福建敖江口表层沉积硅藻空间分布特征

为探讨福建敖江口表层沉积硅藻空间分布特征,2019年7月对敖江口进行表层沉积硅藻的采样调查,并研究了硅藻与环境因子的关系。结果表明,从13个站点共检出硅藻114种,隶属于39属。硅藻丰度具有从河口向外海先减少后增加的变化特征。聚类分析表明,主要硅藻属种可划分为淡水种组合带和半咸水-咸水种组合带。典型对应分析（CCA）表明,表层海水温度和盐度是影响硅藻分布的主要环境变量。河口区盐度相对较低,主要分布淡水种双面曲壳藻、优美曲壳藻和颗粒沟链藻;外海区北部盐度相对较高,主要分布咸水种流水双菱藻;外海区南部盐度相对较低,主要分布淡水种优美曲壳藻和颗粒沟链藻;滩涂的沉积物较粗,主要分布优美曲壳藻。此外,河口区和外海区南部可能存在一定的水体污染。     

Algal communities of a geothermally heated lagoon on Deception Island (South Shetland Islands)

Kroner Lake, located at Deception Island (Maritime Antarctica), is a unique geothermally heated lagoon in Antarctica. It is declared as special site of scientific interest (SSSI) by Scientific Committee for Antarctic Research (SCAR) for its high biodiversity. A sharp environmental heterogeneity is registered in this lagoon, due to its connection to the sea in its southern margin, and to the input of warm freshwater in the northern one (because of hot springs). This study analyses the biodiversity and abundance of the algal communities (phytoplankton and benthic assemblages) and their relationship with environmental factors. In particular, strong spatial differences of both temperature and conductivity were recorded. The biological studies revealed that the phytoplankton (nanoplankton and microplankton) was dominated by marine diatom species, while the pico-sized fraction was composed by Cyanobacteria Synechococcus-like cells. The epipelon was mainly represented by chain and tubicolous diatoms, among which, Melosira nummuloides was one of the most abundant species. Filamentous Cyanobacteria were also frequently recorded in the algal mats. Kroner Lake is subject to a strong marine influence. Phytoplankton is absolutely dominated by marine diatoms. Spatial variations in temperature and conductivity recorded in the lagoon influence the distribution of the aquatic communities. The greater abundance of pico-sized cells coincided with the warmest site of the water body. Regarding the benthic community, the contribution of freshwater and brackish species is comparatively more important than for the phytoplankton, although the high contribution of marine-derived algae was also evident.     

Diatom assemblages in tsunami deposits associated with the 2004 Indian Ocean tsunami at Phra Thong Island, Thailand

Diatom assemblages in sandy deposits of the 2004 tsunami at Phra Thong Island, Thailand may provide clues to flow conditions during the tsunami. The tsunami deposits contain one or more beds that fine upward, commonly from medium sand to silty very fine sand. Diatom assemblages of the lowermost portion of the deposit predominantly comprise unbroken beach and subtidal species that live attached to sand grains. The dominant taxa shift to marine plankton species in the middle of the bed and to a mix of freshwater, brackish, and marine species near the top. These trends are consistent with expected changes in current velocities of tsunami through time. During high current velocities, medium sand is deposited; only beach and subtidal benthic diatoms attached to sediment can be incorporated into the tsunami deposit. High shear velocity keeps finer material, including planktonic diatoms in suspension. With decreasing current velocities, finer material including marine plankton can be deposited. Finally, during the lull between tsunami waves, the entrained freshwater, brackish, and marine species settle out with mud and plant trash. Low numbers of broken diatoms in the lower medium sand implies rapid entrainment and deposition, whilst selective breakage of marine plankton (Thalassionema nitzschioides, and Thalassiosira and Coscinodiscus spp.) in the middle portion of the deposit probably results from abrasion in the turbulent current before deposition.     

The Development of Vertical Migration Patterns in the Sediments of Estuaries as a Strategy for Algae to Resist Drift with Tidal Currents

The phenomenon of massive algae migrations to the surface of mud flats at low tide was quantitatively investigated. Differences were noted in the behavior of the individual species. This adaptation to the tidal rhythm is obviously effective for preventing the algae from drifting to the sea, and its development can shed much light on the natural history of the species involved. Euglena obtusa and Caloneis amphisbaena var. subsalina apparently arose by a natural selection process among ancestors from lentic freshwater bodies, while Navicula salinarum, Cylindrotheca signata, and several other diatoms probably invaded the freshwater habitat from marine mud flats, where they were preadapted to the tides.     

pH and Eh on Aldabra atoll 1. comparison of marine and reshwater environments

An account is given of the range of pH and Eh in marine and freshwater aquatic sites on one atoll (Aldabra, Indian Ocean). There is a very wide range in values of pH and Eh for both marine and freshwater environments, the range for pH in general being wider in freshwater ones and Eh in marine ones. Photosynthetic microbial communities on lagoon sediments may be arranged in an approximate order of their association with sediments of particular Eh values. These are, from high to low: Scytonema sp., pennate diatoms, Schizothrix sp., Microcoleus chthonoplastes, Hyella balani, purple phototrophic bacteria.     

A multiproxy approach to inferring Holocene paleobotanical changes linked to sea-level variation,paleosalinity levels,and shallow lake alternative states in Negra Lagoon,SE Uruguay

A multiproxy analysis of diatoms, chrysophyte cysts, opal phytoliths, and palynomorphs was undertaken in Negra Lagoon, to decipher Holocene changes in paleobotanical proxies associated with sea-level changes and paleolimnological conditions. Before the Holocene transgression (7000 yr BP), a terrestrial system was inferred as no aquatic palynomorphs or biogenic silica remains were recorded. During the sea-level maximum (5200 yr BP), marine/brackish conditions were established as indicated by diatoms, Chenopodiaceae, and a high content of cysts of Peridinioideae. The catchment consisted of grasslands and wetlands as indicated by the opal phytolith data. The Holocene transgression was followed by a sea-level decrease, which led to the onset of brackish/freshwater conditions as inferred from the co-dominance of freshwater and marine/brackish diatoms. This is also supported not only by the concomitant increase in non-siliceous freshwater microalgae and emergent macrophytes, but also by the presence of Myriophyllum. As sea level continued to decrease during late Holocene, a freshwater system was observed because of the complete separation from the ocean. Chrysophyte cysts were consistently recorded and brackish diatoms exhibited reduced abundances. The observed limnological changes are consistent with the alternative states hypothesis of Scheffer’s model (1998). That is, the clear water phases were explained because of high macrophyte abundances, low phytoplankton frequencies, high cyst to diatom ratios, and increase in frequencies of benthic diatom species. Conversely, turbid phases were likely to occur when low cyst to diatom ratios together with increase in planktonic diatoms and decrease in macrophytes values were detected. This highlights the importance of this approach to detect long-term changes in shallow lake alternative states.     

PHYLOGENETIC ANALYSIS OF THE MARINE AND FRESHWATER THALAS-SIOSIROID DIATOMS

The thalassiosiroid centric diatoms are distinguished by at least one synapomorphy, the strutted process or fultoportula. Variously classified as a family (Thalassiosiraceae) or an order (Thalassiosirales) among centric diatoms, it is generally conceded that the group of several hundred fossil and living species is monophyletic as a whole. There are two ecological groups of thalassiosiroids, marine and freshwater. It has been hypothesized, based on an ecletic, non-rigorous, evolutionary taxonomy perspective that both the marine and freshwater ecological groups are also monophyletic, but this hypothesis has never been tested in a rigorous framework. Likewise, the freshwater thalassiosiroid species have been grouped into several genera and subgenera using an evolutionary taxonomic approach, but these hypotheses have not fully been tested using cladistic analysis. Focusing mainly on freshwater species, but including at least one representative of each marine genus and one representative from each of several proposed subgeneric groupings of the genus Thalassiosira , we scored morphological characters for fossil and living marine and freshwater Thalassiosiraceae to test these hypotheses. Our cladistic results provide strong support for monophyly for the freshwater group, but it seems unlikely that the marine group is monophyletic. The cladistic results are corroborated to greater or lesser degrees by the fossil record. The implications for evolution in the group and for taxon sampling in molecular studies we are conducting will be discussed.     

VITAMIN B12-BINDER AND OTHER ALGAL INHIBITORS1

Euglena gracilis Klebs, Poterioochromonas malhamensis (Pringsheim) Peterfi, Monochrysis lutheri Droop, Isochrysis galbana Parke and Phaeodactylum tricornutum Bohlin are known to release into the medium a substance which binds free vitamin B₁₂. The binder, apparently a glycoprotein, makes vitamin B₁₂ unavailable and inhibits growth of vitamin B₁₂-requiring microorganisms. Culture filtrates of selected marine diatoms, chrysophytes, cryptophytes, dinoflagellates and green algae contained the binder, indicating that binder release was not restricted to any algal group. However the three prokaryotic bluegreens tested do not produce B₁₂-binder. Production is also independent of the nutritional requirements of the donor, being produced by autotrophs and auxotrophs. The binders produced by these marine species have similar properties: they are heat labile; inhibition is not species-specific; it is competitive, being reversed by adding B₁₂. Production increases with density of the culture and is not restricted to stationary or scenescent cells. The marine species tested produced much less B₁₂ than the freshwater Euglena and Poterioochromonas; the inhibition is reversed by 20–50 ng · 1^?1 of B₁₂ for marine species which reach moderate densities and by 150–300 ng · 1^?1 B₁₂ for the densely growing species. Consequently the binder may affect the growth of B₁₂-requiring species only in environments like the open ocean poor in B₁₂. By contrast, the marine algae produce other inhibitors which are often heat stable and very inhibitory. These inhibitors, being species-specific and less labile, may be more important in affecting the succession of algal species in natural waters.     

Presence of free D-amino acids in microalgae

Several species of microalgae (phytoplankton), 4 species of freshwater algae and 4 species of marine diatoms, were cultured germ-free in the laboratory. The presence of free D-amino acids was verified in these species by a reversed-phase HPLC analysis. D-Aspartate was detected in all the microalgae examined, but D-alanine was only present in the marine diatoms. The D-amino acid content in Asterionella sp. of the marine diatoms increased from the exponential phase to the stationary phase and then decreased to the phase of decline.     

GROWTH INHIBITION AND TOXICITY OF THE DIATOM ALDEHYDE 2‐TRANS, 4‐TRANS‐DECADIENAL ON THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYCEAE)1

A common aldehyde present in marine and freshwater diatoms, 2‐trans, 4‐trans‐decadienal (A3), is involved in the wound‐activated response of diatoms to copepod grazing. Upon breakage of the diatom cell membrane, aldehydes are enzymatically produced by the rapid conversion of precursors and strongly impact copepod reproduction by impairing egg production and hatching success, inducing teratogenic embryos modifications. In this study, A3 was assayed with the marine diatom Thalassiosira weissflogii (Grunow) Fryxell et Hasle. The aldehyde concentration necessary to reduce 50% growth rate (EC₅₀) was 0.29 mg·L^?1. Decadienal was found to inhibit T. weissflogii cell growth in a dose‐ and time‐dependent manner, with irreversible effects after 24 h of exposure. Decadienal induced a degenerative process, through modifications of cell membrane characteristics, interference with cell cycle progression, and with cell metabolic activity, leading to cell death. A preferential action of A3 on dividing cells was observed. Photosynthetic efficiency significantly decreased upon exposure to the aldehyde, paralleled by an increase in diatoxanthin, suggesting a protective role of this xanthophyll, usually involved in photoprotection. Dying cells exhibited the morphological and biochemical features that bear close resemblance to apoptosis of mammalian cells, including cell shrinkage, chromatin condensation, and degradation of nuclear DNA to nucleosomal size fragments. These data are the first direct evidence to show aldehydes are toxic to diatoms. We suggest a possible nontoxic role of such compounds as chemical signals of unfavorable conditions within the phytoplankton communities, which may be relevant for the population dynamics of diatoms during blooms.     

Associating particulate essential fatty acids of the ω3 family with phytoplankton species composition in a Siberian reservoir

1. We studied variation in the composition of fatty acids in the seston of a small freshwater reservoir with changes in phytoplankton composition during four growth seasons. We focused on the dynamics of the ω3 fatty acids because of their potential importance for zooplankton nutrition. 2. Total diatoms were related to the 20:5ω3 fatty acid (eicosapentaenoic, EPA) content in seston. Among two dominant diatom genera, Cyclotella was not associated with EPA content. In contrast, there was a significant correlation between Stephanodiscus and the percentage contribution and content of EPA throughout the study. Hence, freshwater diatoms can differ strongly in content of the essential EPA. 3. We considered abundant cyanobacteria as a potential source of 18:3ω3 fatty acid (linolenic, ALA) to aquatic food webs. Among four dominant cyanobacteria species, two (Anabaena flos‐aquae and Planktothrix agardhii) showed significant correlation with the ALA content of the seston, while the other two (Aphanizomenon flos‐aquae and Microcystis aeruginosa) did not. 4. Dinophyta had a relatively high level of 22:6ω3 (docosahexaenoic, DHA) for freshwater species and can be also a source of EPA to aquatic food webs. 5. Our results show that various species of diatoms as well as cyanobacteria can be of contrasting nutritional value for zooplankton because of their different content of the essential PUFAs. Diatoms, which are low in EPA, could not be considered as a valuable food, while some field populations of cyanobacteria might be valuable sources of essential ALA.     

SILICON UPTAKE BY ALGAE WITH NO KNOWN Si REQUIREMENT. I. TRUE CELLULAR UPTAKE AND pH-INDUCED PRECIPITATION BY PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) AND PLATYMONAS SP. (PRASINOPHYCEAE)1

Phaeodactylum tricornutum Bohlin, the one diatom known to lack a silicon requirement for growth, and the prasinophyte Platymonas sp. are two representatives of a taxonomically diverse group of planktonic algae that have been reported to take up Si without a demonstrable requirement for the element. For both species, removal of Si from solution during growth in batch culture has at least two components; true biological uptake throughout the growth of the culture, and spontaneous inorganic precipitation of a solid silicate phase–probably Mg₂Si₃O₈ (sepiolite)–under the elevated pH conditions that prevail late in batch growth. It is not clear to what extent previous observations of Si uptake by algae without siliceous frustules may be influenced by inorganic, non-cellular precipitation. The kinetics of true cellular uptake of Si are similar in Phaeodalylum and Platymonas, and different from those reported for the Si-requiring diatoms. Uptake follows hyperbolic saturation kinetics in both species, with half-saturation concentrations of 97.4 μM in Phaeodactylum and 80.9 μM in Platymonas, as compared to ca. 1–6 μM in diatoms that form siliceous frustules. Uptake by Phaeodactylum and Platymonas is not substrate-saturated until the dissolved Si concentration of the medium exceeds 200 μM. Concentrations this high do not occur in the surface layer of the ocean, and the kinetics suggest that both species deposit much less silica in nature than they can be induced to deposit in culture.     

Spatial and temporal variation in community composition and photosynthetic characteristics of phytoplankton in the upper Westerschelde estuary (Belgium,SW Netherlands)

Community composition, biomass and primary production of phytoplankton were studied in the east- ernmost section of the Westerschelde estuary in 1984. Photosynthetic characteristics were compared with distribution of some dominant phytoplankton species along a salinity gradient from 5 to 22 Spring phytoplankton, with Cyclotella meneghiniana (freshwater) and Skeletonema costatum (marine) as the dominant species grew faster than summer phytoplankton. In summer, biomass achieved its maximum, due to the riverine Scenedesmus species and the marine diatoms Thalassiosira levanderi and Ditylum brightwellii, as dominants. Growth conditions were more favourable to phytoplankton communities above 15%, than below this salinity. The data were compared with previous studies (1972) of species composition in the area.     

<Emphasis Type="Italic">Prorocentrum rivalis</Emphasis> sp. nov. (Dinophyceae) and its phylogenetic affinities inferred from analysis of a mixed morphological and LSU rRNA data set

A new freshwater epiphytic Prorocentrum species, Prorocentrum rivalis, from the temperate region of the Haute-Vienne, France, is described. This species is the third freshwater species identified among approximately 60 marine Prorocentrum species. This new species is described using scanning electron microscope and phylogenetic analyses by a polyphasic approach (LSU rRNA sequences combined with 9 morphological characters). The phylogenetic analysis attests that P. rivalis is close to other planktonic freshwater species and the freshwater Prorocentrum clade is evolutionarily derived from an epiphytic freshwater prorocentroid ancestor. The unique marine species in the freshwater clade results from an ecophysiological reversion. P. rivalis differs from other epiphytic taxa by its rarity, its temperate distribution and its ecophysiological needs. The phylogeny confirms also that all planktonic Prorocentrum species are evolutionarily derived from epiphytic/benthic ancestors.     

Microphytobenthic Primary Production and Sedimentary Carbohydrates Along Salinity Gradients in the Lagoons of Grado and Marano (Northern Adriatic Sea)

Primary production of the microphytobenthic community and carbohydrates concentrations were studied in the lagoonal system of Grado and Marano, located in the Northern Adriatic coast. Sediment samples were collected along a salinity gradient. Abundance and species composition of the microphytobenthic communities were analysed and the benthic microalgal biomass was estimated as Chlorophyll a (Chl a). Primary production of benthic diatoms was estimated using ¹⁴C-tracer. Extracellular carbohydrates were extracted from the sediment and separated in two operationally defined fractions (colloidal and EDTA-extractable). Salinity was higher in the Grado lagoon, where the benthic microalgal community was mainly composed of marine diatoms. In the Marano lagoon, which has a lower salinity, freshwater species were also found. In both lagoons, photosynthetic efficiency showed an inverse relationship with salinity and a direct relationship with the main biological variables. Photosynthetic activity was directly related to Chl a and abundance of benthic microalgae, suggesting that in the benthic system microalgal community is responsible for primary production. Overall, salinity was also influent on the microphytobenthic primary production, which was greater in the more saline Grado lagoon.     

ENVIRONMENTAL FACTORS INFLUENCING DIATOM CELL MOTILITY1

This article describes the effect of various environmental conditions on the speed of freshwater diatoms. The diatoms display a wide distribution of cell speeds, from 0 to > 20 μm·s^?l, as indicated by both the distribution of speeds within a cell population as well as the distribution of 1-s interval speeds of individual cells. Cell length has little or no effect on cell speed, as the speed of large postconjugal populations of Craticula and smaller preconjugal cell populations were not significantly different. The diatoms showed a broad pH tolerance, with Craticula spp. and Nitzschia spp. displaying active motility between pH 3 and 12 and pH 4 and 10, respectively, with velocity maxima for both species at approximately pH 7. In contrast to previous reports on marine diatoms, these freshwater diatoms do not require millimolar levels of external calcium for motility, as both Craticula spp. and Nitzschia spp. showed significant motility in distilled water (<0.5 μM calcium) for up to 5 h. Although addition of ≥500 μM of EGTA inhibited motility, this inhibition did not appear to be due to calcium chelation, as EGTA solutions preincubated with up to 20-fold excess calcium, magnesium, or both still inhibited motility with the same dose-dependent response as EGTA alone. Moreover, significant motility was restored by rinsing EGTA-treated cells in distilled water, Ca-free medium, or regular diatom medium. The calcium channel inhibitors lanthanum and ruthenium red also inhibited motility in a dose-dependent manner, suggesting that regulation of internal calcium stores may be important in motility. Craticula motility also declines rapidly in medium ≥50 mOsM while the isotonic concentration appears to be 100–120 mOsM, suggesting that movement may require the plasma membrane to be exerting a force ≥50–70 mOsM osmotic pressure (1–1.5 atm) against the cell wall.     

Life history and feeding habits of the marine nematode,Chromadora macrolaimoides steiner

Summary Chromadora macrolaimoides Steiner, a free-living nematode present in the aufwuchs assemblages of several marine macrophytes located in North Sea Harbor, Southampton, New York, was isolated from Enteromorpha intestinalis and established in laboratory culture, where its life history and feeding habits were studied. Under the experimental conditions (25 C and 26 S) the worm has an average generation time (22 days) and average life span (45 days) similar to other chromadorids which have been studied in the laboratory.Tracer-feeding experiment with ³²P-labelled bacteria, diatoms and chlorophytes indicate selectivity by the worm in both the ingestion and apparent digestion of potential food organisms, with the diatoms and chlorophytes being the preferred foods. Out of a total of 20 species of algae and 14 species of bacteria, two species of diatoms (Nitzschia acicularis and Cylindrotheca closterium) were found which are capable of sustaining indefinite growth. Bacteria-free culture has not been established, however, due to the extreme sensitivity of the worm to antibioties.A comparison of the feeding habits of C. macrolaimoides with Rhabditis marina, another marine nematode fed the same potential food organisms is made, and the influence of selective feeding on the spatial and temporal distribution of marine nematodes is discussed.This work was supported by National Science Foundation Grant GB-19245Contribution No. 15 from the Institute of Oceanography, City University of New York     

Comparing the low‐salinity tolerance of Ulva species distributed in different environments

The green macroalgal genus Ulva (Ulvales, Ulvophyceae, Chlorophyta) is distributed worldwide from marine to freshwater environments. Comparative analyses of hyposalinity tolerance among marine, brackish, and freshwater Ulva species were performed by fluorescein diacetate viability counts. The subtidal marine species Ulva sp., collected from a depth of 30 m, showed the poorest tolerance to low salinity. This species died in 5 practical salinity units (PSU) artificial seawater or freshwater within 1 day. Its closely related species U. linza L. (an intertidal species) and U. prolifera Müller (a brackish species) showed varying tolerances to low salinity. After 7 days of freshwater exposure, the viability of U. linza L. decreased to approximately 20%, while U. prolifera Müller showed nearly 100% viability. The freshwater species U. limnetica Ichihara et Shimada, not yet found in coastal areas, was highly viable in seawater.