Allelopathic interactions between Prorocentrum micans and Skeletonema costatum or Karenia mikimotoi in laboratory cultures

Algal allelopathy is an ecological/physiological phenomenon that has focused attention on the interactions among algae and the production of algal toxins. We investigated the allelopathic interactions between the dinoflagellate genus Prorocentrum micans and diatom genus Skeletonema costatum and between P. micans and dinoflagellate genus Karenia mikimotoi using bi-algal cultures. Because the effects were species-specific and size-dependent, we evaluated the effect of different initial densities. At low densities of P. micans and high densities of S. costatum inoculated into the same medium, the growth of P. micans was weakly restrained, whereas the growth of S. costatum was significantly suppressed. S. costatum and K. mikimotoi were strongly inhibited by P. micans, in both the bi-algal cultures and enriched filtrates. Direct cell-to-cell contact was not necessary to gain a competitive advantage, thus, our results suggest that P. micans inhibited the growth of S. costatum and K. mikimotoi by the release of allelochemical(s). Last, a mathematical model was used to simulate growth and interactions between P. micans and S. costatum and between P. micans and K. mikimotoi in bi-algal cultures.     

Effect of Alexandrium tamarense on three bloom-forming algae

We investigated the allelopathic properties of Alexandrium tamarense (Laboar) Balech on the growth of Prorocentrum donghaiense Lu, Chattonella marina (Subrahmanyan) Hara et Chihara and Heterosigma akashiwo (Hada) Hada in a laboratory experiment. We examined the growth of A. tamarense, C. marina, P. donghaiense and H. Akashiwo in co-cultures and the effect of filtrates from A. tamarense cultures in various growth phases, on the three harmful algal bloom (HAB)-forming algae. In co-cultures with A. tamarense, both C. marina and H. akashiwo were dramatically suppressed at high cell densities; in contrast, the growth of P. donghaiense varied in different inoculative ratios of A. tamarense and P. donghaiense. When the ratio was 1:1 (P. donghaiense: A. tamarense), growth of P. donghaiense was inhibited considerably, while the growth of P. donghaiense was almost the same as that of the control when the ratio was 9:1. The growth difference of P. donghaiense, C. marina and H. akashiwo when co-cultured with A. tamarense indicated that the allelopathic effect may be one of the important factors in algal competition and phytoplankton succession involving A. tamarense. In addition, the filtrate from A. tamarense culture had negative impacts on these three HAB algae, and such inhibition varied with different growth phases of A. tamarense in parallel with reported values of PSP toxin content in Alexandrium cells. This implied that PSP toxin was possibly involved in allelopathy of A. tamarense. However, the rapid decomposition and inactivation of PSP toxin above pH 7 weakened this possibility. Further studies on the allelochemicals responsible for the allelopathy of A. tamarense need to be carried out in future.     

Nutrient compositions of cultured Skeletonema costatum,Chaetoceros curvisetus,and Thalassiosira nordenskildii

We cultured different-sized fractions of dominant phytoplankton species,Skeletonema costatum,Chaetoceros curvisetus,and Thalassiosira nordenski ldii,collected in different sea areas in various seasons,and measured and compared their C,N,P,Si contents.The N content of these species is similar,while the C,P,and Si contents of S.costatum from eutrophic Changjiang (Yangtze River) estuary are higher than those from Jiaozhou Bay (JZB),particularly the content of Si.The C,N,P,and Si contents of cultured phytoplank...     

Growth inhibition and oxidative stress in two species of marine diatoms exposed to 1-phenylethanol

1-phenylethanol(1-PEA)is a flavor extensively used in the production of co smetics,beverages,and food.The release of 1-PEA into coastal environments has aroused great concern.However,its potential effects on marine organisms are still unknown.In order to provide a better understanding of the ecological risks of 1-PEA in marine environments,this study determined the toxic effects of 1-PEA on two marine diatoms(Phaeodactylum tricornutum and Skeletonema costatum).The diatoms were grown in culture medium containing different concentrations of 1-PEA for 96 h.The contents of chlorophyll a,chlorophyll c,glutathione(GSH),malondialdehyde(MDA),and the activities of superoxide dismutase(SOD),catalase(CAT)and glutathione peroxidase(GPx),were measured at the end of the exposure period.1-PEA was shown to significantly inhibit the growth of diatoms,with 96-h EC_(50) values of 257.14 mg/L and 126.46 mg/L in P.tricornutum and S.costatum,respectively.In P.tricornutum,the levels of SOD,CAT,GPx,GSH,and MDA were stimulated only when 1-PEA concentrations were close to or greater than the 96-h EC_(50)value.However,in S.costatum,the activities of SOD and CAT,and the syntheses of two chlorophylls were inhibited even at an exposure concentration below the 96-h EC_(50) value.Taken together,these findings indicate a potential ecological risk by discharging 1-PEA into coastal areas and its species-specific toxic effects on marine organisms.     

COMBINED EFFECTS OF TEMPERATURE, IRRADIANCE AND SALINITY ON GROWTH OF DIATOM SKELETONEMA COSTATUM

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Variation of Bioaccumulation Ability of 2,2’,4,4’- Tetrabromodiphenyl Ether by Marine Diatom Skeletonema costatum Under Different N：P Ratios

The growth, biochemical content and bioaccumulation quantity of 2,2’,4,4’-tetrabromodiphenyl ether （BDE-47） in Skeletonema costatum were studied under different N：P ratios （1, 4, 16, 64 and 128）. All cellular biochemical contents of S. costatum presented decreasing trend over cultivation time. At early stage of cultivation, the cellular protein, carbohydrate and lipid in S. co-statum presented higher values in treatments of N：P=4 and 16. However, they were lower in these treatments at the late stage, but higher in treatments N：P=1 and 128. Similarly, BDE-47 levels per cell of S. costatum were higher in treatments of N：P=4 and 16 at early stage of cultivation, which were 3.8 and 3.7 ng （106 cells）-1, respectively. At the middle stage of cultivation, the BDE-47 level per S. costatum cell lowered;and it further reduced in the treatments of N：P=4 and 16 at the late stage with the values 0.6 and 0.5 ng （106 cells）-1, respectively. However, it rose in N：P=128, reaching up to 2.3 ng （106 cells）-1. Compared with BDE-47 per cell, BDE-47 per algal volume under different N：P ratios did not present obvious difference. The quantity BDE-47 accumulated per cell of S. co-statum was positively correlated with protein, carbohydrate and lipid per cell; meanwhile, the BDE-47 per volume had a positive correlation with biochemical content per volume. The variation of bioaccumulation ability of BDE-47 in S. costatum can be ex-plained by biochemical changes due to N：P ratios.     

Competition Among Dinoflagellate Alexandrium Tamarense, Raphidophyte Heterosigma Carterae and Diatom Skeletonema Costatum under Combinations of Two Temperatures and Five Salinities

INTRODUCTIONFrequentoccurrenceofHAB (HarmfulAlgalBlooms)hasbeenobservedinChinasincethe1 970’s .ThegreatharmtothemarineecosystemandpotentialthreattohumanhealthcausedbyHABhavebecomeamajorconcern .However ,themechanismofHABformationisstillpoorlyunderstood .BothphysicalandchemicalfactorsareconsideredasmaincausesforHABformation ,becauseunderoptimaltemperature ,salinityandnutrientconditions,HABspeciesgrowfastandaremorelikelytoformblooms .Changesintheseenvironmentalfactorsmayleadtoashif…     

Nutrient compositions of cultured Skeletonema costatum, Chaetoceros curvisetus, and Thalassiosira nordenskiöldii

We cultured different-sized fractions of dominant phytoplankton species, Skeletonema costatum, Chaetoceros curvisetus, and Thalassiosira nordenskiöldii, collected in different sea areas in various seasons, and measured and compared their C, N, P, Si contents. The N content of these species is similar, while the C, P, and Si contents of S. costatum from eutrophic Changjiang (Yangtze River) estuary are higher than those from Jiaozhou Bay (JZB), particularly the content of Si. The C, N, P, and Si contents of cultured phytoplankton in JZB increase with size fraction augmentation, and the percentages of C, N, and P follow the same trend, while the percentage of Si remain constant. Moreover, S. costatum from small-sized fraction assimilated Si more easily than C. curvisetus and T. nordenskiöldii, which is explained by the dominance of S. costatum under the conditions of low SiO₃-Si concentration in JZB. The C, N, P, and Si contents of cultured S. costatum collected during summer and winter are higher, which is consistent with the phytoplankton blooming seasons in JZB. The SiO₃-Si concentration of seawater during spring restrain the growth of phytoplankton, supported by the fact that the N, P, and Si contents and their ratios in cells of cultured S. costatum are low in spring season.     

Application of rotifer Brachionus plicatilis in detecting the toxicity of harmful algae

The toxicity of seven major HAB (harmful algal bloom) species/strains, Prorocentrum donghaiense, Phaeocystis globosa, Prorocentrum micans, Alexandrium tamarense (AT-6, non-PSP producer), Alexandrium lusitanicum, Alexandrum tamarense (ATHK) and Heterosigma akashiwo were studied against rotifer Brachionus plicatilis under laboratory conditions. The results show that P. donghaiense, P. globosa, P. micans, A. tamarense (AT-6), or A. lusitanicum could maintain the individual survival and reproduction, as well as the population increase of the rotifer, but the individual reproduction would decrease when exposed to these five algae at higher densities for nine days; H. akashiwo could decrease the individual survival and reproduction, as well as population increase of the rotifer, which is similar to that of the starvation group, indicating that starvation might be its one lethal factor except for the algal toxins; A. tamarense (ATHK) has strong lethal effect on the rotifer with 48h LC50 at 800 cells/mL. The experiment on ingestion ability indicated by gut pigment change shows that P.donghaiense, P. globosa, P. micans, A. tamarense (AT-6) and A. lusitanicum can be taken by the rotifers as food, but A. tamarense (ATHK) or H. akashiwo can be ingested by the rotifers. The results indicate that all the indexes of individual survival and reproduction, population increase, gut pigment change of the rotifers are good and convenient to be used to reflect the toxicities of HAB species. Therefore, rotifer is suggested as one of the toxicity testing organisms in detecting the toxicity of harmful algae.     

Molecular identification of Prorocentrum （Dinophyceae） species

A fragment of a large sub-unit ribosomal DNA (LrDNA) of 12 strains of Prorocentrum species was amplified by polymerase chain reaction (PCR). The PCR products were digested by 3 restriction endonucleases (Cfo Ⅰ, Hae Ⅲ, and RSA Ⅰ) and then resolved in agarose gels. Results show that different species had different RFLP patterns, except for P arcuatum (ME 131), which had the same pattern to P. micans (ME 160 and 04).The same fragment of 19 strains of the genus was also amplified and subjected to denaturing gradient gel electrophoresis (DGGE). 11 different patterns were resolved. Different cultures of a same species had the same pattern. The results of RFLP and DGGE analyses showed that eight newly isolated epibenthic Prorocentrum species were different from each other, and also from other cultured ones examined in this study. P arcuatum(MEI32) could not be differentiated from P. micans (MEI60 and 04), it was probably mis-identified, since they are quite different morphologically. P. redfieldii (MEI38) could also not be distinguished form P. triestinium(MEI32), it should be regarded as a synonym ofP. triestinium. Unexpectedly, a restriction site was found in P.micans, compared with previous sequence data.     

Effects of iron and humic acid on competition between Microcystis aeruginosa and Scenedesmus obliquus revealed by HPLC analysis of pigments

Iron is a vital micro nutrient for growth of bloom-forming Microcystis aeruginosa and competition with other algae,and its availability is affected by humic acid.The effect of iron and humic acid on growth and competition between M.aeruginosa and Scenedesmus obliquus was assessed.The results showed the growth of M.aeruginosa and S.obliquus in mono-cultures was inhibited by humic acid at low iron concentrations(0.01 mg/L);the maximum inhibition ratios were 67.84% and 38.31%,respectively.The inhibition of humic acid on the two species was significantly alleviated when iron concentrations were1.00 mg/L,with the maximum inhibition rate reduced to 5.82% for M.aeruginosa and to 23.06% for S.obliquus.S.obliquus was the dominant species in mixed cultures,and the mutual inhibition between M.aeruginosa and S.obliquus at low iron concentration was greater than that at high iron concentration.The inhibition of S.obliquus on M.aeruginosa was reduced at low iron concentrations;it increased at high iron concentrations,as concentrations of humic acid rose.     

Experimental Study on the Interspecific Interactions Between the Two Bloom-Forming Algal Species and the Rotifer Brachionus plicatilis

The interspecific interactions between the rotifer Brachionus plicatilis and two harmful algal blooms(HAB) species were investigated experimentally by single culture method. B. plicatilis population and the growth of the two algae were compared at different algal cell densities. The results demonstrated that the B. plicatilis obtained sufficient nutrition from Prorocentrum donghaiense to support net population increase. With exposure to 2.5×104 cells mL-1 of P. donghaiense,the number of B. plicatilis increa...     

Allelopathic effects of mixotrophic dinoflagellate Akashiwo sanguinea on co-occurring phytoplankton: the significance of nutritional ecology

Blooms of Akashiwo sanguinea frequently break out around the world, causing huge economic losses to the aquaculture industry and seriously damaging coastal ecosystems. However, the formation mechanisms of A. sanguinea blooms remain unclear. We investigated the allelopathic effects of A. sanguinea on multiple phytoplankton species, explored the mode of allelochemicals action and the way of nutrient factors regulation of the allelopathic activity. Results show that strains of A. sanguinea could inhibit the growth of co-occurring phytoplankton including Scrippsiella trochoidea, Phaeocystis globosa, and Rhodomonas salina, but inhibition of Prorocentrum micans was not obvious. The inhibition rates on phytoplankton were positively correlated with the cell densities of A. sanguinea. The highest inhibition rate of 94% on R. salina was for A. sanguinea CCMA256 culture of 2 000 cells/mL at 72 h. We observed that cells of S. trochoidea, Ph. g lobosa, and R. sali na were lysed when co-cultured with A. sanguinea, with the shortest time for S. trochoidea. Additionally, the growth rates of A. sanguinea were promoted by coculturing with S. trochoidea, Ph. globosa, and R. salina. Four components of A. sanguinea culture were all able to inhibit growth of R. salina:the strongest inhibitory effect was found in the sonicated culture, followed by whole-cell culture, filtrates of sonicated culture, and filtrate culture. The crude extract of A. sanguinea culture also lysed cells of R. salina, and the inhibition rates on R. salina increased with the increasing dose of crude extract. It was shown that both nutrient enrichment and nitrogen:phosphorus ratio imbalance enhanced remarkably the allelopathic activity of A. sanguinea. The highest inhibition rate on R. salina of 70% occurred in A. sanguinea JX13 treatment at 2 000 cells/mL under high nutrient condition in 48 h. In JX14 treatment at 2 000 cells/mL for N:P of 10:1, the inhibition rate increased by 1.7 times of that for N:P of 20:1. In addition, the allelopathy of A. sanguinea could not only be a competitive strategy but also a nutrition strategy, playing an important role in formation and/or maintenance of blooms of the mixotrophic dinoflagellate A. sanguinea.     

Application of rotifer Brachionus plicatilis in detecting the toxicity of harmful algae

The toxicity of seven major HAB (harmful algal bloom) species/strains, Prorocentrum donghaiense, Phaeocystis globosa, Prorocentrum micans, Alexandrium tamarense (AT-6, non-PSP producer), Alexandrium lusitanicum, Alexandrum tamarense (ATHK) and Heterosigma akashiwo were studied against rotifer Brachionus plicatilis under laboratory conditions. The results show that P. donghaiense, P. globosa, P. micans, A. tamarense (AT-6), or A. lusitanicum could maintain the individual survival and reproduction, as well as the population increase of the rotifer, but the individual reproduction would decrease when exposed to these five algae at higher densities for nine days; H. akashiwo could decrease the individual survival and reproduction, as well as population increase of the rotifer, which is similar to that of the starvation group, indicating that starvation might be its one lethal factor except for the algal toxins; A. tamarense (ATHK) has strong lethal effect on the rotifer with 48h LC₅₀ at 800 cells/mL. The experiment on ingestion ability indicated by gut pigment change shows that P. donghaiense, P. globosa, P. micans, A. tamarense (AT-6) and A. lusitanicum can be taken by the rotifers as food, but A. tamarense (ATHK) or H. akashiwo can be ingested by the rotifers. The results indicate that all the indexes of individual survival and reproduction, population increase, gut pigment change of the rotifers are good and convenient to be used to reflect the toxicities of HAB species. Therefore, rotifer is suggested as one of the toxicity testing organisms in detecting the toxicity of harmful algae. Supported by the Knowledge Innovation Program of Chinese Academy of Sciences (No. KZCX2-YW-208), National Natural Science Foundation of China (No. 40821004, U0733006) and National Basic Research Program of China (973 Program, No. 2001CB409700)     

Production of Pacific White Shrimp Polycultured with Swimming Crab at Different Densities,and Nutrient Budget in the Enclosure System

This study was to evaluate the effect of stocking densities on the nitrogen and phosphorus budgets for a polyculture of the crab Portunus trituberculatus and the Pacific white shrimp Litopenaeus vannamei.The shrimps(initial weight,0.012 g)were cultured at a density of 45 shrimp m^-2,and juvenile crabs(initial weight,0.024 g)were cultured at five densities of 0,3,6,9,and 12 crabs m^-2.The treatments were grouped as C0S45,C3S45,C6S45,C9S45,and C12S45,respectively.Water quality parameters,growth of shrimp and crabs,and nitrogen and phosphorus budget were measured.The results indicated that the shrimp performances in polyculture treatments C3S45 and C6S45 were superior to those in the crab-free treatment(C0S45).The crab in treatments C3S45 and C6S45 exhibited a significantly higher final mean weight and carapace width/length than those in treatments C9S45 and C12S45.The final size and survival of crabs had a negative correlation with the increasing crab stocking density.The contents of total phos-phorus and total nitrogen and the comprehensive contamination index values were higher in the C9S45 and C12S45 treatments than in the other treatments.The conversion ratios of nitrogen for crab and shrimp growth in treatment C3S45 were significantly higher than those in the crab-free treatment.These findings indicate that polyculturing shrimp with crabs at suitable densities can improve productivity,profitability,nutrient utilization,and the environmental quality.From the 60-day treatments,the optimal culture densi-ties were 3-6 crabs m^-2 and 45 shrimps m^-2.     

Spatial pattern analysis and associations of different growth stages of populations of Abies georgei var.smithii in Southeast Tibet,China

Abies georgei var.smithii is an important plant species in Southeast Tibet,China.It has high ecological value in terms of biodiversity protection,as well as soil and water conservation.We analyzed the spatial pattern and associations of A.georgei var.smithii populations at different growth stages by using Ripley's L function for point pattern analysis.The diameter structure was a nearly reverse 'J' shape.The amount of saplings and medium-sized trees accounts for a large part of the entire population,suggesting a high regeneration rate and an expanding population.In the transition from saplings to medium trees or to large trees,saplings show a significant aggregation distribution at small scales,while medium trees and large trees show a random distribution.There are significant inverse associations between saplings and medium trees and large trees at small scales,while there are no obvious associations between medium trees and large trees.The natural regeneration was affected by interspecific competition,and it was also affected by intraspecific competition.The joint effects of biological characteristics and environmental factors contribute to the spatial distribution pattern and associations of this A.georgei var.sm ithii population.     

APPLICATION OF CLAYS TO REMOVAL OF RED TIDE ORGANISMS Ⅱ.COAGULATION OF DIFFERENT SPECIES OF RED TIDE ORGANISMS WITH MONTMORILLONITE AND EFFECT OF CLAY PRETREATMENT

Study on the coagulation of four species of red tide organisms(Nitzschia pungens,Skeletonema costatum,Prorocentrum minimum and Noctiluca scintillans)with montmorillonite,and the effect ofmontmorillonite pretreatment on the coagulation shows that the capability for montmorillonite to coagu-late with them is in the order:N.pungens>S.costatum>P.minimum>N.scintillans.Thecoagulation is discussed from the aspects of the structure,shape,size,movement,habit,etc.of differ-ent species and the results are explained theoretically.The experimental results also indicate that the treat-ment of montmorillonite with acid can enhance its coagulating capability.This is due to the fact that Al(OH_2)_6~(+3),exchanged from the clay lattice by hydrogen ion H~+,forms hydroxy-aluminum polymers on thesurface of the montmorillonite.The hydroxy-aluminum polymers positively charge and increase the positivecharacteristic of the clay surface,and also serves as a bridge between adjacent surfaces of particles.Thesetwo functions enhance     

Performance of ecological restoration in an impaired coral reef in the Wuzhizhou Island,Sanya, China

Coral restoration is becoming popular to help restoring degraded coral reefs.However,few studies have tried to monitor the long-term recovery of coral reefs,which makes it difficult to assess the performance of the restoration.We monitored the growth of three transplanted Acropora corals and naturally-attached Pocillopora damicornis on artificial reefs(ARs) from October 2014 to September 2018 during which there were several attacks of typhoons.Results show that two staghorn Acropora species had the highest growth rate s(11.0-12.1 cm/a),followed by table coral A.divaricate(5.6 cm/a) and P.damicornis(4.8 cm/a).A linear growth pattern was found for the three Acropora species;the pattern gradually slowed in P.damicornis.There was a strong interspecific competition for space among the corals on ARs,and it led to the sharply declined occurrence of slow-growing P.darmicornis colonies in 2017.Coral recovery was successful at the Wuzhizhou Island and quickly increased AR complexity.However,the ARs made of metal frames fail to resist the direct attack from a catastrophic typhoon.Therefore,concrete and environmentalfriendly materials should be used in future restoration.This study is the first report on long-term monitoring and assessment of coral reef restoration in China.The results offer future guide of reef restoration for impaired coral reefs in regions easily affected by typhoons.     

Ecological effects of co-culturing the sea cucumber Apostichopus japonicus with the Chinese white shrimp Fenneropenaeus chinensis in an earthen pond

Using net enclosures in an earthen pond, we established three culture treatments with the sea cucumber Apostichopus japonicus and the Chinese white shrimp Fenneropenaeus chinensis : monoculture of sea cucumbers(C), monoculture of shrimp(S), and co-culture of the two species(CS). We measured levels of suspended particulate matter in the water column; total organic matter, total organic carbon, total nitrogen, and carbon/nitrogen ratios in both settling particles and the sediment; and chlorophyll a levels in the sediment. We then compared these variables between the three treatments. We also examined growth, survival, and yield of the two species in the different treatments. From June to September, the mean monthly suspended particulate matter sedimentation rates in the CS and S treatments were significantly( P 0.05) greater than those in the C treatment. From August to November, the mean monthly total organic matter, total organic carbon, total nitrogen, and chlorophyll a contents in the sediment in the CS and S treatments were significantly( P 0.05) greater than those in the C treatment. Final wet weight, specific growth rate, survival rate, and total yield of sea cucumbers in co-culture were all significantly greater than those of sea cucumbers in monoculture. There were no significant differences among any of these variables for shrimp reared in the two systems. The bioturbation of the sediment and fecal production of the shrimp likely supplied natural food for the sea cucumbers. Co-culture of the two species is a viable option for increasing yield per unit area, maximizing use of the water body, and diversifying crop production.     

Experimental study on the interspecific interactions between the two bloom-forming algal species and the rotifer Brachionus plicatilis

The interspecific interactions between the rotifer Brachionus plicatilis and two harmful algal blooms (HAB) species were investigated experimentally by single culture method. B. plicatilis population and the growth of the two algae were compared at different algal cell densities. The results demonstrated that the B. plicatilis obtained sufficient nutrition from Prorocentrum donghaiense to support net population increase. With exposure to 2.5×10⁴ cells mL⁻¹ of P. donghaiense, the number of B. plicatilis increased faster than it did when exposed to other four algal densities (5, 10, 15 and 20 ×10⁴ cells mL⁻¹), and the increase rate of B. plicatilis population (r) at this algal density was 0.104 ± 0.015 rd⁻¹. Cell densities of P. donghaiense decreased due to the grazing of B. plicatilis. In contrast, Heterosigma akashiwo had an adverse effect on B. plicatilis population and its growth was largely unaffected by rotifer grazing. In this case, B. plicatilis population decreased and H. akashiwo grew at a rate similar to that of the control.