Marine Planktonic Diatom Research Articles

Isolation and characterisation of a single-stranded DNA virus infecting the marine planktonic diatom Chaetoceros tenuissimus

Isolation and characterisation of a single-stranded DNA virus infecting the marine planktonic diatom Chaetoceros tenuissimus

Marine planktonic microbes survived climatic instabilities in the past

In the geological past, changes in climate and tectonic activity are thought to have spurred the tempo of evolutionary change among major taxonomic groups of plants and animals. However, the extent to which these historical contingencies increased the risk of extinction of microbial plankton species remains largely unknown. Here, I analyse fossil records of marine planktonic diatoms and calcareous nannoplankton over the past 65 million years from the world oceans and show that the probability of species' extinction is not correlated with secular changes in climatic instability. Further supporting these results, analyses of genera survivorship curves based on fossil data concurred with the predictions of a birth-death model that simulates the extinction of genera through time assuming stochastically constant rates of speciation and extinction. However, my results also show that these marine microbes responded to exceptional climatic contingencies in a manner that appears to have promoted net diversification. These results highlight the ability of marine planktonic microbes to survive climatic instabilities in the geological past, and point to different mechanisms underlying the processes of speciation and extinction in these micro-organisms.

Proposal of identification criteria for resting spores of Chaetoceros species (Bacillariophyceae) from a temperate coastal sea

Ishii K.-I., Iwataki M., Matsuoka K. and Imai I. 2011. Proposal of identification criteria for resting spores of Chaetoceros species (Bacillariophyceae) from a temperate coastal sea. Phycologia 50: 351–362. DOI: 10.2216/10-36.1Chaetoceros is a large, ecologically important genus of marine planktonic diatoms. Many species of Chaetoceros form resting spores to survive environmental stress. Species identification based on morphological characteristics of resting spores is difficult. In the present study, we proposed a flow diagram for the identification of Chaetoceros species based on morphology. Resting spores of 18 Chaetoceros species were identified in water and sediment samples from southern Japan and the East China Sea based on morphological characteristics of resting spores and/or the vegetative cells containing them. A single ring of puncta was found to be the most important morphological feature of resting spores for species identification, by which the positions of primary and secondary valves were correctly determined. Other morphological characteristics such as features of the primary valve face, margins of the primary and secondary valve mantles, and secondary valve face are also useful for species identification. A combination of these morphological characteristics was used to construct a flow diagram for identification of the 18 Chaetoceros species found in our samples with light microscopy. This flow diagram is most applicable to Japanese waters, but the approach should be refined and improved to understand the biology and ecology of Chaetoceros species in any marine ecosystem.

Limits to gene flow in a cosmopolitan marine planktonic diatom

The role of geographic isolation in marine microbial speciation is hotly debated because of the high dispersal potential and large population sizes of planktonic microorganisms and the apparent lack of strong dispersal barriers in the open sea. Here, we show that gene flow between distant populations of the globally distributed, bloom-forming diatom species Pseudo-nitzschia pungens (clade I) is limited and follows a strong isolation by distance pattern. Furthermore, phylogenetic analysis implies that under appropriate geographic and environmental circumstances, like the pronounced climatic changes in the Pleistocene, population structuring may lead to speciation and hence may play an important role in diversification of marine planktonic microorganisms. A better understanding of the factors that control population structuring is thus essential to reveal the role of allopatric speciation in marine microorganisms.

Morphology and ecology of the bloom-forming diatom Chaetoceros contortus from Peter the Great Bay, Sea of Japan

The morphology of the marine planktonic diatom Chaetoceros contortus Schutt from the Sea of Japan is described using light and electron microscopy. Because of morphological similarity, C. contortus was previously synonymized with the close species C. compressus Lauder by Gran and Yendo [22]. Abundant development of C. contortus was observed in 1997 in Amursky Bay (Sea of Japan). This species reached a maximum density of up to 1.3 × 106 cells/liter near the water surface in mid May 1997 in the period of water-column stratification.

Odour compounds of the diatom Cocconeis scutellum: effects on benthic herbivores living on Posidonia oceanica

Polyunsaturated aldehydes released by marine planktonic diatoms upon wounding have been extensively studied since the discovery that they reduce the hatching success of copepods. Diatoms are also abundant in benthic marine ecosystems. For this reason we investigated the pres- ence and the possible ecological roles of Cocconeis scutellum parva, a diatom found tightly attached to the leaves of Posidonia oceanica. This diatom was previously demonstrated to play an important trophic role for the shrimp Hippolyte inermis, by influencing its sex reversal. In the present study, C. scutellum parva was isolated and cultivated and the volatile compounds released upon cell disin- tegration were identified by mass-spectrometric methods. We demonstrated the presence of unsatu- rated aldehydes with chain lengths from C5 to C10. Unexpectedly, we found C6 compounds repre- sented by 3(Z)-hexenal, 2(E)-hexenal, hexanal and hexanol-1 that resemble the typical bouquet observed in higher plants. Compounds not described before for diatoms were, among others, pen- tane-2,3-dione and octane-2,3-dione. Food choice experiments performed on 17 animal species asso- ciated with P. oceanica meadows indicated that these grazers recognise the presence of the odour compounds, exhibiting complex patterns of reactions according to their life strategies. The mosaic of results obtained at various concentrations, in different species, indicated that wound-activated info- chemicals generate a web of communication among diatoms and benthic invertebrates.

Can Pseudo-nitzschia blooms be modeled by coastal upwelling in Lisbon Bay?

Marine planktonic diatoms of the genus Pseudo-nitzschia Peragallo have been responsible for amnesic shellfish poisoning (ASP) events worldwide through the production of the neurotoxin domoic acid (DA). In order to better understand the dynamics of the toxic events of Pseudo-nitzschia there is the need to describe their seasonal and spatial patterns. The main goal of this work is to establish the relation between a physical variable easily measured like coastal upwelling and the presence of Pseudo-nitzschia blooms, in Lisbon Bay. Phytoplankton samples were collected once a week from June 2001 to May 2005 and daily upwelling index were calculated based on values of geostrophic winds. Data of sea surface temperature, upwelling index, and Pseudo-nitzschia concentrations were used to construct statistical models to evaluate the seasonal variation and the relation between all parameters. Due to the nature of the time series involved in the study, it was applied the Zero-Inflated Generalized Poisson Regression Model. An initial spectral analysis was applied to the upwelling data in order to accurately understand the characteristics of the coastal upwelling. The results obtained indicate a close relation between upwelling events and Pseudo-nitzschia blooms which occurred during spring and summer. The mathematical model that describes Pseudo-nitzschia blooms in Lisbon Bay shows a lag of 4–6 days between the upwelling events and the presence of Pseudo-nitzschia in the monitoring station.

The time for sex: A biennial life cycle in a marine planktonic diatom

Whereas it is accepted that the population dynamics of higher organisms is strongly grounded in life history processes, such as the time taken to mature and reproduce, regulation in the abundance of aquatic protists is generally attributed to proximate properties of the environment in which they grow. We used 10 yr of data from the Gulf of Naples to determine the life history of a planktonic diatom, Pseudo‐nitzschia multistriata, through the analysis of cell abundances and cell size patterns. Asexual and sexual phases recurred with remarkable regularity. Maximum abundance occurred annually, between the end of summer and the beginning of autumn, but cohorts of large cells, derived from sexual events, were found only every second year. We developed a model of population growth, based on parameters determined from laboratory cultures, with further tuning using information from natural populations. The model simulated the birth, maturation, and disappearance of age classes like those in natural populations, but only when we imposed seasonal variation in the rate of cell division and timed sexual reproduction during the stationary phase of a bloom. The model predicts that P. multistriata will become locally extinct if sexual reproduction does not occur within 4 yr. Our data and model show that coherent life cycle properties can emerge in natural populations of unicellular organisms, analogous to those in multicellular organisms, as a result of finely tuned regulation of cell division and sexual competence.

Chemical interactions in diatoms: role of polyunsaturated aldehydes and precursors

Chemicals produced by aquatic organisms, and especially micro-organisms, have received increasing attention in the last decade for their role in shaping interactions and communities. Several cases emphasize the fact that chemical signals or defence may modulate interspecific interactions. Notably, it has been shown that diatoms, unicellular algae and key primary producers in aquatic ecosystems produce a wide range of bioactive metabolites. Among these compounds, polyunsaturated short-chain aldehydes in vitro strongly impair the reproduction of various potential grazers. In the field, the relationship between aldehyde production and reproductive failure in copepods remains unclear. Recent studies have suggested that these putative defence compounds may also be involved in intercellular communication and in interactions with competitors. Potential effects of the aldehyde precursors on various organisms have also been described. This review presents an overview of various results obtained in the last decade that could help us to understand the role of polyunsaturated aldehydes and their precursors in the ecology of diatoms. It is focused on the dichotomy between freshwater and marine environments. Indeed, most of the results on anti-proliferative aldehydes concern marine planktonic diatoms, whereas they are also known to be produced by benthic and freshwater species.

Lack of population genetic structuring in the marine planktonic diatom Pseudo-nitzschia pungens (Bacillariophyceae) in a heterogeneous area in the Southern Bight of the North Sea

Several marine holoplanktonic organisms show a high degree of geographically structured diversity for which it often remains unclear to what extent this differentiation is due to the presence of cryptic taxa. For the genetically distinct diatom Pseudo-nitzschia pungens var. pungens, we used six microsatellite markers to investigate the spatial and temporal genetic composition in the heterogeneous Southern Bight of the North Sea. Although our sampling area (ca. 100 km) comprised water bodies with different environmental conditions (marine, estuary, saline lake) and different degrees of connectivity (from complete isolation to supposedly free exchange between environments), no evidence of genetic differentiation was found. Expanding our sampling area (ca. 650 km), suggested a homogenous population structure over even larger areas in the North Sea. Our results suggest that the population structure of this diatom is mainly shaped by strong homogenizing effects of gene flow preventing genetic drift, even in water bodies with limited connectivity.

Natural Hybrids in the Marine Diatom Pseudo-nitzschia pungens (Bacillariophyceae): Genetic and Morphological Evidence

Hybridization between genetically distinguishable taxa provides opportunities for investigating speciation. While hybridization is a common phenomenon in various macro-organisms, natural hybridization among micro-eukaryotes is barely studied. Here we used a nuclear and a chloroplast molecular marker and morphology to demonstrate the presence of natural hybrids between two genetically and morphologically distinct varieties of the marine planktonic diatom Pseudo-nitzschia pungens (vars. pungens and cingulata) in a contact zone in the northeast Pacific. Cloning and sequencing of the rDNA internal transcribed spacer region revealed strains containing ribotypes from both varieties, indicating hybridization. Both varieties were found to also have different chloroplast-encoded rbcL sequences. Hybrid strains were either hetero- or homoplastidial, as demonstrated by denaturing gradient gel electrophoresis, which is in accordance with expectations based on the mode of chloroplast inheritance in Pseudo-nitzschia. While most hybrids are probably first generation, there are also indications for further hybridization. Morphologically, the hybrids resembled var. pungens for most characters rather than having an intermediate morphology. Further research should focus on the hybridization frequency, by assessing the spatial and temporal extent of the contact zone, and hybrid fitness, to determine the amount of gene flow between the two varieties and its evolutionary consequences.

Diversity dynamics of marine planktonic diatoms across the Cenozoic

Diatoms are the dominant group of phytoplankton in the modern ocean. They account for approximately 40% of oceanic primary productivity and over 50% of organic carbon burial in marine sediments. Owing to their role as a biological carbon pump and effects on atmospheric CO(2) levels, there is great interest in elucidating factors that influenced the rapid rise in diatom diversity during the past 40 million years. Two biotic controls on diversification have been proposed to explain this diversity increase: (1) geochemical coupling between terrestrial grasslands and marine ecosystems through the global silicon cycle; and (2) competitive displacement of other phytoplankton lineages. However, these hypotheses have not been tested using sampling-standardized fossil data. Here we show that reconstructions of species diversity in marine phytoplankton reject these proposed controls and suggest a new pattern for oceanic diatom diversity across the Cenozoic. Peak species diversity in marine planktonic diatoms occurred at the Eocene-Oligocene boundary and was followed by a pronounced decline, from which diversity has not recovered. Although the roles of abiotic and biotic drivers of diversification remain unclear, major features of oceanic diatom evolution are decoupled from both grassland expansion and competition among phytoplankton groups.

A Structural Study of Cadmium Interaction with Aquatic Microorganisms

The molecular mechanisms of cadmium toxicity for aquatic phototrophic microorganisms, reversible adsorption on the surface, and cellular uptake during growth were investigated by combining batch macroscopic experiments with atomic-level in situ Cd K-edge X-ray absorption fine structure spectroscopy. The following species were examined: marine planktonic (Skeletonema costatum, Thalassiossira weissflogil) and freshwater periphytic (Navicula minima, Achnanthidium minutissum) diatoms, cyanobacteria (Gloeocapsa sp.), anoxygenic phototrophic bacteria (Rhodopseudomonas palustris), and freshwater diatom-dominated biofilms. Upon short-term adsorption at the freshwater diatoms and cyanobacteria cell surface from a NaNO3 or NaCl solution, Cd is octahedrally coordinated by oxygen at an average distance of 2.27 +/- 0.02 angstroms and is associated with carboxylate groups. The atomic environment of cadmium incorporated into freshwater diatoms during long-term growth (operationally defined as Cd nonextracted by EDTA) is similar to that of adsorbed metal in terms of Cd-O first-shell distances and coordination numbers. Contrasting speciation is found for Cd incorporated into marine diatoms and adsorbed onto phototrophic anoxygenic bacteria R. palustris, where Cd is coordinated with three to five oxygen/nitrogen atoms and one to three sulfur atoms in the first atomic shell, likely in the form of cysteine/hystidine complexes or Cd-thiolate clusters. The Cd association with sulfhydryl groups in marine planktonic diatoms and anoxygenic bacteria is an important feature of Cd binding which can be useful for assessing the bioavailability of this metal.

Ecological functions of volatile organic compounds in aquatic systems

In terrestrial ecosystems, volatile organic compounds (VOCs) are widely acknowledged as an important group of infochemicals. They play a major role in pollinator attraction by terrestrial plants and as insect pheromones. Furthermore, they are the mediating agent of so-called ‘tritrophic interactions’. When plants are attacked by herbivorous insects, volatile signal substances are emitted, which act as attractants for parasitoids that kill the herbivores, thereby protecting the plant from herbivory. Despite the generally acknowledged importance of VOCs in terrestrial chemical ecology, their functions in aquatic food webs are largely unknown. VOCs produced by algae and cyanobacteria are a major concern in water processing, since aquatic primary producers are the reason for regularly encountered taste and odour problems in drinking water. Only very recently, research in aquatic chemical ecology has started to investigate possible ecological functions for the production of VOCs by algae and cyanobacteria. Volatile aldehydes released by wounded cells of marine planktonic diatoms seem to act as defensive compounds against herbivorous copepods on the population level. Just recently, it was found that VOCs released from benthic algae and cyanobacteria can be utilised as food and/or habitat finding cues by aquatic invertebrates such as freshwater gastropods and nematodes. Here, I review concepts and recent experimental studies on the ecological functions of such VOCs in aquatic ecosystems. Understanding the factors that lead to the liberation of volatile compounds is an essential prerequisite to properly assessing their ecological functions. It appears that (similar to terrestrial plant–herbivore interactions) VOCs can also play a steering role for both attraction and defence in aquatic ecosystems.

Seasonal variation in skeletal silicification of Neodenticula seminae, a marine planktonic diatom: Sediment trap experiments in the NW Pacific Ocean (1997–2001)

Neodenticula seminae is an important component of pelagic diatom floras in the subarctic North Pacific and its adjacent seas. We conducted an SEM image analysis of four series of samples collected by sediment traps in the NW Pacific, in order to investigate the relations between its morphology, evolution, and environment. Seasonal variation in the skeletal morphology was common: lightly silicified morphs were dominant during spring blooms and in the summer (under oligotrophic conditions owing to surface water stratification and progressive nutrient limitation), whereas heavily silicified morphs became abundant in the fall and winter, subsequent to the onset of intensive vertical mixing. These observations suggest that the morphology of N. seminae is influenced by environmental factors including the nutrient availability as well as by its reproductive strategy.

Climatically driven macroevolutionary patterns in the size of marine diatoms over the Cenozoic.

Numerous taxonomic groups exhibit an evolutionary trajectory in cell or body size. The size structure of marine phytoplankton communities strongly affects food web structure and organic carbon export into the ocean interior, yet macroevolutionary patterns in the size structure of phytoplankton communities have not been previously investigated. We constructed a database of the size of the silica frustule of the dominant fossilized marine planktonic diatom species over the Cenozoic. We found that the minimum and maximum sizes of the diatom frustule have expanded in concert with increasing species diversity. In contrast, the mean area of the diatom frustule is highly correlated with oceanic temperature gradients inferred from the delta18O of foraminiferal calcite, consistent with the hypothesis that climatically induced changes in oceanic mixing have altered nutrient availability in the euphotic zone and driven macroevolutionary shifts in the size of marine pelagic diatoms through the Cenozoic.

Growth dynamics of non-toxic Pseudo-nitzschia delicatissima and toxic P. seriata (Bacillariophyceae) under simulated spring and summer photoperiods

Marine planktonic diatoms of the genus Pseudo-nitzschia Peragallo have been responsible for amnesic shellfish poisoning (ASP) events worldwide through the production of the neurotoxin domoic acid (DA). The appearance and toxicity of Pseudo-nitzschia species is variable throughout the year and potentially linked to changes in environmental parameters; many ASP events occur in relatively high latitudes where day length is particularly variable with season. In UK waters, shellfish monitoring has prevented any impact on human health but has led to long-term closures of fisheries, with severe economic consequences. Laboratory experiments on two Pseudo-nitzschia species typically found in Scottish West Coast waters during spring (short photoperiod (SP)) and summer (long photoperiod (LP)) conditions were conducted to determine the influence of photoperiod on their growth and toxicity. Results indicated that non-toxic P. delicatissima (Cleve) Heiden achieved a greater cell density under SP (9-h light:15-h dark (L:D) cycle). For toxin-producing P. seriata (Cleve) H. Peragallo, a LP (18-h L:6-h D cycle) resulted in an enhanced growth rate, cell yield and total toxin production, but it decreased the toxin production per cell. A better understanding of the response of Pseudo-nitzschia species to photoperiod and other foreseeable environmental variables may help predict the appearance of toxic strains.

Pacific dulse (Palmaria mollis) as a food and biofilter in recirculated, land-based abalone culture systems

Palmaria mollis (Pacific dulse) is increasingly being used as an in situ biofilter and feed in land-based abalone culture. This work reviews physical and nutrient requirements for P. mollis culture and its nutritional value for three abalone species, the Japanese abalone Haliotis discus hannai, the red abalone Haliotis rufescens, and the U.S. Federally endangered white abalone Haliotis sorenseni.P. mollis growth was positively correlated with light over specific light densities (SLD) ranging from 0.0048 to 0.036molphotonsg−1fresh weightd−1, under tumble culture conditions. Under low light conditions, growth was greatest at a temperature of 12°C (SGR=8.69±0.29%d−1), while under high light conditions growth was greatest at a temperature of 14–18°C (SGR=10.5±0.12%d−1). Addition of Guillard's f nutrient medium [Guillard, R.R.L., Ryther, J.H., 1962. Studies on marine plankton diatoms. I. Cyclothella nana Huntedt and Detonula confercacae (Cleve). Gran. Can. J. Microbiol. 8, 229–239] significantly increased Pacific dulse growth in cultures receiving one seawater exchange per day; furthermore, growth was significantly improved by addition of trace metals. The use of NaNO3 as an N source in the f medium resulted in better growth compared with NH4NO3. The use of phosphorus additions above 83.3μMPd−1 depressed P. mollis growth rates. P. mollis growth was positively correlated with concentrations of dissolved inorganic carbon, including HCO3−. Growth rates were not significantly different over a pH range of 8.3–8.9.There were no significant toxic effects on Japanese abalone, H. discus hannai cultured in seawater supplemented with (0.75f+1.37μM Zn) trace metals d−1. H. discus hannai showed the highest growth rates when fed on P. mollis fertilized with f medium and nitrate (NO3−-N) loads ranging from 1176 to 2353μMd−1 while red abalone, H. rufescens, grew best when fed on P. mollis fertilized with f medium and nitrate loads of 2353–2942μMd−1. Both abalone species grew better on P. mollis fertilized with (0.75f+1.37μM Zn) d−1 trace metal solution compared with P. mollis without trace metal additions. H. sorenseni, grew well when fed on P. mollis, showing higher linear shell growth rates and higher survival rates compared with those of abalone fed on commercially harvested and abundant giant kelp, Macrocystis pyrifera.

Morphological study of the marine planktonic diatom Chaetoceros castracanei Karsten (Bacillariophyceae) from Antarctic waters, with a discussion on its possible taxonomic relationships

Phytoplankton samples were collected along the north coast of the Antarctic peninsula, the Weddell Sea and the Gerlache Strait, in different seasons in 1985, 1986, 1999, and 2000–2002. Chaetoceros castracanei Karsten, a fairly rare species was present in the samples; its morphology, taxonomy and distribution have not been recently investigated. This species occurred mainly from January to April, and was recorded with relatively high abundances in the Weddell Sea (up to 9.5=104 cells l-1). C. castracanei forms straight or slightly curved, short to long chains, with the terminal and intercalary setae pointing in the same direction. The apertures are very reduced, centrally constricted, and there are numerous chloroplasts in the cells including the setae. Electron microscopy studies showed that valves are randomly perforated by round poroids, costae on the valve are absent, and an excentric rimoportula is present in every valve of the chain; the setae are circular in cross section at the base, but become four-sided distally. Setae have perpendicular rows of elongate poroids, spines are arranged in spirals along the setae and the tips are very pointed. The intercalary setae are fused together in sibling valves. Chaetoceros impressus Jensen et Moestrup, recently described from Danish waters, appears to be conspecific with C. castracanei, and consequently we propose it as a synonym of the latter. The known distribution of Chaetoceros castracanei may be broadened to include Antarctic, subantarctic and Danish waters, and also possibly more temperate regions.

Effect of pH on growth and domoic acid production by potentially toxic diatoms of the genera Pseudo-nitzschia and Nitzschia

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 273:1-15 (2004) - doi:10.3354/meps273001 Effect of pH on growth and domoic acid production by potentially toxic diatoms of the genera Pseudo-nitzschia and Nitzschia Nina Lundholm1,*, Per Juel Hansen1, Yuichi Kotaki2 1Marine Biological Laboratory, Strandpromenaden 5, 3000 Helsingør, Denmark 2School of Fisheries Sciences, Kitasato University, Sanriku, Ofunato 022-0101, Japan *Email: nlundholm@bi.ku.dk ABSTRACT: The effect of elevated pH on growth and on production of the neurotoxin domoic acid was studied in selected diatoms belonging to the genera Pseudo-nitzschia and Nitzschia. Growth of most of the 11 species studied stopped at pH values of 8.7 to 9.1. However, for P. delicatissima and N. navis-varingica the pH limit for growth was higher, 9.3 and 9.7 to 9.8, respectively. A compilation of all available data on the pH limits for growth of marine planktonic diatoms suggests that species from ponds and rock pools all have higher limits than coastal and oceanic species. Taking only coastal and oceanic species into account, the data suggest that smaller species have a higher upper pH limit for growth than larger species. Elevated pH induced production of domoic acid in P. multiseries in amounts comparable to those detected previously under silicate and phosphate limitation. As Pseudo-nitzschia species are found in high concentrations in nutrient-enriched areas, high pH and hence induction of the production of domoic acid would be expected during blooms. These results may help to understand when and why Pseudo-nitzschia species produce domoic acid in the field. KEY WORDS: Cell volume · Diatom · Domoic acid · Growth rate · pH · Phytoplankton · Pseudo-nitzschia · Toxin production Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 273. Online publication date: June 08, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.