Search

Southern Ocean phytoplankton form the base of the Antarctic food web, influencing higher trophic levels through biomass and community structure. We examined phytoplankton distribution and abundance in the Indian Sector of the Southern Ocean during austral summer as part a multidisciplinary ecosystem survey: Trends in Euphausiids off Mawson, Predators and Oceanography (TEMPO, 2021). Sampling covered six meridional transects from 55-80°E, and from 62°S or 63°S to the ice edge. To determine phytoplankton groups, CHEMTAX analysis was undertaken on pigments measured using HPLC. Diatoms were the dominant component of phytoplankton communities, explaining 56% of variation in chlorophyll a (Chl a), with haptophytes also being a major component. Prior to sampling the sea ice had retreated in a south-westerly direction, leading to shorter ice-free periods in the west (< 44 days, ≤65°E) compared to east (> 44 days, ≥70°E), inducing a strong seasonal effect. The east was nutrient limited, indicated by low-iron forms of haptophytes, and higher silicate:nitrate drawdown ratios (5.1 east vs 4.3 west), pheophytin a (phaeo) concentrations (30.0 vs 18.4 mg m-2) and phaeo:Chl a ratios (1.06 vs 0.53). Biological influences were evident at northern stations between 75-80°E, where krill "super-swarms" and feeding whales were observed. Here, diatoms were depleted from surface waters likely due to krill grazing, as indicated by high phaeo:Chl a ratios (> 0.75), and continued presence of haptophytes, associated with inefficient filtering or selective grazing by krill. Oceanographic influences included deeper mixed layers reducing diatom biomass, and a bloom to the north of the southern Antarctic Circumpolar Current Front in the western survey area thought to be sinking as waters flowed from west to east. Haptophytes were influenced by the Antarctic Slope Front with high-iron forms prevalent to the south only, showing limited iron transfer from coastal waters. Cryptophytes were associated with meltwater, and greens (chlorophytes + prasinophytes) were prevalent below the mixed layer. The interplay of seasonal, biological and oceanographic influences on phytoplankton populations during TEMPO had parallels with processes observed in the BROKE and BROKE-West voyages conducted 25 and 15 years earlier, respectively. Our research consolidates understanding of the krill ecosystem to ensure sustainable management in East Antarctic waters. [ABSTRACT FROM AUTHOR]

Many parasitic Apicomplexa, such as Plasmodium falciparum, contain an unpigmented chloroplast remnant termed the apicoplast, which is a target for malaria treatment. However, no close relative of apicomplexans with a [...]

Ozone depletion and climate change are causing the Southern Annular Mode (SAM) to become increasingly positive, driving stronger winds southward in the Southern Ocean (SO), with likely effects on phytoplankton habitat due to possible changes in ocean mixing, nutrient upwelling, and sea ice characteristics. This study examined the effect of the SAM and 12 other environmental variables on the abundance of siliceous and calcareous phytoplankton in the seasonal ice zone (SIZ) of the SO. A total of 52 surface-water samples were collected during repeat resupply voyages between Hobart, Australia, and Dumont d'Urville, Antarctica, centred around longitude 142 ∘ E, over 11 consecutive austral spring–summer seasons (2002–2012), and spanning 131 d in the spring–summer from 20 October to 28 February. A total of 22 taxa groups, comprised of individual species, groups of species, genera, or higher taxonomic groups, were analysed using CAP analysis (constrained analysis of principal coordinates), cluster analysis, and correlation. Overall, satellite-derived estimates of total chlorophyll and measured depletion of macronutrients both indicated a more positive SAM was associated with greater productivity in the SIZ. The greatest effect of the SAM on phytoplankton communities was the average value of the SAM across 57 d in the previous austral autumn centred around 11 March, which explained 13.3 % of the variance in community composition in the following spring–summer. This autumn SAM index was significantly correlated pair-wise (p<0.05) with the relative abundance of 12 of the 22 taxa groups resolved. A more positive SAM favoured increases in the relative abundance of large Chaetoceros spp. that predominated later in the spring–summer and reductions in small diatom taxa and siliceous and calcareous flagellates that predominated earlier in the spring–summer. Individual species belonging to the abundant Fragilariopsis genera responded differently to the SAM, indicating the importance of species-level observation in detecting SAM-induced changes in phytoplankton communities. The day through the spring–summer on which a sample was collected explained a significant and larger proportion (15.4 %) of the variance in the phytoplankton community composition than the SAM, yet this covariate was a proxy for such environmental factors as ice cover and sea surface temperature, factors that are regarded as drivers of the extreme seasonal variability in phytoplankton communities in Antarctic waters. The impacts of SAM on phytoplankton, which are the pasture of the SO and principal energy source for Antarctic life, would have ramifications for both carbon export and food availability for higher trophic levels in the SIZ of the SO. [ABSTRACT FROM AUTHOR]

Ozone depletion and climate change are causing the Southern Annular Mode (SAM) to become increasingly positive, driving stronger winds southward in the Southern Ocean (SO), with likely effects on phytoplankton habitat due to changes in ocean mixing, nutrient upwelling, and sea ice. This study examined the effect of the SAM and other environmental variables on the abundance of siliceous and calcareous phytoplankton in the seasonal ice zone (SIZ) of the SO. Samples were collected during repeat transects between Hobart, Australia, and Dumont d'Urville, Antarctica, centred around longitude 142° E, over 11 consecutive austral spring-summers (2002-2012). Twenty-two taxa, comprised of species, genera or higher taxonomic groups, were analysed using CAP analysis, cluster analysis and correlation. The SAM significantly affected phytoplankton community composition, with the greatest influence exerted by a SAM index averaged across 57 days centred on 11th March in the preceding autumn, explaining 13.3% of the variance of taxa composition during the following spring-summer, and showing correlation with the relative abundance of 12 of the 22 taxa resolved. The day through the spring-summer that a sample was collected exerted the greatest influence on phytoplankton community structure (15.4% of variance explained), reflecting the extreme seasonal variation in the physical environment in the SIZ that drives phytoplankton community succession. The response of different species of Fragilariopsis spp. and Chaetoceros spp. differed over the spring-summer and with the SAM, indicating the importance of species-level observation in detecting subtle changes in pelagic ecosystems. This study indicated that higher SAM favoured increases in the relative-abundance of large Chaetoceros spp. that predominated later in the spring-summer and reductions in small diatom taxa and siliceous and calcareous flagellates that predominated earlier in the spring-summer. Such changes in the taxonomic composition of phytoplankton, the pasture of the SO and principal energy source for Antarctic life, may alter both carbon sequestration and composition of higher tropic levels of the SIZ region of the SO. [ABSTRACT FROM AUTHOR]

Australian scientist Shirley Jeffrey was a pioneer in oceanographic research, identifying the thentheoretical chlorophyll c, and was a worldwide leader in the application of pigment methods in quantifying phytoplankton as the foundation of the oceanic food supply. Her research paved the way for the successful application of microalgae in aquaculture around the world. Jeffrey earned bachelor's and master's degrees at University of Sydney, majoring in microbiology and biochemistry, followed by a PhD from the King's College London Hospital Medical School. Returning to Sydney, she was hired by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to research chlorophyll c. Following this successful effort, she became a research fellow at the University of California, Berkeley from 1962 to 1964. She then became affiliated with the Scientific Committee on Oceanic Research. After a 1973 sabbatical at the Scripps Institution of Oceanography in San Diego, she returned to CSIRO, where she spent the rest of her career. [ABSTRACT FROM AUTHOR]

Strengths of numerical relationships between phytoplankton abundance estimates made by microscopy and CHEMTAX have often been tested using regression analysis. To specifically test agreement, where data points lie along a line of equality, the Bland and Altman technique is commonly used in the medical literature and applied here to phytoplankton analysis for the first time (simultaneously with regression). Our analyses are based on a sample set collected off Coffs Harbour (∼ 30°S), Eastern Australia. While comparing abundance estimates of different phytoplankton pigment-types derived from microscopy and CHEMTAX we specifically aim at: (1) determining the usefulness of the Bland and Altman technique in comparing phytoplankton abundance estimates made by both quantification techniques, and (2) identifying the lowest taxonomic level (i.e., interclass or intraclass level) at which phytoplankton abundance estimates agree. Our results suggest that Bland and Altman analysis is highly suited to compare phytoplankton abundance estimates made by microscopy and CHEMTAX. It delivered a quantifiable difference of chlorophyll a concentrations between abundance estimates, which may benefit the future calibration of phytoplankton quantification techniques. Both Bland and Altman and regression analyses were suited to resolve imbalances between phytoplankton abundance estimates made by microscopy and CHEMTAX. Best agreement was found within dinoflagellates (class-level), poor agreement within three diatom pigment-types (intraclass level). We attributed the poor agreement within diatom abundance estimates to classification errors of microscopically determined taxa into pigment-types. Intraspecific pigment composition seems more variable than generally assumed, calling for studies resolving this variation to further conform abundance estimates made by microscopy and CHEMTAX. [ABSTRACT FROM AUTHOR]

Surface ocean productivity mediates the transfer of carbon to the deep ocean and in the process regulates atmospheric CO2 levels. A common axiom in oceanography is that large phytoplankton contribute disproportionally to the transfer of carbon to the deep ocean because of their greater ability to escape grazing pressure, build biomass, and sink. In the present study, we assessed the relationship of net community production to phytoplankton assemblages and plankton size distribution in the Sub-Antarctic Zone and northern reaches of the Polar Frontal Zone in the Australian sector of the Southern Ocean. We reanalyzed and synthesized previously published estimates of O2/Ar net community oxygen production (NCP) and triple-O2 isotopes gross primary oxygen production (GPP) along with microscopic and pigment analyses of the microbial community. Overall, we found that the axiom that large phytoplankton drive carbon export was not supported in this region. Mixed-layer-depth-integrated NCP was correlated to particulate organic carbon (POC) concentration in the mixed layer. While lower NCP/GPP and NCP/POC values were generally associated with communities dominated by smaller plankton size (as would be expected), these communities did not preclude high values for both properties. Vigorous NCP in some regions occurred in the virtual absence of large phytoplankton (and specifically diatoms) and in communities dominated by nanoplankton and picoplankton. We also observed a positive correlation between NCP and the proportion of the phytoplankton community grazed by microheterotrophs, supporting the mediating role of grazers in carbon export. The novel combination of techniques allowed us to determine how NCP relates to upper ocean ecosystem characteristics and may lead to improved models of carbon export. [ABSTRACT FROM AUTHOR]

Climate-driven changes are expected to alter the hydrography of the Sub-Antarctic Zone (SAZ) and Polar Frontal Zone (PFZ) south of Australia, in which distinct regional environments are believed to be responsible for the differences in phytoplankton biomass in these regions. Here, we report how the dynamic influences of light, iron and temperature, which are responsible for the photophysiological differences between phytoplankton in the SAZ and PFZ, contribute to the biomass differences in these regions. High effective photochemical efficiency of photosystem II (/0.4), maximum photosynthesis rate (), light-saturation intensity (), maximum rate of photosynthetic electron transport (1/), and low photoprotective pigment concentrations observed in the SAZ correspond to high chlorophyll and iron concentrations. In contrast, phytoplankton in the PFZ exhibits low / ( 0.2) and high concentrations of photoprotective pigments under low light environment. Strong negative relationships between iron, temperature, and photoprotective pigments demonstrate that cells were producing more photoprotective pigments under low temperature and iron conditions, and are responsible for the low biomass and low productivity measured in the PFZ. As warming and enhanced iron input is expected in this region, this could probably increase phytoplankton photosynthesis in this region. However, complex interactions between the biogeochemical processes (e.g. stratification caused by warming could prevent mixing of nutrients), which control phytoplankton biomass and productivity, remain uncertain. [ABSTRACT FROM AUTHOR]

The widespread coccolithophorid Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler plays a pivotal role in the carbon pump and is known to exhibit significant morphological, genetic, and physiological diversity. In this study, we compared photosynthetic pigments and morphology of triplicate strains of Southern Ocean types A and B/C. The two morphotypes differed in width of coccolith distal shield elements (0.11-0.24 μm, type A; 0.06-0.12 μm, type B/C) and morphology of distal shield central area (grill of curved rods in type A; thin plain plate in type B/C) and showed differences in carotenoid composition. The mean 19′-hexanoyloxyfucoxanthin (Hex):chl a ratio in type B/C was >1, whereas the type A ratio was <1. The Hex:fucoxanthin (fuc) ratio for type B/C was 11 times greater than that for type A, and the proportion of fuc in type A was 6 times higher than that in type B/C. The fuc derivative 4-keto-19′-hexanoyloxyfucoxanthin (4-keto-hex) was present in type A but undetected in B/C. DNA sequencing of tufA distinguished morphotypes A, B/C (indistinguishable from B), and R, while little variation was observed within morphotypes. Thirty single nucleotide polymorphisms were identified in the 710 bp tufA sequence, of which 10 alleles were unique to B/C and B morphotypes, seven alleles were unique to type A, and six alleles were unique to type R. We propose that the morphologically, physiologically, and genetically distinct Southern Ocean type B/C sensu be classified as E. huxleyi var. aurorae var. nov. S. S. Cook et Hallegr. [ABSTRACT FROM AUTHOR]

All photosynthetic organisms endeavor to balance energy supply with demand. For sea-ice diatoms, as with all marine photoautotrophs, light is the most important factor for determining growth and carbon-fixation rates. Light varies from extremely low to often relatively high irradiances within the sea-ice environment, meaning that sea-ice algae require moderate physiological plasticity that is necessary for rapid light acclimation and photoprotection. This study investigated photoprotective mechanisms employed by bottom Antarctic sea-ice algae in response to relatively high irradiances to understand how they acclimate to the environmental conditions presented during early spring, as the light climate begins to intensify and snow and sea-ice thinning commences. The sea-ice microalgae displayed high photosynthetic plasticity to increased irradiance, with a rapid decline in photochemical efficiency that was completely reversible when placed under low light. Similarly, the photoprotective xanthophyll pigment diatoxanthin (Dt) was immediately activated but reversed during recovery under low light. The xanthophyll inhibitor dithiothreitol (DTT) and state transition inhibitor sodium fluoride (NaF) were used in under-ice in situ incubations and revealed that nonphotochemical quenching (NPQ) via xanthophyll-cycle activation was the preferred method for light acclimation and photoprotection by bottom sea-ice algae. This study showed that bottom sea-ice algae from the east Antarctic possess a high level of plasticity in their light-acclimation capabilities and identified the xanthophyll cycle as a critical mechanism in photoprotection and the preferred means by which sea-ice diatoms regulate energy flow to PSII. [ABSTRACT FROM AUTHOR]

The distribution of euphausiid larvae along the coast of Terre Ade'lie, Antarctica, was assessed using oblique tows of a double-framed bongo net at 38 stations during summer 2004. Larvae of Euphausia crystallorophias and Thysanoessa macrura were observed. For E. crystallorophias larvae, the calyptopis I stage was dominant along the coast, while the most commonly observed stage of T. macrura was the furcilia. The distribution of E. crystallorophias larvae were correlated with abiotic factors, including depth and sea surface salinity, whereas those of T. macrura larvae were correlated with biotic factors, especially chlorophyll a and nitrate. Developmental stages of both species increased in age from west to east in the survey area, with younger developmental stages (metanauplius and calyptopis I) in the western part of the region and older stages (calyptopis II and III and furcilia I to VI) in the eastern part near the Mertz Glacier Tongue (MGT). It is suggested that these patterns could be linked with the water circulation and wind: near the MGT gyres could concentrate all developmental stages of both species near the coast, while katabatic winds near Dumont d'Urville will promote larval advection seawards, with younger stages near the coast and older stages further offshore. [ABSTRACT FROM AUTHOR]

1. Microbial plankton dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) were investigated over an austral summer (December 2002 to January 2003). The aim was to characterise carbon cycling in an environmentally extreme lake. 2. The lake had an unusual temperature profile with peak temperatures of 1.3–1.9 °C between 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom (110 m) on occasions. The ice cover underwent marked thinning and melting during the study period. 3. Chlorophyll a concentrations were consistently low, usually below 1 μg L−1, with highest concentrations close to the lake bottom, where the photosynthetic elements showed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between 34.9 × 104 L−1 ± 33.5 (23rd December) and 130.9 × 104 L−1 ± 112.3 (4th December). Highest photosynthetic activity was usually recorded below 25 m. Rates of carbon fixation varied between 0.089 μg C L−1 h−1 ± 0.002 and 0.579 μg C L−1 h−1 ± 0.156. Primary production was limited by low temperature and orthophosphate availability. 4. Mean bacterial concentration throughout the water column ranged between 9.3 × 107 L−1 ± 1.2 (23rd December) and 14.0 × 107 L−1 ± 1.8 (28th January). Bacterial production was low, less than 10% of primary production and ranged between 2.1 ng C L−1 h−1 ± 0.8 and 12 ng C L−1 h−1 ± 0.9. Highest rates coincided with times of highest primary production. On occasion dissolved organic carbon (DOC) concentrations dropped to 20 μg L−1, probably below accurate limits of detection, suggesting that carbon substratum and phosphorus may have limited bacterial growth. 5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of 26.6 × 104 L−1 ± 14.2 (23rd December) to 133.8 × 104 L−1 ± 33.5 (14th December). They imposed a significant grazing impact on the bacterioplankton, removing in excess of 100% of bacterial production in December. 6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below 600 μg L−1. The ratio of DOC : POC ranged between 0.44 : 1 and 2.8 : 1 in the upper 40 m of the water column, and 1.8 : 1 and 3.7 : 1 in the lower waters. The microbial plankton contributed 1–29% of POC, thus detrital POC made up the largest fraction of the POC pool. 7. Beaver Lake is an extreme lacustrine ecosystem where heterotrophic processes occasionally appear to be carbon limited. Significant summer ice-melt, not seen in a previous opportunistic sampling, may be having an impact on the carbon cycle. [ABSTRACT FROM AUTHOR]

Polarella glacialis(Montresor et al.) was identified in Davis Station sea ice by morphological and DNA sequence comparison of cultures with those of the authentic strainP. glacialisCCMP 1383 isolated from McMurdo Sound. Cells and cysts of the Davis isolate (FL1B) were morphologically indistinguishable fromP. glacialis, and comparison of the large subunit rDNA of both cultures demonstrated only 0.2% sequence divergence over 1366 base pairs. The photosynthetic pigments ofP. glacialis(strains FL1B and CCMP 1383) were typical of dinoflagellates, with peridinin (contributing up to 31%) as the major accessory pigment. Extremely high levels of polyunsaturated fatty acids (PUFA, up to 76.3%) were characteristic ofP. glacialisisolate FL1B. The high PUFA concentration of this species is thought to be an adaptation to survive the cold temperatures of the upper fast ice. The sterol profile of FL1B was atypical of dinoflagellates, with 4-desmethylsterols (up to 79%) in greater abundance than 4α-methyl sterols (up to 24%). 27-Nor-24-methylcholest-5,22E-dien-3β-ol was identified as the principle sterol inP. glacialis, contributing up to 64% of the total sterol composition. [ABSTRACT FROM AUTHOR]

A new potentially ichthyotoxic dinoflagellate genus, Takayama de Salas, Bolch, Botes et Hallegraeff gen. nov., is described with two new species isolated from Tasmanian (Australia) and South African coastal waters: T. tasmanica de Salas, Bolch et Hallegraeff, sp. nov. and T. helix, de Salas, Bolch, Botes et Hallegraeff, sp. nov. The genus and two species are characterized by LM and EM of field samples and laboratory cultures as well as large subunit rDNA sequences and HPLC pigment analyses of several cultured strains. The new Takayama species have sigmoid apical grooves and contain fucoxanthin and its derivatives as the main accessory pigments. Takayama tasmanica is similar to the previously described species Gymnodinium pulchellum Larsen, Gyrodinium acrotrochum Larsen, and G. cladochroma Larsen in its external morphology but differs from these in having two ventral pores, a large horseshoe-shaped nucleus, and a central pyrenoid with radiating chloroplasts that pass through the nucleus. It contains gyroxanthin-diester and a gyroxanthin-like accessory pigment, both of which are missing in T. helix. Takayama helix has an apical groove that is nearly straight while still being clearly inflected. A ventral pore or slit is present. It has numerous peripheral, strap shaped, and spiraling chloroplasts with individual pyrenoids and a solid ellipsoidal nucleus. The genus Takayama has close affinities to the genera Karenia and Karlodinium. [ABSTRACT FROM AUTHOR]

An obituary for biology researcher Shirley Winifred Jeffrey is presented.

Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This article reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed., (© 2014 John Wiley & Sons Ltd.)