The well-known ciliate, Mesodinium Stein, 1863, is of great importance to marine microbial food webs and is related to the ＂red tides＂. However, it is possibly one of the most confusing ciliate taxa in terms of its ...The well-known ciliate, Mesodinium Stein, 1863, is of great importance to marine microbial food webs and is related to the ＂red tides＂. However, it is possibly one of the most confusing ciliate taxa in terms of its systematic position： either the morphological or the molecular data excluded it from all the other known assemblages or groups. In the current work, the sequences of small subunit ribosomal RNA （SSU rRNA） genes for all isolates available are analysed and an examination of the secondary structure patterns of related groups is carried out. The results indicate that （1） Mesodiniurn invariably represents a completely separated and isolated clade positioned between two subphyla of ciliates with very deep branching, which indicates that they should be a primitive or ancestral group for the subphylum Intramacronucleata; （2） the secondary structure of the SSU rRNA of Mesodinium species is unusual in that, while the secondary structure of V4 in Mesodinium sp. has the deletions common to all litostome ciliates, it has more extensive deletions in helix E23_8 and a longer helix E23_1; （3） combining the phylogenetic and morphological information, we suggest establishing Mesodiniea el. nov., including the order Mesodiniida Grain, 1994, belonging to the subphylum Intramacronucleata.展开更多
High-biomass red tides occur frequently in some semi-enclosed bays of Hong Kong where ambient nutrients are not high enough to support such a high phytoplankton biomass. These high-biomass red tides release massive in...High-biomass red tides occur frequently in some semi-enclosed bays of Hong Kong where ambient nutrients are not high enough to support such a high phytoplankton biomass. These high-biomass red tides release massive inorganic nutrients into local waters during their collapse. We hypothesized that the massive inorganic nutrients released from the collapse of red tides would fuel growth of other phytoplankton species. This could influence phytoplankton species composition. We tested the hypothesis using a red tide event caused by Mesodinium rubrum(M. rubrum) in a semi-enclosed bay, Port Shelter. The red tide patch had a cell density as high as 5.0×10~5 cells L^(-1), and high chlorophyll a(63.71 μg L^(-1)). Ambient inorganic nutrients(nitrate:NO_3^-, ammonium: NH_4^+, phosphate: PO_4^(3-), silicate: SiO_4^(3-)) were low both in the red tide patch and the non-red-tide patch(clear waters outside the red tide patch). Nutrient addition experiments were conducted by adding all the inorganic nutrients to water samples from the two patches followed by incubation for 9 days. The results showed that the addition of inorganic nutrients did not sustain high M. rubrum cell density, which collapsed after day 1, and did not drive M. rubrum in the non-red-tide patch sample to the same high-cell density in the red tide patch sample. This confirmed that nutrients were not the driving factor for the formation of this red tide event, or for its collapse. The death of M. rubrum after day 1 released high concentrations of NO_3^-,PO_4^(3-), SiO_4^(3-), NH_4^+, and urea. Bacterial abundance and heterotrophic activity increased, reaching the highest on day 3 or 4, and decreased as cell density of M. rubrum declined. The released nutrients stimulated growth of diatoms, such as Chaetoceros affinis var. circinalis, Thalassiothrix frauenfeldii, and Nitzschia sp., particularly with additions of SiO_4^(3-) treatments, and other species. These results demonstrated that initiation of M. rubrum red tides in the bay was not directly driven by nutrients.However, the massive inorganic nutrients released from the collapse of the red tide could induce a second bloom in low-ambient nutrient water, influencing phytoplankton species composition.展开更多
采用海面以上光谱测量方法（Above water method）,利用美国FieldSpe Dual VNIR光谱仪测量了丹麦细柱藻、中肋骨条藻、海洋褐胞藻等三种浮游植物赤潮以及红色中缢虫这一原生动物赤潮的离水辐射光谱数据.强调赤潮与正常海水的光谱差异在...采用海面以上光谱测量方法（Above water method）,利用美国FieldSpe Dual VNIR光谱仪测量了丹麦细柱藻、中肋骨条藻、海洋褐胞藻等三种浮游植物赤潮以及红色中缢虫这一原生动物赤潮的离水辐射光谱数据.强调赤潮与正常海水的光谱差异在于687～728 nm波段的特征反射峰,指出了浮游植物赤潮与原生动物赤潮间的显著光谱差异,并认为可据此进行某些赤潮种类的遥感识别.给出了浮游植物赤潮光谱反射峰、吸收峰成因;红色中缢虫这一原生动物引起的水色异常,与其体内的共生藻类及浮游植物色素碎屑有关;其摄食偏好、与藻类的共生特性研究以及藻类常温下的荧光发射特性研究,将有助于加深对于红色中缢虫赤潮光谱成因的认识.展开更多
基金supported by the National Natural Science Foundation of China(31272285,41276139)King Saud University Deanship of Scientific Research(Research Group Project No.RGP-083)Special Foundation B of President of the Chinese Academy of Sciences(Y25102EN00)
文摘The well-known ciliate, Mesodinium Stein, 1863, is of great importance to marine microbial food webs and is related to the ＂red tides＂. However, it is possibly one of the most confusing ciliate taxa in terms of its systematic position： either the morphological or the molecular data excluded it from all the other known assemblages or groups. In the current work, the sequences of small subunit ribosomal RNA （SSU rRNA） genes for all isolates available are analysed and an examination of the secondary structure patterns of related groups is carried out. The results indicate that （1） Mesodiniurn invariably represents a completely separated and isolated clade positioned between two subphyla of ciliates with very deep branching, which indicates that they should be a primitive or ancestral group for the subphylum Intramacronucleata; （2） the secondary structure of the SSU rRNA of Mesodinium species is unusual in that, while the secondary structure of V4 in Mesodinium sp. has the deletions common to all litostome ciliates, it has more extensive deletions in helix E23_8 and a longer helix E23_1; （3） combining the phylogenetic and morphological information, we suggest establishing Mesodiniea el. nov., including the order Mesodiniida Grain, 1994, belonging to the subphylum Intramacronucleata.
基金supported by the Guangdong-National Science Foundation of China (Grant Nos. U1701247)the National Natural Science Foundation of China (Grant Nos. 91328203)+1 种基金the International Science and Technology Cooperation Program of Guangdong (Grant No. 2013B051000042)Xiuxian Song was supported by the National Natural Science Foundation of China (Grant Nos. 50339040 & 40025614)
文摘High-biomass red tides occur frequently in some semi-enclosed bays of Hong Kong where ambient nutrients are not high enough to support such a high phytoplankton biomass. These high-biomass red tides release massive inorganic nutrients into local waters during their collapse. We hypothesized that the massive inorganic nutrients released from the collapse of red tides would fuel growth of other phytoplankton species. This could influence phytoplankton species composition. We tested the hypothesis using a red tide event caused by Mesodinium rubrum(M. rubrum) in a semi-enclosed bay, Port Shelter. The red tide patch had a cell density as high as 5.0×10~5 cells L^(-1), and high chlorophyll a(63.71 μg L^(-1)). Ambient inorganic nutrients(nitrate:NO_3^-, ammonium: NH_4^+, phosphate: PO_4^(3-), silicate: SiO_4^(3-)) were low both in the red tide patch and the non-red-tide patch(clear waters outside the red tide patch). Nutrient addition experiments were conducted by adding all the inorganic nutrients to water samples from the two patches followed by incubation for 9 days. The results showed that the addition of inorganic nutrients did not sustain high M. rubrum cell density, which collapsed after day 1, and did not drive M. rubrum in the non-red-tide patch sample to the same high-cell density in the red tide patch sample. This confirmed that nutrients were not the driving factor for the formation of this red tide event, or for its collapse. The death of M. rubrum after day 1 released high concentrations of NO_3^-,PO_4^(3-), SiO_4^(3-), NH_4^+, and urea. Bacterial abundance and heterotrophic activity increased, reaching the highest on day 3 or 4, and decreased as cell density of M. rubrum declined. The released nutrients stimulated growth of diatoms, such as Chaetoceros affinis var. circinalis, Thalassiothrix frauenfeldii, and Nitzschia sp., particularly with additions of SiO_4^(3-) treatments, and other species. These results demonstrated that initiation of M. rubrum red tides in the bay was not directly driven by nutrients.However, the massive inorganic nutrients released from the collapse of the red tide could induce a second bloom in low-ambient nutrient water, influencing phytoplankton species composition.
