Mimosine, the Allelochemical from the Leguminous Tree Leucaena leucocephala, Selectively Enhances Cell Proliferation in Dinoflagellates

Mimosine, the allelochemical from the leguminous tree Leucaena leucocephala, is toxic to most terrestrial animals and plants. We report here that while mimosine inhibits major phytoplankton groups, it enhances cell proliferation in dinoflagellates. On addition to coastal seawater samples, mimosine is able to confer a growth advantage to dinoflagellates. The use of mimosine will promote the isolation and culture of this group of phytoplankton.     

Microzooplankton grazing and the control of phytoplankton biomass in the Suwannee River estuary,USA

Microzooplankton grazing can have significant impacts on the distribution and abundance of phytoplankton, thereby influencing the frequency and duration of algae blooms. Observations of high ciliate abundances in the Suwannee River estuary, Florida, suggest a significant potential for top-down pressure on the phytoplankton community by microzooplankton. We examined the composition of the microzooplankton and determined grazing mortality losses for phytoplankton within the Suwannee River estuary from 2001 to 2002. Our results indicated grazing mortality rates of 1.4 d⁻¹, equivalent to a loss of up to 76% of phytoplankton standing crop and up to 83% of total daily primary production. The microzooplankton community was primarily composed of ciliates, dinoflagellates, and copepod nauplii. The densities of ciliates in the estuary were comparable to densities reported in highly eutrophic ecosystems (9,400–72,800 ciliates l⁻¹). Grazing pressure on small phytoplankton may be further enhanced because ciliates and small dinoflagellates have growth rates similar to those of phytoplankton, and therefore can keep up with surges in abundance. Handling editor: Judit Padisak     

Parasites and phytoplankton, with special emphasis on dinoflagellate infections

Planktonic members of most algal groups are known to harbor intracellular symbionts, including viruses, bacteria, fungi, and protozoa. Among the dinoflagellates, viral and bacterial associations were recognized a quarter century ago, yet their impact on host populations remains largely unresolved. By contrast, fungal and protozoan infections of dinoflagellates are well documented and generally viewed as playing major roles in host population dynamics. Our understanding of fungal parasites is largely based on studies for freshwater diatoms and dinoflagellates, although fungal infections are known for some marine phytoplankton. In freshwater systems, fungal chytrids have been linked to mass mortalities of host organisms, suppression or retardation of phytoplankton blooms, and selective effects on species composition leading to successional changes in plankton communities. Parasitic dinoflagellates of the genus Amoebophrya and the newly described Perkinsozoa, Parvilucifera infectans, are widely distributed in coastal waters of the world where they commonly infect photosynthetic and heterotrophic dinoflagellates. Recent work indicates that these parasites can have significant impacts on host physiology, behavior, and bloom dynamics. Thus, parasitism needs to be carefully considered in developing concepts about plankton dynamics and the flow of material in marine food webs.     

大亚湾澳头水域浮游植物群落结构及周年数量动态

对1997年至1998年广东省大亚湾澳头水域的浮游植物群落进行调查和分析。结果发现浮游植物65属198种;硅藻在种类组成和数量上都比甲藻占有优势,存在春季和秋季高峰,主要优势类群依次是角毛藻、骨条藻、拟菱形藻等;甲藻只存在春季高峰,代表种类有裸甲藻、原甲藻等。主要优势种类的生长与调查水域的盐度没有明显关系,但全年水温的季节性变化对优势种类的消长影响显著。Simpson多样性指数、Shannon-Weaver多样性指数、均匀度的年平均值分别是0.611、2.107、0.557,多样性指数没有明显的季节变化规律和水平分布规律。       

Seasonal phytoplankton responses to N:Si:P enrichment ratio in the Bizerte Lagoon (southwestern Mediterranean)

This study investigated the role of N, P and Si enrichments on phytoplankton in the Bizerte Lagoon (southwestern Mediterranean Sea, Tunisia) during March, June, August, October and December 2004. Polycarbonate bottles were enriched with different nutrients according to four treatments N:Si:P ratios [+NSi/-P (40:40:1), +P/-NSi (20:20:2,5), +NP/-Si (16:0:1) and +Si/-NP (16:32:1)] and incubated in situ during six days. Chl a and carbon biomass of phytoplankton varied significantly during the course of months, with the highest levels recorded in summer (4-4.4 microg Chl a L(-1) or 1126-1721 microg C L(-1)). Dinoflagellates dominated the initial phytoplankton communities, except in August, when diatoms represented a high fraction of microalgae (48%). Enrichment experiments induced significant increases in Chl a and in the final phytoplankton carbon biomasses. In summer (June/August), Si was the main limiting element for phytoplankton. Diatoms strongly responded to +Si/-NP and +NSi/-P enrichments and dominated the final phytoplankton communities (52-61%) in both treatments. Si played the most important role in the growth and development of diatoms. The biomasses and growth rates of dinoflagellates were significantly stimulated by +P/-NSi and +NP/-Si enrichments. After 6 days, dinoflagellates represented more than 70% of the total phytoplankton biomass in samples subjected to these treatments. Moreover, the addition of +P/-NSi increased the biomasses of several dinoflagellates. This suggests that dinoflagellates were mostly controlled by P availability. Unlike diatoms and dinoflagellates, flagellates showed weak responses to nutrient treatments during only some months of the year. The results showed that phytoplankton dynamics in the lagoon were influenced by nutrients in different manners.     

The structure and dynamics of phytoplankton assemblages from the inner part of the Thermaikos Gulf,Greece. I. Phytoplankton composition and biomass from May 1988 to April 1989

Qualitative and quantitative analyses of phytoplankton from the inner part of Thermaikos Gulf were carried out in the period May 1988–April 1989. A total of 154 taxa were identified in the phytoplankton. the monthly values of the phytoplankton biomass ranged between 614 and 6700 mg/m³ (wet weight). The seasonal development of the phytoplankton biomass exhibited three peaks. Diatoms, dinoflagellates and cryptophytes were the most important constituents of the gulf phytoplankton. Throughout the year, five different phytoplankton assemblages were distinguished.     

Influence of dissolved organic matter from terrestrial origin on the changes of dinoflagellate species composition in the Gulf of Riga,Baltic Sea

Hydrobiologia - A mesocosm experiment was used to investigate the effect of terrestrial-origin dissolved organic matter (DOM) on the development of dinoflagellates in natural summer phytoplankton...     

Taxonomy and palaeoecology of dinoflagellate cysts from Upper Oligocene freshwater sediments of Lake Enspel, Westerwald area, Germany

Freshwater dinoflagellates play an important role as primary producers in the lacustrine environment. A new species of dinoflagellates, Cleistosphaeridium lacustre, is described from Upper Oligocene sediments of palaeo-lake Enspel. They are associated with other phytoplankton, such as diatoms, chrysophytes, green algae and benthic cyanobacteria. Mass occurrences of this species are interpreted as algal blooms and may partly reflect seasonal successions. This phenomenon was controlled by volcanic activities in the depositional area, which led to an increase in nutrient supply.     

An ecosystem model of the phytoplankton competition in the East China Sea, as based on field experiments

An ecological dynamic model for the simulation of two pelagic phytoplankton groups is developed in this article. Model parameters were adjusted and validated based on the light-limited field culture experiments and the mesocosm experiments in the East China Sea (ECS). The calculation comparisons from the proposed model, along with field experiment observations, show that the model simulate the datasets very well, qualitatively and quantitatively. The parameters’ sensitivity analysis indicates that the competition between the diatoms and dinoflagellates is most sensitive to the photosynthetic process, followed by the exudation process of the phytoplankton, while the autolysis and respiration processes of phytoplankton and the grazing and exudation processes of zooplankton can also influence this competition to some extent. The sensitive parameters include: the photosynthetic optimal specific rate; the optimal irradiance and optimal temperature for phytoplankton growth; and the half-saturation constant for limiting nutrients, etc. Results of the sensitivity analysis also indicate that light, temperature and limiting nutrients are the controlling environmental factors for the competition between the diatoms and dinoflagellates in the ECS. In order to explore the effects of light and nutrients on the phytoplankton competition, simulations were carried out with varying light and nutrient conditions. Model simulations suggest that the diatoms favor higher irradiance, lower DIN/PO₄–P ratios, higher SiO₄–Si/DIN ratios and higher nutrient concentrations, as compared to the dinoflagellates. These results support the speculation that the increase in the DIN/PO₄−P ratio and the decrease in the SiO₄–Si/DIN ratio in the ECS may be responsible for the composition change in the functional Harmful Algal Bloom (HAB) groups from the diatom to the dinoflagellate communities over the last two decades. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: L. Naselli-Flores     

Changes in community structure and photosynthetic activities of total phytoplankton species during the growth,maintenance, and dissipation phases of a Prorocentrum donghaiense bloom

The potential interactions between the bloom-forming dinoflagellates and other phytoplankton during the algal bloom cycle are interesting, while the causes for the phytoplankton community changes were not fully understood. We hypothesized that phytoplankton community structure and photosynthetic activities of total phytoplankton have their special characteristics in different phases of the algal blooms. To test this hypothesis, a survey covering the process of a Prorocentrum donghaiense bloom in coastal waters between Dongtou and Nanji Islands was carried out from 9 to 20 May 2016, and the changes in the phytoplankton community and photosynthetic activities of total phytoplankton were determined. Surface seawater was sampled for microscopic analysis of phytoplankton composition and pulse amplitude modulated (PAM) chlorophyll fluorescence analysis of photosynthetic activities of the total phytoplankton species. A total of 25, 31, and 19 phytoplankton species were identified in its growth (9–12 May), maintenance (13–18 May) and dissipation phases (19–20 May), respectively. Diatoms were dominant in terms of species number while dinoflagellates were predominant at cell abundance. Dinoflagellates were the major dominant species during three phases of the bloom based on the dominance (Y) value, whereas the dominant species extended to dinoflagellates and diatoms including P. donghaiense, Coscinodiscus argus, Gonyaulax spinifera, Cyclotella sp. and Scrippsiella trochoidea in the dissipation phase. In the maintenance phase, the average cell abundances of the total phytoplankton and P. donghaiense were consistent with the chlorophyll a (Chla) concentration in the seawater; for the diversity indices of total phytoplankton species, Simpson index (C) was the highest while Shannon index (H′) and Pielou evenness index (J′) were the lowest. Furthermore, photosynthetic activities of the total phytoplankton species represented by the effective quantum yield (F_q'/F_m') and the maximum relative electron transport rate (rETR_max) in the maintenance phase were higher than those in the growth and dissipation phases. The results indicated that the characteristics of phytoplankton community structure and photosynthetic activities could be regarded as criteria in predicting the phases of algal blooms.     

Microphytoplankton of the Pitchavaram mangals,southeast coast of India: species composition and population density

Species richness of phytoplankton of the Pitchavaram mangals was high. There were 82 species constituted by 67 species of diatoms, 12 species of dinoflagellates and 3 species of bluegreen algae. The diatoms formed the bulk with 72% followed by the dinoflagellates with 15%, in which there were autochthonous (temporary and permanent) and allochthonous forms. Phytoplankton population density exhibited a wide seasonal fluctuation with the minimum during monsoon and the maximum during summer, suggesting the possible differential influence of various environmental factors.     

Study of phytoplankton characteristics in Tolo Harbour,Hong Kong,by HPLC analysis of chemotaxonomic pigments

Spatial and seasonal characteristics of phytoplankton in Tolo Harbour, Hong Kong, were studied by microscopic observation of phytoplankton samples and HPLC analysis of chemotaxonomic pigments. Diatoms dominated the phytoplankton. Common diatoms included Skeletonema costatum and species of Cerataulina, Leptocylindrus, Pseudo-nitzschia and Thalassiosira. Dinoflagellates occurred sporadically and mainly in the inner part of the harbour. The dinoflagellate Scrippsiella trochoidea was the causative organism for the red tide occurrences in March, April and September 2001. Significant positive correlations between fucoxanthin and diatoms and between peridinin and dinoflagellates suggested that fucoxanthin and peridinin were valuable chemotaxonomic markers for diatoms and dinoflagellates, respectively. Analysis of pigment ratios revealed that red tide events caused by dinoflagellates were marked by increase in the value of PERI:chl a and decrease in the value of FUCO:chl a. Increase in the value of FUCO:chl a also revealed the presence of a dense population of Pseudo-nitzschia that was not indicated by increase in chlorophyll a and fucoxanthin concentrations. Pigment analysis also revealed the presence of cyanobacteria, silicoflagellates, cryptophytes and green algae in the surface waters of Tolo Harbour.     

Microbial processes in a high-latitude fjord (Kongsfjorden, Svalbard): II. Ciliates and dinoflagellates

The composition and ecological role of ciliates and dinoflagellates were investigated at one station in Kongsfjorden, Svalbard, during six consecutive field campaigns between March and December 2006. Total ciliate and dinoflagellate abundance mirrored the seasonal progression of phytoplankton, peaking with 5.8 × 10⁴ cells l⁻¹ in April at an average chlorophyll a concentration of 10 μg l⁻¹. Dinoflagellates were more abundant than ciliates, dominated by small athecates. Among ciliates, aloricate oligotrichs dominated the assemblage. A large fraction (>60%) of ciliates and dinoflagellates contained chloroplasts in spring and summer. The biomass of the purely heterotrophic fraction of the ciliate and dinoflagellate community (protozooplankton) was with 14 μg C l⁻¹ highest in conjunction with the phytoplankton spring bloom in April. Growth experiments revealed similar specific growth rates for heterotrophic ciliates and dinoflagellates (<0–0.8 d⁻¹). Food availability may have controlled the protozooplankton assemblage in winter, while copepods may have exerted a strong control during the post-bloom period. Calculations of the potential grazing rates of the protozooplankton indicated its ability to control or heavily impact the phytoplankton stocks at most times. The results show that ciliates and dinoflagellates were an important component of the pelagic food web in Kongsfjorden and need to be taken into account when discussing the fate of phytoplankton and biogeochemical cycling in Arctic marine ecosystems.     

The phytoplankton of Great Bitter Lake,Egypt, including the impacts of nutrient-laden and heated effluents

A year-long survey of the phytoplankton and nutrients in Great Bitter Lake indicates that this is a severely eutrophic lake. Chlorophyll levels were consistently high (>30μg/l), especially in summer (>90μg/l). The phytoplankton community comprised mostly diatoms and blue-green algae, although dinoflagellates and green algae were important at times. Local effects of effluent from a drain coming from the city of Ismailia were evident, although the effect of tourist hotels at Palma Beach was not detectable. The discharge of heated water from a thermal power plant raised the water temperature in the impacted area by 13°C in autumn and 22°C in summer and also caused decreases in chlorophyll and phytoplankton abundance. Dissolved nutrient levels were high and, especially at the offshore station, had a rather constant ratio of dissolved inorganic nitrogen to phosphate. The distribution of phytoplankton and chlorophyll were related more to temporal, presumably seasonal, variation than proximity to point sources of pollution.     

Temporal and spatial dynamics of phytoplankton diversity in the East China Sea near Jeju Island (Korea): A pyrosequencing-based study

The East China Sea (ECS) has long been considered an important monitoring site for oceanic ecosystem changes because many water currents and river discharges constantly influence this area. In this study, the community structure and diversity of phytoplankton in the northern part of the ECS adjacent to Jeju Island were explored using small subunit ribosomal RNA (SSU) pyrosequencing. We analysed samples collected from four stations from the surface and at 30-m and 50-m depths during April and September 2011. We observed spatial and temporal variations in the phytoplankton community. Among phytoplankton, diatoms and dinoflagellates constituted a major portion at all stations (60–90%). However, comparison of the April and September samples showed seasonal variation and shifts in the dispersion of diatom and dinoflagellates among stations. Among stations, diatoms dominated St. 1 and others were dominated by dinoflagellates. Furthermore, phylotypes of potentially toxin-producing genera such as Karlodinium, Heterocapsa, Gymnodinium, Gyrodinium, and Pseudo-nitzschia were dominant in this area.     

Variation of Phytoplankton in a Tropical Estuary (Vellar Estuary,Bay of Bengal,India)

The phytoplankton species composition and community structure were studied at two stations in the Vellar estuary from January to December, 1983. A total of 117 species of phytoplankton belonging to various groups, namely diatoms (90), dinoflagellates (21), Chlorophyceae (3), Cyanophyceae (2) and silicoflagellates (1) were observed during the study. The species diversity, richness and evenness values varied from 0.7 to 4.2 units/individual, 0.9 to 5.7 and 0.19 to 0.75 respectively. Dominance index values varied between 32.6 and 96.4 during the study period.     

Species of dinoflagellates of the genus Gambierdiscus (Dinophyceae) in the Mexican Caribbean Sea

Some dinoflagellates with benthic habits are related to ciguatera intoxication by fish consumption, especially in tropical areas. In the Mexican Caribbean, ciguatera is relatively common, but only one paper seems to have been published on the subject, and there are very few publicactions on phytoplankton and benthic microalgae. Material collected along the coast of the State of Quintana Roo with phytoplankton net (54 mm) and directly from sediment and epiphytes of macroscopic plants, was searched for toxic and other associated dinoflagellates. Samples were studied by light and scanning electron microscopy. Morphological characters were useful for species identification, but eventually physiological, ecological and molecular characters could also be used. Three species of Gambierdiscus, related to the production of ciguatera toxins, were identified: G. belizeanus, G. toxicus and G. yasumotoi. They are distributed in shallow coastal areas, including coastal lagoons.     

Phytoplankton in the surface and chlorophyll maximum off southern California in August, 1978

A synoptic sampling of 30 stations in a 25 km x40 km grid closeto the southern California coast revealed that chlorophyll andphytoplankton biomass were higher nearshore and to the south,where relatively large dinoflagellates dominated. A subsurfacechlorophyll maximum was present at each station, near the nitraclineand 10% light level. Nearshore and to the south, these maximarepresented higher levels of phytoplankton biomass than at thesurface whereas at the other stations, chlorophyll maxima couldbe attributed to physiological changes in chlorophyll contentof small flagellated phytoplankton rather than to the accumulationof phytoplankton at depth. Univariate and multivariate statisticalprocedures were used to demonstrate that phytoplankton assemblagesseparated by tens of meters in the vertical were just as differentas those separated by tens of kilometers in the horizontal.We conclude that residence time of water near the coast is ofgreat importance to the determination of the abundance and taxonomiccharacteristics of phytoplankton, and that advection of offshorewater towards the coast was the major determinant of the patternobserved during our study. ¹Present address: University of Texas, Port Aransas Marine Laboratory,Port Aransas, TX 78373, USA     

河北张家口下花园地区新元古代下马岭组油页岩中的红藻化石

通过对下花园地区晚前寒武纪下马岭组油页岩的研究,发现了保存极为完好的红藻化石,同时也发现特定的底栖宏观红藻可以作为重要生烃母质,在中—低成熟度条件下,甚至可以成为重要生油母质。     

The Ecological Roles of Heterotrophic Dinoflagellates in Marine Planktonic Community1

Heterotrophic dinoflagellates are ubiquitous and often abundant protists in marine environments. Recently, several novel predator-prey relationships between heterotrophic dinoflagellates and other planktonic organisms have been discovered and shown to have diverse ecological roles. Heterotrophic dinoflagellates are predators on a wide array of prey items, including phytoplankton, copepod eggs, and early naupliar stages. They are in turn important prey for some metazoa. Some heterotrophic dinoflagellates are predators of and simultaneously prey for other dinoflagellates. These newly discovered predator-prey relationships may influence our conventional view of energy flow and carbon cycling in the marine planktonic community.