filaments,and thus occupied a dominant position during the co-cultivation regardless of the initial biomass ratios in the cultures.In addition,the MCs-producing M aeruginosa strain contributed to a higher portion of the total biomass and exerted a stronger inhibitory effect on R.raciborskii compared with the non-MCs-producing strain.However,the growth of both MCs-producing and non-MCs-producing M.aeruginosa strains was stimulated by R.raciborskii in the co-cultures compared with M.aeruginosa monoculture,indicating that M.aeruginosa could outcompete R.raciborskii if given enough time,enabling it to develop into the dominant species even in very low initial concentration.To our best knowledge,this is the first report on the loss of heterocyst formation by a species of cyanobacteria that resulted from interactions between two different species of cyanobacteria.These findings indicate that it is difficult for R.raciborskii to replace the dominant position of M.aeruginosa under the experimental environmental condition,and the allelopathic effects of M.aeruginosa on R.raciborskii could significantly contribute to the success of M.aeruginosa.

Tidal water exchanges can shape the phytoplankton community structure and reduce the risk of harmful cyanobacterial blooms in a semi-closed lake

For estuaries,inland lakes play a vital role in the ecological balance under the impact of tide s.The effect of tides-induced water exchange on phytoplankton community in a semi-closed lake was studied and compared with that of an adjacent closed lake in the Oujiang River mouth in Zhejiang,East China Sea,from June 29,2020 to June 14,2021.Results show that the dominant species,abundance,dominance,and diversity of the phytoplankton species between the two lakes were significantly different.In the closed lake,cyanobacteria were the dominant species during the study period.However.in the semi-closed lake,the diversification of the dominant species was greater,and some species of diatoms and green algae became dominant.The average phytoplankton abundance in the closed lake was 6 times of that in the semi-closed lake.The average dominance of cyanobacteria in the closed lake was 0.96,and those in the semi-closed lake and the Oujiang River were 0.51 and 0.22,respectively.Cyanobacterial blooms occurred throughout the study time in the closed lake but not in the semi-closed one.Furthermore,the species diversity richness of the phytoplankton in the semi-closed lake was higher than that of the closed one,and the phytoplankton community between the closed lake and semi-closed lake could be divided into distinctly different groups based on non-metic multidimensional scaling analysis(NMDS)and analysis of similarities(ANOSIM)analysis.The salinity of the water was significantly greater and the transparency significantly smaller in the semi-closed lake than those in the closed lake.Therefore,water exchange driven by local tidal movement increased salinity and decreased transparency of water,which consequently shaped the community structures of different phytoplankton and reduced the risk of a cyanobacterial bloom outbreak in the semi-closed lake.

Oxidative stress responses to cadmium in the seedlings of a commercial seaweed Sargassum fusiforme

Cadmium(Cd)is a common heavy metal pollutant in the aquatic environment,generally toxic to plant growth and leading to growth inhibition and biomass reduction.To study the oxidation resistance in Sargassum fusiforme seedlings in response to inorganic Cd stress,we cultured the seedlings under two different Cd levels:natural seawater and high Cd stress.High Cd stress significantly inhibited the seedlings growth,and darkened the thalli color.Additionally,the pigment contents,growth rate,peroxidase(POD)activity,dehydroascorbic acid(DHA)content,and glutathione reductase(GR)activity in S.fusiforme were significantly reduced by high Cd treatment.Contrarily,the Cd accumulation,Cd2+absorption rate,dark respiration/net photosynthetic rate(Rd/Pn),ascorbic acid(Vc)content,soluble protein(SP)content,glutathione(GSH),and the activities of superoxide dismutase(SOD)and catalase(CAT)of S.fusiforme under Cd treatment significantly increased compared to the control group.The decrease of malondialdehyde(MDA)was not significant.Although S.fusiforme seedlings increased the antioxidant activities of POD,SOD,Vc,and the AsA-GSH cycle to disseminate H2O2 and maintain healthy metabolism,high Cd stress caused Cd accumulation in the stem and leaves of S.fusiforme seedlings.The excessive Cd significantly restricted photosynthesis and reduced photosynthetic pigments in the seedlings,resulting in growth inhibition and deep morphological color,especially of the stems.High levels of Cd in seawater had toxic effects on commercial S.fusiforme seedlings,and risked this edible seaweed for human food.

Integrated microalgae culture with food processing waste for wastewater remediation and enhanced biomass productivity

Waste generation from food manufacturing facilities poses a serious hazard like environmental degradation, water pollution, and land pollution due to its high nutrient composition. Specifically, solid waste(powder) disposal requires additional energy sources in terms of scientific treatment, structured collection, and disposal packaging according to the safety regulation. Thus, this research discusses the viewpoint of integrating food processing waste as an organic carbon source with BG-11 medium for Chlorella vulgaris(FSP-E) growth. The food processing waste powders investigated in this study were obtained from milk, and biscuit manufacturing facilities. The culture medium was modified by combining both BG-11 and food processing waste powders to identify the optimal algal growth and biochemical content.Compared to the microalgae grown in BG-11 alone(IBG), the combination of biscuit waste and IBG produced higher biomass concentration(44%), with increased lipid(11%), protein(20%), and carbohydrate(57%) contents. Chlorella vulgaris was able to uptake nutrients from the culture medium with combination of food processing waste and IBG thus enhancing its growth. The results obtained also indicate that an integrated culture system using food processing waste and synthetic sources can generate energy out of waste by improving the bio-composition of the microalgae biomass.