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。       

Relationship between propagule pressure and colonization pressure in invasion ecology: a test with ships' ballast

Increasing empirical evidence indicates the number of released individuals (i.e. propagule pressure) and number of released species (i.e. colonization pressure) are key determinants of the number of species that successfully invade new habitats. In view of these relationships, and the possibility that ships transport whole communities of organisms, we collected 333 ballast water and sediment samples to investigate the relationship between propagule and colonization pressure for a variety of diverse taxonomic groups (diatoms, dinoflagellates and invertebrates). We also reviewed the scientific literature to compare the number of species transported by ships to those reported in nature. Here, we show that even though ships transport nearly entire local communities, a strong relationship between propagule and colonization pressure exists only for dinoflagellates. Our study provides evidence that colonization pressure of invertebrates and diatoms may fluctuate widely irrespective of propagule pressure. We suggest that the lack of correspondence is explained by reduced uptake of invertebrates into the transport vector and the sensitivity of invertebrates and diatoms to selective pressures during transportation. Selection during transportation is initially evident through decreases in propagule pressure, followed by decreased colonization pressure in the most sensitive taxa.     

Downwelling and dominance of autochthonous dinoflagellates in the NW Iberian margin: The example of the Ría de Vigo

Dinoflagellate blooms in coastal upwelling systems are restricted to times and places with reduced exchange and mixing. The Rías Baixas of Galicia are four bays in the NW Iberian upwelling with these characteristics where harmful algal blooms (HABs) of dinoflagellates are common. These blooms are especially recurrent at the end of the upwelling season, when autumn downwelling amplifies accumulation and retention through the development of a convergence front in the interior of Rías. Because oceanic water enters the Rías during downwelling, it has been hypothesised that dinoflagellate blooms originate by the advection and subsequent accumulation of allochthonous populations. To examine this possibility, we studied the microplankton succession in relation to hydrographic variability in the Ría de Vigo (one of these four bays) along an annual cycle making use of a high sampling frequency. The results indicated that upwelling lasted from May to August, with downwelling prevailing in winter. Microplankton during upwelling, although dominated by diatoms, evidenced a progressive increase in the importance of dinoflagellates, which achieved maximum abundance at the end of the upwelling season. Thus, diatoms characterised the spring bloom, while diatoms and autochthonous dinoflagellates composed the autumn bloom. Diatoms dominated during the first moments of the autumn downwelling and dinoflagellates were more abundant later, after stronger downwelling removed diatoms from the water column. Since the dinoflagellates selected by downwelling belonged to the local community, it is concluded that advection of alien populations is not required to explain these autumn blooms.     

Simulating motile algae using a mixed Eulerian-Lagrangian approach: does motility promote dinoflagellate persistence or co-existence with diatoms?

Dinoflagellates are characterized by low maximum photosynthetic rates and high respiratory costs. Recent evidence also suggests that dinoflagellates are disproportionately abundant in the diets of many copepods. This suggests that at least some species are preferred prey types. This begs the question: 'How do dinoflagellates co-exist with other, seemingly competitively superior, algal taxa'? Their motility may enable them to maintain position better in the light-rich surface waters, and more successfully make the return journey into deeper waters in order to replenish their internal nutrient stores when surface nutrients become depleted. This theory is examined using a depth-resolved model of algal dynamics. Nutrients and organic detrital matter are represented on a Eulerian grid, whilst a Lagrangian approach is used to represent dinoflagellates and diatoms. The model indicates that strictly autotrophic dinoflagellates have difficulty balancing their metabolic budgets. Even in the absence of competition from diatoms, motility is almost essential to dinoflagellate persistence. Only extremely motile dinoflagellates are able to compete successfully with diatoms. In reality, an increasing number of dinoflagellate species are being found to be mixotrophic. This model suggests that mixotrophy may often be an obligatory, rather than optional, behaviour.      

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.     

Diel feeding pattern and prey selection of mesozooplankton on microplankton community

Mesozooplankton play an important role in transporting energy from microphytoplankton and microzooplankton to higher trophic levels. However there were few studies on the diel feeding patterns and prey selectivity of mesozooplankton. We conducted feeding experiments of mesozooplankton in the East China Sea to determine their respective diel feeding patterns on diatoms, ciliates and dinoflagellates, and to assess the contribution of these prey items to mesozooplankton diet. The results showed higher mesozooplankton grazing rates on ciliates and dinoflagellates than on diatoms at the day time, and the opposite pattern at the night time. A significant prey selection was observed, in which mesozooplankton positively selected ciliates and dinoflagellates during day and diatoms at night. The different grazing reactions of mesozooplankton toward each prey item might be related to the mobility of the prey. In all, microzooplankton (ciliates and dinoflagellates) provided the majority of the mesozooplankton carbon ingestion, even at a station dominated by small pennate diatoms. In particular, dinoflagellates are an important prey of mesozooplankton in the East China Sea and their contribution to the diet of mesozooplankton is unproportionate to their abundance.     

Carbon:chlorophyll <Emphasis Type="Italic">a</Emphasis> ratio,assimilation numbers and turnover times of Lake Kinneret phytoplankton

Carbon to chlorophyll a (C:Chl) ratios, assimilation numbers (A.N.) and turnover times of natural populations of individual species and taxonomic groups were extracted from a long-term database of phytoplankton wet-weight biomass, chlorophyll a concentrations, and primary production in Lake Kinneret, Israel. From a database spanning more than a decade, we selected data for samples dominated by a single species or taxonomic group. The overall average of C:Chl was highest for cyanophytes and lowest for diatoms, while chlorophytes and dinoflagellates showed intermediate values. When converting chlorophyll a to algal cellular carbon this variability should be taken into account. The variability in C:Chl within each phylum and species (when data were available) was high and the variability at any particular sampling date tended to be greater than the temporal variability. The average chlorophyll a-normalized rate of photosynthetic activity of cyanophytes was higher and that of the dinoflagellates lower than that of other phyla. Turnover time of phytoplankton, calculated using primary productivity data at the depth of maximal photosynthetic rate, was longest in dinoflagellates and shortest in cyanophytes, with diatoms and chlorophytes showing intermediate values. The more extreme C:Chl and turnover times of dinoflagellates and cyanobacteria in comparison with chlorophytes and diatoms should be taken into consideration when employed in ecological modeling.     

Structure of the summer under fast ice microbial community near Syowa Station,eastern Antarctica

Temporal variations in the microbial community structure of plankton, which is composed of autotrophic and heterotrophic pico-, nano- and microplankton, were investigated during the austral summer of 2005/2006 under fast ice near Syowa Station, eastern Antarctica. Autotrophic algal populations were composed almost entirely of diatoms followed by phytoflagellates such as autotrophic dinoflagellates and cryptophytes. Among the microbial community, heterotrophic biomass was dominated by heterotrophic dinoflagellates and naked ciliates and finally exceeded autotrophic biomass. Qualitative microscopic analysis revealed that heterotrophic dinoflagellates were ingesting large number of diatoms. Synchronizing fluctuation of naked ciliates with phytoflagellates suggested a predator–prey relationship between them. Our results suggest that the pelagic food webs under the extensive ice-covered areas in coastal Antarctic regions are not short but complex.     

Seasonal variations of diatoms and dinoflagellates in a shallow,temperate estuary,with emphasis on neritic assemblages

Seasonal changes in the diatom and dinoflagellate assemblages were examined in the neritic zone of the Urdaibai estuary (north Spain) with regard to some major physical and chemical variables during an annual cycle. A total of 81 diatoms and 38 dinoflagellates were identified and quantified during the study period. Both groups displayed a distinctive pattern of seasonal succession. The seasonal distribution of the Shannon index showed a trend of increasing values from the upper estuary to the lower neritic segment. The diatom diversity maxima were observed in February, April and September, and dinoflagellate maxima in April–May, July and October. Diatoms dominated the assemblages, reaching 1×10⁶ cells l^–1 from April to September. A shift from large diatoms and dinoflagellates to small bloom-forming taxa was observed during winter–early spring. A spring diatom bloom composed of Rhizosolenia spp. was observed in April, while small chain-forming taxa (chiefly Chaetoceros spp.) dominated from June to September. Cell maxima for both groups in late summer were produced by the diatoms Chaetoceros salsugineum and Skeletonema costatum, and by the dinoflagellates Heterocapsa pygmaea and Peridinium quinquecorne. Silicate availability by river supply and strong tidal-mixing of the water column seem to determine the year-round dominance of diatoms over dinoflagellates.     

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.     

Quantification of diatom and dinoflagellate biomasses in coastal marine seawater samples by real-time PCR

Two real-time PCR assays targeting the small-subunit (SSU) ribosomal DNA (rDNA) were designed to assess the proportional biomass of diatoms and dinoflagellates in marine coastal water. The reverse primer for the diatom assay was designed to be class specific, and the dinoflagellate-specific reverse primer was obtained from the literature. For both targets, we used universal eukaryotic SSU rDNA forward primers. Specificity was confirmed by using a BLAST search and by amplification of cultures of various phytoplankton taxa. Reaction conditions were optimized for each primer set with linearized plasmids from cloned SSU rDNA fragments. The number of SSU rDNA copies per cell was estimated for six species of diatoms and nine species of dinoflagellates; these were significantly correlated to the biovolumes of the cells. Nineteen field samples were collected along the Swedish west coast and subjected to the two real-time PCR assays. The linear regression of the proportion of SSU rDNA copies of dinoflagellate and diatom origin versus the proportion of dinoflagellate and diatom biovolumes or biomass per liter was significant. For diatoms, linear regression of the number of SSU rDNA copies versus biovolume or biomass per liter was significant, but no such significant correlation was detected in the field samples for dinoflagellates. The method described will be useful for estimating the proportion of dinoflagellate versus diatom biovolume or biomass and the absolute diatom biovolume or biomass in various aquatic disciplines.     

THE OCCURRENCE OF CHLOROPHYLL C1 AND C2 IN ALGAE1

Forty-two species of chlorophyll c-containing algae (diatoms, dinoflagellates, chrysomonads, haptophytes, cryptomonads and xanthophytes) were examined for their content of chlorophyll c₁ and c₂. This work, and recent studies on c₁/c₂ distribution in the literature (total 86 species), show that chlorophyll c₂ is universal to all algae examined. Chlorophyll c₁ occurs in addition to c₂ in brown seaweeds, diatoms, chrysomonads, haptophytes (coccolithophorids) xanthophytes and the, fucoxanthin-containing dinoflagellates; c₂ only occurs in dinoflagellates and cryptomonads. Two exceptions to the generalizations are one dinoflagellate and one cryptomonad containing c₁ in addition to c₂ No explanation can be offered on present knowledge for these exceptions. No alga was found containing only chlorophyll c₁. Chlorophyll c, far from being a minor accessory chlorophyll, occurred in amounts almost equal to chlorophyll a(some diatoms and dinoflagellates) or ranged from 50 to 20% of the chlorophyll a (diatoms, dinoflagellates, chrysomonads, cryptomonads, browns). Xanthophytes, however, contained only trace amounts of chlorophyll c with ratios of chlorophyll a:c ranging from 55:1 to 116:1 on a weight basis. In those algae with both chlorophyll c components, c₁ and c₂, occurred either in equal amounts, or chlorophyll c₂was twice the c₁ content.     

Effects of UV-B radiation on growth and motility of four phytoplankton species

A depletion of the stratospheric ozone layer would result in an increased UV-B radiation, which could have harmful effects on marine organisms. The aim of this study was to determine the effects of an enhanced UV-B radiation (280–320 nin) on the motility and growth in four Swedish phytoplanklon species. The different plankton species were exposed to different doses of UV-B radiation during growth. The growth of the motile dinoflagellates, Gyronidium aureolum Hulburt (Ba 6), and Prorocentrum minimum (Pav.) P. Schiller (Ba 12), was more sensitive to UV-B radiation than the non-motile diatoms Dityhim brightwellii (P. West) Grun (Ba 15) and Phaeodactylum tricornutum Bohlin (Ba 16). One week of UV-B radiation 2 h daily (159 J m⁻² day⁻¹), had a dramatic effect on the growth of the dinoflagellates, while the diatoms were nearly unaffected. On the other hand, when given higher intensity of UV-B radiation (312, 468 and 624 J m⁻² day⁻¹) during the initial phase of growth, also the growth of the diatom, D. brightwellii, was inhibited. Not only the growth but also the swimming speed of the dinoflagellates C. aureolum and P. minimum were affected by UV-B radiation. The speed decreased rapidly after 1–2 h of UV-B radiation (312 J m⁻² day⁻¹), and after longer irradiation times the dinoflagellates lost their motility. G. aureolum exposed to UV-B radiation, regained normal speed after two weeks of visible light.     

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.     

THECATE HETEROPHIC DINOFLAGELLATES: FEEDING BEHAVIOR AND MECHANISMS1

The feeding of 18 species of thrcale hetrophi dinoflagellates from three genera (Protoperidininm, Oblea, Zygabikodinium) can all be described within one general framework. These species engulf diatoms and other prey with a pseudopod (herein terned a “Pallium”)which originates at the flagellar pore in the sulcus. The pallium is a highly plastic, membranous organ which rasily strethes to accommodate spines and many as 58 diatom cells in a chain. The contents of the phytoplanklon prey are liquified and transporued throughthe pallioum typically within 7 to 30 minutes of capture (although feeding may last 2 h) teaving an intact but empty cell wall or frustule. Thus far, with few exceptions, Protoperidinium specises have been observed feeding inly on diatoms, whereas two diplopsaloid species feed on dinoflagellates and prasinophytes as well. In four species from the three genera studied. a capture filament has been observed that connects the food to the dinoflagellate prior to extension of the pallium, sometimes allowing the cell to pull the food while swimming. A distinctive precapture swimming behavior is also deseribed foe six species, suggesting that the dinoflagellates are selective grazers.     

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.     

Structure of the phytoplankton communities in two lagoons of different salinity in the Sfax saltern (Tunisia)

The structure and ecophysiological characteristics of phytoplanktonassemblages were studied for 10 months in two lagoons of differentsalinity (40 and 90) in the saltern of Sfax (Tunisia), in relationto environmental factors. These assemblages were largely dominatedby diatoms and dinoflagellates, which accounted for >90%of total abundance. A principal components analysis clearlydifferentiated the observations made in the two lagoons, thedominant correlate being the salinity. Euryhaline species andparticularly diatoms developed preferentially in the less salinelagoon, and were largely replaced by stenohaline species representedby dinoflagellates, which were dominant in the more saline lagoon.Calculation of the pigment diversity index and the species diversityindex showed that the phytoplankton assemblages studied werepermanently in a juvenile stage, as the species restructuringrelated to environmental constraints did not allow them to reachthe climax stage at any given time in their development. Despitethe heavy constraint imposed by the salinity, it is evidentthat other environmental factors, e.g. temperature, play a rolein the regulation of the planktonic communities. Finally, thedifference in the size distribution of the total microbial biomass,estimated by the assay of particulate proteins, showed thatthere was a significant change in the community structure andthe planktonic trophic networks, in parallel with the increasein salinity.     

The characteristics and transparent exopolymer particle (TEP) content of marine snow formed from thecate dinoflagellates

Abundant marine snow containing diatoms and detritus, but dominatedby large, bioluminescent thecate dinoflagellates and their temporaryvegetative cysts, especially several species of the genus Gonyoulax,was observed at six stations in the Santa Barbara Channel, California,in 1989 and 1994. These aggregates were unusually cohesive andmucus rich, and contained 2–4 times more mass, particulateorganic carbon (POC), particulate organic nitrogen (PON) andchlorophyll a per unit aggregate volume than more common typesof marine snow formed from diatoms, fecal matter, larvaceanhouses or miscellaneous detritus. However, the relationshipbetween aggregate size and the concentration of TEP (transparentexopolymer particles which form the mucus matrix of most marinesnow) was similar to that of other types of aggregates, suggestingthat much of the copious gel-like material within dinoflagellateaggregates was not TEP. While this is the first report of abundantthecate dinoflagellates occurring within large, rapidly sinkingmarine aggregates, the data do not support the conclusion thatmass aggregation and subsequent sedimentation of blooms is partof the life history adaptations of thecate dinoflagellates,as it is for some diatoms. The high abundance of free-livingdinoflagellate cells and temporary cysts, and the similar proportionof dinoflagellates relative to other algal and chemical componentsin both aggregates and the surrounding seawater, indicate thatthe dinoflagellates were not differentially aggregating. Evenso, passive accumulation of dinoflagellates in marine snow throughaggregation processes may result in more rapid transport ofdinoflagellate-generated material to the deep ocean, alter thenature of sinking particulate matter following dinoflagellateblooms, and increase the nutritional value of marine snow asa food source for zooplankton and fish.     

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.     

Nutritive Value and Selection of Food Particles by Copepods During a Spring Bloom of Phaeocystis sp. in the English Channel, as Determined by Pigment and Fatty Acid Analyses

In this study phytoplankton pigments and fatty acids were usedas biomarkers to study trophic relationships between phytoplanktonand zooplankton. These markers permit the characterization ofboth suspended matter and copepods, allowing examination ofthe transfers from food to zooplankton. A drogue study was carriedout to follow a water mass in the coastal waters off the easternEnglish Channel over a 3-day period, with samples collectedevery 3 h. The study focused on the dominant calanoid copepodspecies: Temora longicornis, Acartia clausi and Pseudocalanuselongatus. Our study was performed during the spring phytoplanktonbloom when solitary cells of Phaeocystis sp. formed 90% of thetotal phytoplankton. Fatty acid analyses provided an indicationof the low nutritive value of these algal cells; in contrastto other algal species which had higher nutritional value (e.g.colony-forming diatoms, Cryptophytes and dinoflagellates). Ourresults suggest that all species selectively grazed on Phaeocystissp. and non-selectively on diatoms. Dinoflagellates were avoidedby all species. Temora longicornis selectively grazed on Cryptophytes,which may be related to the nutritional value of this algae.The fatty acid composition of the three copepod species indicatedan ‘herbivorous’ diet for P.elongatus and an omnivorousone for A. clausi and T. longicornis, which is less opportunist.