抑藻细菌HSY-03的分离、鉴定及对赤潮异弯藻生长的影响

从福建云霄红树林区分离筛选出一株对赤潮异弯藻(Heterosigma akashiwo)具有较强抑藻作用的细菌,命名为HSY-03。结合16S rDNA序列分析,该菌与芽孢杆菌属(Bacillus sp.)同源性高达99.0%。通过抑藻方式研究发现菌株是通过分泌胞外活性物质抑藻,属于间接杀藻;胞外活性物质为非多糖、非脂肪、非蛋白类化合物,具有较好的光、热和酸碱稳定性;对供试13株赤潮藻未表现出溶藻效果,表明该菌株抑藻具有一定的种属特异性。菌株HSY-03抑藻效果具有浓度效应,初始终浓度高于5.0%抑藻效果较好。不同生长时期菌株HSY-03对赤潮异弯藻均表现出较好的抑藻效果,但菌株处于稳定期和衰亡期时抑藻效果最好。

中国胶州湾赤潮异弯藻rDNA ITS区序列分析

测定了采自中国胶州湾赤潮异弯藻X2藻株18S rDNA ITS区基因序列,结合GenBank中下载的37条同源序列,分析序列特征并构建分子系统树。发现534 bp序列中有可变位点16个、简约信息位点1个,可变位点和简约信息位点分别占全序列的3.0%和0.19%,序列间相似性为97%,A+T含量(47.8%)略小于C+G含量(52.2%)。在分子系统树上,全部序列聚类在一起,遗传距离在0.0000~0.0242之间,说明全部赤潮异弯藻遗传多样性极低。赤潮异弯藻的生长和繁殖受到外界环境因子的较大制约,而人为因素如船只压舱水等则是其传播的主要途径。

大连湾赤潮生物──赤潮异弯藻

于1985，1986和1987三年的夏季在辽宁省大连湾采集赤潮生物──赤潮异湾藻，以相差显微镜和扫描电镜进行了形态观察和分类研究；同时述及其分类沿革及至今仍存在的争议，结合本种在大连湾的生态特点简要地综述了其在世界上的分布、生理宗、昼夜垂直移动、营养摄取以及细胞分裂周期和种群繁殖等。结果表明，在温带近海夏、秋季赤潮异弯藻的生长率最高，冬季休眠于海底；温度是限制其复苏的主要因子。本种昼夜都能摄取营养，生态效益较高是其易于形成赤潮的动力。海水中的N，Fe和Mn的含量是影响本种赤潮发生的营养因子。

羧甲基纤维素钠限制浮游藻类运动的实验研究

传统压载水镜检中常使用一些化学试剂来固定压载水水样中的浮游藻类，传统所使用的海藻酸钠及聚乙烯醇溶液限制浮游藻类存在一些缺点，而根据这些缺点，一般会使用羧甲基纤维素钠溶液来限制浮游藻类的运动。其色泽较好，粘稠度也适中。

Effect of nitrogen to phosphorus ratios on cell proliferation in marine micro algae

The ratio of nitrogen/phosphorus （N/P） is known to affect cell proliferation of some marine micro algae. We evaluated the effect of N/P ratios on the proliferation and succession of phytoplankton using five marine micro algae species. We used two sources of nitrogen, NH4Cl （N1） and urea （N2）, and a single source of phosphorous, NaH2PO4（P）. The optimal N/P ratio that differed among the five species was affected by the source of nitrogen, being as follows （N1/P, N2/P in order）： Thalassiosira sp. （30/1, 20/1）, Heterosigma akashiwo （30/1, 30/1）, Chroornonas salina （20/1, 30/1）, Chaetoceros gracilis （40/1, 60/1）, and A lexandrium sp. （10/1, 30/1）. Thus, the source of nitrogen must be considered when analyzing the N/P ratio. Our results provide insight for predicting phytoplankton succession in coastal waters and may be used to forecast the potential risk of harmful algal blooms.

Allelopathic eff ects of macroalga Corallina pilulifera on the red-tide forming alga Heterosigma akashiwo under laboratory conditions

Over the past few years, harmful algal blooms （HABs）, such as red tides, have been frequently observed in coastal zones worldwide. The natural allelopathic interactions among macroalgae and red tide microalgae can alter the structure and succession of aquatic ecosystems. We investigated the influence of four environmental factors （temperature, salinity, light, and pH） on the allelopathic effects of the macroalgae Corallina pilulifera on red-tide forming Heterosigma akashiwo under laboratory conditions. Each of the factors had four levels： temperature （15, 20, 25, and 30℃）, salinity （10, 20, 30, and 40）, light （20, 100, 200 and 400 gmol/（m2.s））, and pH （5.5, 7, 8.5, and 10. Two-factor experiments were designed for each two environmental factors, with six combination treatments （temperature-salinity, temperature-light, temperature-pH, salinity-light, salinity-pH, and light-pH）. Results showed that the allelopathic effect was significantly influenced by temperature, salinity, light, and pH. As single factors, the low temperature （15 ℃）, low salinity （10）, high-intensity light （400umol/（m2.s））, and high pH （10） treatments substantially enhanced the allelopathic effect. The strongest allelopathic effect of C. pilulifera on H. akashiwo was observed under the following treatments： 15℃ and salinity of 40, 25℃ and pH 10, 25℃ with medium- to high-intensity light at 200-400 umol/（m2.s）, 400umol/（m2.s） and salinity of 10, 400 gmol/（m2·s） and pH 10, and pH 10 with a salinity of 40.

A Comparative Study of the Sensitivity of F_v/F_m to Phosphorus Limitation on Four Marine Algae

We studied the effects of nitrogen （N） and phosphorus （P） supply on Fv/Fm （maximal quantum yield of photosystem Ⅱ） in the algae Chaetoceros debilis, Dicrateria inornata, Platymonas subcordiformis and Heterosigma akashiwo to determine the sensitivity of Fv/Fm to P-limitation of the four species. Obvious decrease of Fv/Fm value was monitored in periods of P-depletion, the decrease showing different magnitudes among algal species. A more clear decrease of Fv/Fm in Platymonas subcordiformis and Heterosigma akashiwo was observed, compared with that in Chaetoceros debilis and Dicrateria inornata. After the re-supply of P, the index Fv/Fm of the four species all recovered quickly in 24h. Cell division was maintained and chlorophyll content continued to increase until the end of the experiment in Platymonas subcordiformis and Heterosigma akashiwo, while in Chaetoceros debilis and Dicrateria inornata, the division stopped in the later period when the growth of organisms came into the stationary phase. The most obvious respond of chlorophyll content to P-additions was observed in Heterosigma akashiwo culture in 24 h. The sensitivity of Fv/Fm to nutrient limitations is different among algal species, and much should be done to improve the application of this index.

Effect of CO_2 enrichment on competition between Skeletonema costatum and Heterosigma akashiwo

We investigated the effect of CO2 enrichment and initial inoculum density on competition between Skeletonema costatum and Heterosigma akashiwo,two common algae seen in algal blooms.The initial inoculum density(0.2×104,0.4×104,0.8×104 cells/ml) had a significant effect on population growth and competition between H.akashiwo and S.costatum.The time required for population growth to reach the exponential growth phase and stationary phase decreased significantly as the initial density increased.When the two species were cultured together,S.costatum tended to outcompete H.akashiwo,especially when present at higher initial ratios.CO_2 enrichment(5 000μl/L CO_2) increased the maximum population density and carrying capacity of H.akashiwo but decreased these measures for S.costatum.Thus,CO_2 enrichment favored the growth of H.akashiwo over S.costatum.

Fractal dimensions of flocs between clay particles and HAB organisms

The impact of harmful algal blooms （HABs） on public health and related economics have been increasing in many coastal regions of the world. Sedimentation of algal cells through flocculation with clay particles is a promising strategy for controlling HABs. Previous studies found that removal efficiency （RE） was influenced by many factors, including clay type and concentration, algal growth stage, and physiological aspects of HAB cells. To estimate the effect of morphological characteristics of the aggregates on HAB cell removal, fractal dimensions were measured and the RE of three species of HAB organism, Heterosigma akashiwo, Alexandrium tamarense, and Skeletonema eostatum, by original clay and modified clay, was determined. For all HAB species, the modified clay had a higher RE than original clay. For the original clay, the two-dimensional fractal dimension （D2） was 1.92 and three-dimensional ffactal dimension （D3） 2.81, while for the modified clay, D2 was 1.84 and D3 was 2.50. The addition of polyaluminum chloride （PAC1） lead to a decrease of the repulsive barrier between clay particles, and resulted in lower D2 and D3. Due to the decrease of D3, and the increase of the effective sticking coefficient, the flocculation rate between modified clay particles and HAB organisms increased, and thus resulted in a high RE. The fractal dimensions of flocs differed in HAB species with different cell morphologies. For example, Alexandrium tamarense cells are ellipsoidal, and the D3 and D2 of flocs were the highest, while for Skeletonema costatum, which has filamentous cells, the D3 and D2 of flocs were the lowest.

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 r d-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.

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 pH7 weakened this possibility.Further studies on the allelochemicals responsible for the allelopathy of A.tamarense need to be carried out in future.

Effect of Anthracene on the Interaction Between Platymonas helgolandica var. tsingtaoensis and Heterosigma akashiwo in Laboratory Cultures

Two species of marine phytoplankton, Platymonas helgolandica var. tsingtaoensis and Heterosigma akashiwo, were cul- tivated in bi-algal cultures to investigate the effect of anthracene （ANT） on the interaction between them. Without ANT, H. akashiwo out-competed P. helgolandica at low initial biomass ratios （P. helgolandica （P）： H. akashiwo （H） = 1：4 and 1 ： 1）, but not at the highest （P：H=4：I）. This observation was consistent with the description in Lotka-Volterra two species competition model. It was found that P. helgolandica was excluded at low initial biomass ratios, while the unstable equilibrium between two species was predicted at the highest. For both species, carrying capacity and maximal specific growth rate decreased in bi-algal cultures compared to those in monocultures. H. akashiwo exhibited a higher sensitivity to ANT than P helgolandica. This resulted markedly in a reduced cell den- sity of H. akashiwo but an increased cell density ofP. helgolandica. Carrying capacity ofP. helgolandica was consistently higher in bi-algal cultures with ANT than those without ANT, suggesting that ANT, through the elimination of H. akashiwo, generated the dominance of P helgolandica independently of initial biomass ratios. This study showed a density-dependent effect of harmful alga （H. akashiwo） on dietary alga （P helgolandica）, and indicated that ocean pollutant ANT could induce the succession of marine phytoplankton.