Navicula Directa Research Articles

Effects of elevated pCO2 on the photosynthetic performance of the sea ice diatoms Navicula directa and Navicula glaciei

Effects of elevated pCO2 on the photosynthetic performance of the sea ice diatoms Navicula directa and Navicula glaciei

Postglacial palaeoenvironmental reconstruction of the Fury and Hecla Strait region (Nunavut) inferred from microfossils and geochemical proxies

Postglacial palaeoenvironmental reconstruction of the Fury and Hecla Strait region (Nunavut) inferred from microfossils and geochemical proxies

Changes in Sea-Ice Protist Diversity With Declining Sea Ice in the Arctic Ocean From the 1980s to 2010s

The large declines in Arctic sea-ice age and extent over the last decades could have altered the diversity of sea-ice associated unicellular eukaryotes (referred to as sea-ice protists). A time series from the Russian ice drift stations from the 1980s to the 2010s revealed changes in community composition and diversity of sea-ice protists from the central Arctic Ocean. However, these observations have been biased by varying levels of taxonomic resolution and sampling effort, both of which were higher in the early years at drift stations on multiyear sea ice (MYI) in the central Arctic Ocean. We here combine the Russian ice-drift station data with more recent data to (1) identify common sea-ice protists (in particular diatoms) in drifting sea ice of the central Arctic Ocean; (2) characterize the potential change in such communities over 35 years in terms of species number and/or community structure; and (3) relate those shifts to relevant environmental factors. In terms of relative abundance, pennate diatoms were the most abundant sea-ice protists across the Arctic, contributing 60% on average of counted cells. Two pennate colony-forming diatom species, Nitzschia frigida and Fragilariopsis cylindrus, dominated at all times, but solitary diatom species were also frequently encountered, e.g., Cylindrotheca closterium and Navicula directa. Multiyear ice contained 39% more diatom species than first-year ice (FYI) and showed a relatively even distribution along entire sea-ice cores. The decrease in MYI over the last decades explained the previously reported decreases in sea-ice protist diversity. Our results also indicate that up to 75% of diatom species are incorporated into FYI from the surrounding sea ice and the water column within a few months after the initial formation of the ice, while the remaining 25% are incorporated during ice drift. Thus, changing freeze-up scenarios, as currently witnessed in the Central Arctic, might result in long-term changes of the biodiversity of sea-ice protists in this region.

Removal of snow cover inhibits spring growth of Arctic ice algae through physiological and behavioral effects

The snow cover of Arctic sea ice has recently decreased, and climate models forecast that this will continue and even increase in future. We therefore tested the effect of snow cover on the optical properties of sea ice and the biomass, photobiology, and species composition of sea ice algae at Kangerlussuaq, West Greenland, during March 2011, using a snow-clearance experiment. Sea ice algae in areas cleared of snow was compared with control areas, using imaging variable fluorescence of photosystem II in intact, unthawed ice sections. The study coincided with the onset of spring growth of ice algae, mainly an increase in two pennate diatoms (Achnanthes taeniata and Navicula directa), as temperature increased and ice thickness and brine volume stabilized. The increase in biomass was accompanied by an increase in minimum variable fluorescence (F o) and the maximum quantum yield of PSII (F v /F m) and filling of brine channels with fluorescing cells. In contrast, in the minus snow area, PAR transmittance increased sixfold and there was an exponential decrease in chl-a and no increase in F o, and the area of fluorescing biomass declined to become undetectable. This study suggests that the onset of the spring bloom is predominantly due to temperature effects on brine channel volume, and that the algal decline after snow removal was primarily due to emigration rather than photodamage.

Field Emission Scanning Electron Microscopy (FESEM) characterisation of the porous silica nanoparticulate structure of marine diatoms

Diatoms are unicellular algae that synthesize cell wall with silica that has highly ornate features on the nano to microscale. The porous silica nanoparticulate structure of three marine centric and one pennate diatoms namely, Coscinodiscus concinnus, Coscinodiscus sp., Odontella mobiliensis and Navicula directa were investigated by Field Emission Scanning Electron Microscopy (FESEM). Important morphological features like porous pattern, topography, pore size and shape were studied. The external layer (cribellum) of C. concinnus was found to be consisting of a characteristic pentagonal array of pores which were star in shape and irregular in size, with a diameter of 224.7 nm and a pore-to-pore distance of 160.6 nm. The second diatom species investigated, Coscinodiscus sp. showed frustule with radially-oriented pattern of alternating grid-like arrangements of pores with honeycomb topography with pore diameter of 132.1 and distance between arrays were 61.01 nm. The O. mobiliensis images showed well organisation of holes (foramen) showed hexagonal organisation and all the pores are circular with same size and pores of 328.6 nm diameter with pore to pore distance was 252.8 nm. The girdle view of N. directa was about 5 μm in diameter with values showing striae are parallel in whole and porous were observed in N. directa in the range of 278.3 nm, the gaps between regularly arranged pores were 145.6 nm was clearly observed. The internal and external structures of all the diatom frustules were different in pore arrangements. The present study showed that high-resolution FESEM results revealed the silica nanostructure with nanoporous material exhibited interesting application in antireflection, drug delivery and heavy metal adsorbing studies, which should be investigated further research will be a subject of future proposals by a flat form of present investigation.

The effect of surface colour on the formation of marine micro and macrofouling communities

The effect of substratum colour on the formation of micro- and macro fouling communities was investigated. Acrylic tiles, painted either black or white were covered with transparent sheets in order to ensure similar surface properties. All substrata were exposed to biofouling at 1 m depth for 40 d in the Marina Bandar al Rowdha (Muscat, Sea of Oman). Studies were conducted in 2010 over a time course of 5, 10 and 20 d, and in 2012 samples were collected at 7, 14 and 21 d. The densities of bacteria on the black and white substrata were similar with the exception of day 10, when the black substrata had a higher abundance than white ones. Pyrosequencing via 454 of 16S rRNA genes of bacteria from white and black substrata revealed that Alphaproteobacteria and Firmicutes were the dominant groups. SIMPER analysis demonstrated that bacterial phylotypes (uncultured Gammaproteobacteria, Actibacter, Gaetbulicola, Thalassobius and Silicibacter) and the diatoms (Navicula directa, Navicula sp. and Nitzschia sp.) contributed to the dissimilarities between communities developed on white and black substrata. At day 20, the highest amount of chlorophyll a was recorded in biofilms developed on black substrata. SIMPER analysis showed that Folliculina sp., Ulva sp. and Balanus amphitrite were the major macro fouling species that contributed to the dissimilarities between the communities formed on white and black substrata. Higher densities of these species were observed on black tiles. The results emphasise the effect of substratum colour on the formation of micro and macro fouling communities; substratum colour should to be taken into account in future studies.

The influence of increased temperature and carbon dioxide levels on the benthic/sea ice diatom Navicula directa

Polar oceans are very susceptible to increased levels of atmospheric CO2 and may act as the world’s largest sink for anthropogenic CO2. Simultaneously, as atmospheric CO2 increases, sea surface temperature rises due to global warming. These two factors are important in regulating microalgal ecophysiology, and it has been suggested that future global changes may significantly alter phytoplankton species composition. This study aims to investigate potential consequences of global change in terms of increased temperature and CO2 enrichment on the benthic/sea ice diatom Navicula directa. In a laboratory experiment, the physiological response to elevated temperature and partial pressure of CO2 (pCO2) was investigated in terms of growth, photosynthetic activity and photosynthetic pigment composition. The experiment was performed under manipulated levels of pCO2 (380 and 960 ppm) and temperature (0.5 and 4.5°C) to simulate a change from present levels to predicted levels during a worst-case scenario by the year 2100. After 7 days of treatment, no synergetic effects between temperature and pCO2 were detected. However, elevated temperature promoted effective quantum yield of photosynthesis (∆F/ $$ F^\prime_{\rm m} $$ ) and increased growth rates by approximately 43%. Increased temperature also resulted in an altered pigment composition. In addition, enrichment of CO2 appeared to reduce specific growth rates of N. directa. Even though growth rates were only reduced by approximately 5%, we hereby report that increased pCO2 levels might also have potential negative effects on certain diatom strains.

Short-term variability of water quality and its implications on phytoplankton production in a tropical estuary (Cochin backwaters—India)

Changes in the phytoplankton biomass (chlorophyll a), production rate, and species composition were studied over two seasons using the time series measurements in the northern limb of the Cochin estuary in relation to the prevailing hydrological conditions. The present study showed the significant seasonal variation in water temperature (F=69.4, P<0.01), salinity (F=341.93, P<0.01), dissolved inorganic phosphorous (F=17.71, P<0.01), and silica (F=898.1, P<0.01) compared to nitrogen (F=1.646, P>0.05). The uneven input of ammonia (3.4-224.8 μM) from upstream (Periyar River) leads to the inconsistency in the N/P ratio (range 6.8-262). A distinct seasonality was observed in Si/N (F=382.9, P<0.01) and Si/P (F=290.3, P<0.01) ratios compared to the N/P ratio (F=1.646, P>0.05). The substantial increase in chlorophyll a (average, 34.8±10 mg m(-3)) and primary production (average, 1,304±694 mg C m(-3) day(-1)) indicated the mesotrophic condition of the study area during the premonsoon (PRM) and it was attributed to the large increase in the population of nanoplankton (size<20 μ) such as Skeletonema costatum, Thalassiosira subtilis, Nitzschia closterium, and Navicula directa. In contrast, during the post monsoon (PM), low chlorophyll a concentration (average, 9.3±9.2 mg m(-3)) and primary production (average, 124±219 mg C m(-3) day(-1)) showed heterotrophic condition. It can be stated that favorable environmental conditions (optimum nutrients and light intensity) prevailing during the PRM have enhanced the abundance of the nanoplankton community in the estuary, whereas during the PM, the light limitation due to high turbidity can reduce the nanoplankton growth and abundance, even though high nutrient level exists.

DEVELOPMENT OF IMMUNOASSAYS FOR THE IRON-REGULATED PROTEINS FERREDOXIN AND FLAVODOXIN IN POLAR MICROALGAE(1).

While the growth of Southern Ocean phytoplankton is often limited by iron availability, there are no comparable experiments on sea-ice algae. Here we assess the use of ferredoxin and flavodoxin to investigate the iron nutritional status of sea-ice algae and describe the development of a quantitative immunoassay for both proteins in marine diatoms. High-affinity monoclonal antibodies toward both proteins were produced from Cylindrotheca closterium (Ehrenb.) J. M. Lewin et Reimann, and these were used to develop Western blots. Western blots run on whole protein extracts detected both proteins with little cross-reactivity toward other proteins. The two proteins could be successfully quantitated when applied to gels at between 5 and 50 ng in a volume of 25 μL (0.2-2 μg · mL(-1) ). Flavodoxin and ferrodoxin expression was examined in the Antarctic diatoms Entomoneis kjellmannii (Cleve) Poulin et Cardinal, Navicula directa (W. Sm.) Ralfs, Fragilariopsis curta (Van Heurck) Hust., Pseudo-nitzschia sp., Porosira glacialis (Grunow) E. G. Jørg., Fragilariopsis cylindrus (Grunow) Willi Krieg., Fragilariopsis sublinearis (Van Heurck) Heiden et Kolbe, C. closterium, Nitzschia lecointei Van Heurck, and the dinoflagellate Polarella glacialis Montresor, Procaccini et Stoecker. Two Arctic isolates were also examined, Nitzschia frigida (Grunow) and Fragilariopsis oceanica (Cleve) Hasle. Significant heterogeneity of protein expression was observed despite all cultures being grown in iron-replete f/2 medium. Only one species, F. cylindrus, displayed the expected expression of ferredoxin only in iron-replete medium. Four were observed to produce both proteins under iron-replete conditions. Ferredoxin was not detected at all in F. curta and Pseudo-nitzschia sp., but distinct flavodoxin bands were observed in both of these organisms. All species examined were observed to express either flavodoxin or ferredoxin or both of the proteins as determined by Western immunoblotting.

Antiviral Sulfated Polysaccharide from Navicula directa, a Diatom Collected from Deep-Sea Water in Toyama Bay

A sulfated polysaccharide named naviculan was isolated from a diatom, Navicula directa (W. SMITH) RALFS, collected in deep sea water from Toyama Bay. The polysaccharide consisted of fucose, xylose, galactose, mannose, rhamnose and sulfate with an apparent molecular weight of 220000. It showed antiviral activities against herpes simplex viruses type 1 and 2, and influenza A virus with selectivity indices (CC50/IC50) of 270, 510 and 32, respectively. Naviculan also showed an inhibitory effect on cell-cell fusion between CD4-expressing and human immunodeficiency virus (HIV) gp160-expressing cells that was used as a model system of infection with HIV.

EFFECTS OF METAL AND PETROLEUM HYDROCARBON CONTAMINATION ON BENTHIC DIATOM COMMUNITIES NEAR CASEY STATION, ANTARCTICA: AN EXPERIMENTAL APPROACH1

The effects of metals and petroleum hydrocarbons on benthic marine diatom communities were assessed using a manipulative field experiment at Casey Station, Antarctica. Uncontaminated, metal contaminated, and petroleum hydrocarbon contaminated sediments were deployed for 11 weeks during the 1999 austral summer. The treatments were deployed at three different locations: Brown Bay, which has elevated levels of anthropogenic contaminants, and two uncontaminated reference locations, O'Brien Bay and Sparkes Bay, the latter of which has naturally occurring high concentrations of some heavy metals. At each location, significant differences between the composition of diatom communities recruiting to control and petroleum hydrocarbon contaminated treatments were observed. Navicula directa (Smith) Ralfs occurred at lower abundances in the petroleum hydrocarbon contaminated treatments than in the control treatments. In contrast, Navicula cancellata Donkin occurred at higher relative abundances in both contaminated treatments relative to the control treatment. Interactions between treatment and location were also observed for several species, including Navicula glaciei Van Heurck. Significant differences in the overall community composition of diatom communities between control and metal contaminated treatments and metal contaminated and petroleum hydrocarbon contaminated treatments were only observed within Brown Bay. The location of deployment also had a significant influence on the composition of diatom communities. Brown Bay had higher abundances of Achnanthes brevipes Agardh but lower abundances of Navicula aff. cincta (Ehrenberg) Van Heurck than either reference locations. This experiment demonstrated that benthic diatom communities are sensitive to sediment contamination and would be suitable for future monitoring work within this and other areas of Antarctica.

Sexual auxosporulation of the marine diatom Navicula directa var. directa

SUMMARY Sexual auxosporulation was observed in a mixed culture of two strains of Navicula directa var. directa. Two gametes did not re-arrange in their gametangium and each adhered to the inner surfaces of the gametangial theca. Each of the two gametes of one gametangium fused with a gamete of the other gametangium iso-gamously. As a result, two zygotes and hence two auxo-spores were produced per paired gametangia. As the gametangial thecae kept close to the gametes during fusion, the zygote became associated with two different thecae. The presence of type IB2a of Geitler's (1973) system was confirmed by the present observations.

Cambios en la composición y abundancia de la comunidad microalgal del Pacífico colombiano, en relación con el evento "El Niño" 97-98

The composition of the Colombian Pacific microalgal community was affected by "El Niño" 97 — 98, increasing numbers and populations species fronn the dinoflagellates group and his covered area. At same time, the diatoms group decreasing his populations and species numbers. In relation with news species, Prorocentrum mexicanum presence was reported. This specie arrived lo the study area by displacement of the California 's Current to the north coastal zone by the warm current's effect. Cha etoceros aequatorialis, Asteromphalus arachne, Navicula directa, Palmeria hardmaniana, Alexandrium tropicale, Cladopixis brachiolata, Polykrikos kofoidii and Gonyaulax jollifei are reported in first time.