Allelopathic Interactions Between the Tropical Macrophyte Enhalus acoroides and Epibenthic HAB Dinoflagellate Prorocentrum concavum

A benthic harmful dinoflagellate bloom caused by Prorocentrum concavum occurred at Xincun Bay,a lagoon characterized by a tropical seagrass ecosystem in the southern China,in summer 2018.Both abiotic and biotic factors may affect the abundance dynamics of P.concavum.One of the biotic factors,allelopathy,is known to be especially common among aquatic species and is suggested to be an economical and environmentally-friendly way to eliminate Benthic Harmful Algal Blooms(BHABs).To investigate the possible allelopathic interactions between seagrasses and P.concavum,a field survey was conducted to study the cell densities of P.concavum on four major substrates over 12 months.In laboratory,fresh Enhalus acoroides leaves and a crude aqueous extract of dry E.acoroides leaves were added to the culture of P.concavum respectively to assess possible effects on the growth and photosynthesis activities of P.concavum cells.Our results showed that the average abundance of P.concavum on E.acoroides leaves was statistically lower than that on the sediment outside the seagrass meadow and that on Thalassia hemperichii leaves.Both the growth and photosynthesis activities of P.concavum cells were inhibited in the two experiments,which can be attributed to the release and production of allelochemicals by E.acoroides.Our results offer new insights into the interaction between the submerged seagrass E.acoroides and the benthic harmful algal bloom dinoflagellate P.concavum,which can influence the abundance dynamics of P.concavum and provide an alternative for reducing potential threat of BHABs.

Characterization of the Complete Mitochondrial Genome of Arius dispar(Siluriformes: Ariidae) and Phylogenetic Analysis Among Sea Catfishes

The mitochondrial genome(mitogenome) was 16792 bp in length, containing 13 protein coding genes(PCGs), two rRNA genes(12 S rRNA and 16 S rRNA), 22 tRNA genes, and two main non-coding regions. Among these 37 genes, 28 genes were encoded on the heavy strand, while 9 genes were transcribed on the light strand. The non-coding regions of A. dispar included a control region, a light strand replication and another 11 intergenic spacers. The CR of A. dispar contained 8 conserved sequence blocks(CSBs), a termination-associated sequence(TAS) and a pyrimidine tract. Phylogenetic analysis based on 12 PCGs revealed that A. dispar was genetically closest to Arius arius. The families Schilbeidae, Claroteidae, Mochokidae, and Ariidae formed a closely evolved clade. Molecular information from this research introduces mitogenomice data of A. dispar and suggests the phylogenetic relationships among Siluriformes.

赤潮生物伊姆裸甲藻(Gymnodinium impudicum)毒性和温度适应初步研究

2021年8月26日,我国广东省海门湾海域暴发了一起裸甲藻赤潮,现场藻细胞密度达3.39×10^(3)cells·mL^(−1).本文对该次赤潮肇事种进行了形态学与系统发育学分析,对现场赤潮水样进行了海洋青鳉鱼(Oryzias melastigma)48 h急性生物毒性分析,对赤潮藻纯培养细胞进行了卤虫(Artemia salina)48 h急性生物毒性分析、溶血活性测定以及最佳生长温度研究.结果表明,此次赤潮肇事种为伊姆裸甲藻(Gymnodinium impudicum).急性生物毒性实验结果表明,赤潮海水对海洋青鳉鱼无明显致死效应,海洋青鳉鱼48 h内游动正常,无异常反应.该藻纯培养藻种对卤虫具有一定的致死效应,藻密度4.32×10^(3)cells·mL^(−1)时,48 h卤虫死亡率为35%.溶血活性检测结果表明,该藻溶血活性较低,藻细胞密度为3.66×10^(3)cells·mL^(−1)时,溶血活性百分数为26.7%.实验室纯培养下,该藻对温度适应性较强,在20℃、25℃、30℃下均可生长,最高密度达(2.35—2.54)×10^(4)cells·mL^(−1).25℃时藻细胞比生长速率最高(μmax=0.371);33℃不适宜该藻增殖,此温度下,藻密度长时间维持在(1.40—6.85)×10^(2)cells·mL^(−1).本次赤潮为我国南海海域首次报道伊姆裸甲藻赤潮,该藻的潜在危害及赤潮灾害效应值得进一步关注.

微量元素锰对底栖甲藻热带库里亚藻(Coolia tropicalis)生长及叶绿素荧光特性的影响

以热带库里亚藻(Coolia tropicalis)为研究对象,在不同锰浓度(0、1、5、10、50μmol·L^–1)的人工海水培养15d,利用叶绿素荧光动力学技术研究了其生长和光合作用对不同锰环境的响应。结果表明:1)比生长速率(μ)和最大相对电子传递速率(rETRmax)与锰浓度均呈指数关系且对锰胁迫具有相同程度的响应;2)锰浓度至少大于1μmol·L^–1才能维持热带库里亚藻正常的光合作用活性,当锰浓度低于该浓度时,光合作用活性(Fv/Fm)在6d后开始下降,而单位反应中心吸收光能(ABS/RC)和热能耗散(DI0/RC)升高;两个反应中心之间的电子传递(φE0)及生长并未受影响,表明此阶段锰缺乏只影响活性光反应中心数量并提高热耗散途径;当锰缺乏延长至15d时,胁迫作用显现(F0上升)并且电子传递(φE0)和生长受到抑制,这阶段锰缺乏使光反应中心关闭且电子传递受阻;3)锰缺乏的修复损伤比(r/k)并未降低,表明锰缺乏并未影响热带库里亚藻的光保护能力。

Temporal and Spatial Variations of Abundance of Phycocyaninand Phycoerythrin-Rich Synechococcus in Pearl River Estuary and Adjacent Coastal Area

Three surveys were carried out in Pearl River Estuary and adjacent coastal area in May, August, and November, 2013, to investigate the temporal and spatial variations of abundance of phycoerythrin-rich Synechococcus(PE-rich SYN) and phycocyanin-rich Synechococcus(PC-rich SYN). The effects of environmental factors on the alternation of the different Synechococcus groups were also elucidated. PE-rich SYN was detected in three surveys, whereas PC-rich SYN was detected in May and August, but not in November. The highest abundances of PE-rich SYN and PC-rich SYN were recorded in August and May, with mean values of 74.17×103 and 189.92×103 cells m L-1, respectively. From May to November, the relative abundance of PE-rich SYN increased, whereas that of PC-rich SYN declined. PE-rich and PC-rich SYN presented similar horizontal distributions with high abundance in the southern estuary in May, and in the western estuary in August. The abundances of PE-rich and PC-rich SYN were high at 27–32℃and salinity of 10–20. PC-rich SYN was not detected at < 24℃, and PC:PE-rich SYN decreased in abundance with salinity increase. When less than 20 mg L-1, suspended particulate matter(SPM) was helpful for Synechococcus growth. PE-rich SYN decreased in abundance when the concentration of dissolved inorganic nitrogen increased in May and November, and the concentration of phosphate increased in November. However, PC-rich SYN abundance and nutrients showed no correlation. Principal component analysis and regression analysis indicated that PE-rich SYN significantly correlated with the principal components that were affected by environmental factors.

A re-investigation of the bloom-forming unarmored dinoflagellate Karenia longicanalis(syn.Karenia umbella)from Chinese coastal waters

The dinoflagellate genus K arenia is known for recurrent harmful blooms worldwide. However, species diversity of the genus is generally overlooked owing to the difficulty of identifying small unarmored dinoflagellates. We have established four clonal cultures of K arenia longicanalis isolated from the type locality, Hong Kong harbor(strain HK01) and other three locations along the Chinese coasts(strains YB01, DT01, and NJ01). The morphology of the strain was studied by light and scanning electron microscopy(LM and SEM) and the pigment composition analyzed by high-performance liquid chromatography. We provide the first molecular data of K. longicanalis based on the large subunit(LSU) rRNA gene sequence and internal transcribed spacer(ITS). The four strains showed identical LSU rDNA sequences with a similarity of 99.4% to the holotype of K arenia umbella(strain KUTN05) from Australia. In the ITS phylogeny, the sequence of K. umbella branched between the Chinese strains of K. longicanalis. A careful comparison of the morphology of K. longicanalis and K. umbella reveals the similarity in the diagnostic characters. Diff erences may appear due to the sample treatment for SEM. We conclude that K. umbella is a junior synonym of K. longicanalis.

中国西沙群岛底栖甲藻热带库里亚藻(Coolia tropicalis)的形态学、系统发育及毒性研究

库里亚藻(Coolia)是一类广泛分布且具有生物毒性的海洋底栖甲藻。本研究对近年来在中国南海西沙群岛海域采集分离的4株库里亚藻,通过光镜及电镜下的形态学观察,并结合基于核糖体大亚基(large subunit,LSU)rDNA(D1-D3)和内部转录间隔区(internal transcribed spacer,ITS)的序列进行系统发育分析,鉴定该4个株系为热带库里亚藻(Coolia tropicalis)。在卤虫(Artemia salina)生物毒性试验中,热带库里亚藻不同株系毒素提取液对卤虫幼虫表现出了毒性差异,XS554株系的48h半致死浓度(LC50)为1.42mg·mL^–1(约相当于1.1×10^5cells·mL^–1),5XS15株系的LC50为1.92mg·mL^–1(约相当于1×10^5cells·mL^–1)。

Effects of Ultraviolet(UV)Radiation on Outdoor-and Indoor-Cultured Prorocentrum lima,a Toxic Benthic Dinoflagellate

The effects of different types of ultraviolet(UV)radiation(UVR,wavelength=280-400 nm)and light intensities on cell growth,pigment composition,UV-absorbing compounds(UVACs),and chlorophyll a(Chl a)fluorescence were studied in dinoflag-ellate Prorocentrum lima cultured outdoors for 16 days and indoors for 18 days.In the outdoor experiment,UVA radiation(320-400 nm)increased the growth rate of this dinoflagellate when solar light intensities were<12%;decreased growth rates were observed when intensities were>12%.Exposure to UVB radiation(280-320 nm)alleviated the negative effects of UVA.In the indoor ex-periment,UVA and low doses of UVB enhanced growth rates.Addition of low doses of UVB to UVA exposure resulted in higher contents of Chl a and photoprotective pigments compared with UVA exposure only.The results of both experiments showed that UVB is the primary signal of UVAC synthesis.High-dose UVB exposure accelerated growth rates when UVAC contents were maintained at high levels,suggesting that the latter plays a key role in UVR damage protection.Furthermore,the repair rate was en-hanced by UVB exposure after 16 days of culture.This study confirms the positive effects of UVA and UVB on the growth of P.lima,with the latter enhancing the photoprotective and recovery pathways of the species.

Grazing and performance of the copepod Pseudodiaptomus poplesia on a Chinese strain of Aureococcus anophagefferens

Brown tides have recurred in estuary areas globally,but trophic interactions between the causative species Aureococcus anophagefferens and planktonic copepods remain poorly understood.In this study,we investigated performance（ingestion,growth,development and reproduction） of the planktonic copepod,Pseudodiaptomus poplesia,offered either mono-algal or mixed-algal diets containing a Chinese strain of A.anophagefferens.A typical Michaelis-Menten pattern existed between ingestion rate and food level when copepod fed on the monoalgal diet of this species.Nauplii exhibited the highest maximum ingestion rate（Imax） than copepodids and adult females.In addition,Imax value was higher in nauplii feeding on A.anophagefferens than on Skeletonema costatum.When fed mixtures of A.anophagefferens and S.costatum,P.poplesia selected against A.anophagefferens cells,but less strongly at the naupliar stage.Nauplii did not undergo metamorphosis and died at late naupliar stages feeding on A.anophagefferens alone,similar to those under starvation.Furthermore,the presence of A.anophagefferens greatly reduced the reproduction rate of females in mixtures but did not influence the growth rate of copepodids.These results suggest that P.poplesia nauplii may exert grazing pressure on A.anophagefferens population during a brown tide,which,however,may not be persistent because of copepod population decline.

Distribution and germination of viable diatom resting stage cells in sediments of the East China Sea

The abundance and temporal patterns of viable diatom resting stage cells in sediments of the East China Sea in 2006 have been investigated.The abundance of viable resting stages was enumerated with the most probable number（MPN） technique.Overall,25 diatom species（including varieties） belonging to 16 genera were detected.Viable resting stage cells were common,on the order of 103 to 106 cells/g dry mass.The abundant taxa included Skeletonema marina,S.dohrnii,Chaetoceros curvisetus and Thalassiosira spp.,with Skeletonema accounting for 83.3% of the cell.The effects of temperature（10,15,20,25 ℃）,salinity（20,25,30,35 psu） and light intensity（0,300,4 000,8 000 lux） on the germination of resting stages in sediment samples were also determined.The results showed that light intensity had a significant positive effect on the germination of diatom resting stage cells（p 〈0.01） and that diatoms could not germinate in darkness.Temperature and salinity had no noticeable effects on the germination.The present study suggests that there are abundant diatom resting cells in sediments of the East China Sea,which could serve as a ＂seed bank＂ in the phytoplankton population succession and contribute to the initiation of algal blooms.

Seasonal variation of size-fractionated phytoplankton in the Pearl River estuary

To investigate the dynamics of phytoplankton size structure in the Pearl River estuary, concentrations of size-fractionated chlorophyll a (Chl a) were determined during four cruises carried out in 2008 and 2010. The distribution of Chl a in this geographical location showed a high degree of temporal variation. Chl a concentrations were highest in autumn, approximately three times higher than those in summer and winter. Microphytoplankton was the dominant contributor, accounting for 66.9% of the Chl a concentration in autumn 2008. In summer and spring 2008, nano-sized cells dominated the phytoplankton population throughout the study region. During the winter cruise, two different areas of water were found, characterized by (1) low salinity and high nutrient content and (2) high salinity and low nutrient content; nano- and picophytoplankton co-dominated the first area, while microphytoplankton dominated the second. It is arguable that grazing could have played a role in determining phytoplankton community size structure in winter. Nutrient concentrations were assumed not to limit phytoplankton growth during the investigation period. Size-differential capacity in competing for the resources available under different hydrodynamic conditions seemed to be the major factor in determining seasonal variation in the structure of the phytoplankton communities. High N:P ratios in the Pearl River estuary had major implications for nutrient pollution control. Our results indicated that studies of phytoplankton size structure provide greater insight into phytoplankton dynamics and are necessary to better manage water quality in the Pearl River estuary.