Microalgal Community Composition Research Articles

Spatio-temporal dynamics in microalgal communities in Arctic land-fast sea ice

Sea ice microalgae are an important source of energy for the polar marine food web, representing the primary carbon source prior to pelagic phytoplankton blooms. Here we investigate community dynamics of sea ice microalgal communities in land-fast sea ice across six different fjords in high-Arctic Svalbard, Norway, during Spring (April – May). We found that light (0.1 – 23% incoming PAR / 0.1 – 193 μmol photons m-2s-1) played a central role in determining community composition, with more diverse assemblages observed in sites with more light transmitted to the bottom ice community. In April, microalgal assemblages were similar when under-ice light transmittance was similar, independent of geographical location, however this light-derived separation of community structure was not evident in May. At all sites, assemblages were dominated by pennate diatoms, with the most abundant taxon being Nitzschia frigida. However, with increasing under-ice light transmittance, we saw an increase in the relative abundance of Dinophyceae, Navicula spp. and Thalassiosira spp.. A positive relationship between light and δ13C enrichment and C:N ratios in the ice algal biomass demonstrated the effect of light on the biochemical composition of ice algae. Light did not correlate with cell abundance or chlorophyll a concentration. With anticipated changes to Arctic sea ice extent and snow cover as a result of climate change, we will see shifts in the light transmitted to the bottom ice community. These shifts, whether caused by reduced light transmittance from increased snow cover or increased light transmittance from thinning ice, snow depth or increased rainfall, will likely alter sea ice microalgal community composition, which in turn, may influence the success of secondary production and biogeochemical cycling in polar waters.

Electro-flocculation of aquaculture wastewater microalgal communities reduces nutrient loading

Land-based aquaculture provides dietary protein to the world’s population in a sustainable way, but issues related to release of nitrogen rich wastewater limits its expansion. Sedimentation of naturally occurring microalgae that assimilate excess nitrogen, is slow and land intensive. Electro-flocculation, used in wastewater treatment processes, is a potential alternative for aquaculture. Trials of different electro-flocculation configurations applied to three prawn farm pondwater samples containing varying microalgal assemblages are reported. In 64 % of trials, electro-flocculation reduced total nitrogen (TN) and dissolved inorganic nitrogen (DIN) loads within regulatory limits.TN was reduced up to 83.2 % (10.93 to 1.83 mg.L−1) within 20 mins in stationary water, and DIN to 90.6 % (3.19 to 0.30 mg.L−1) in 102 mins trials in flowing water. Bellerochea andGloeocapsa spp. were dominant in wastewater. The role of microalgal community composition on flocculation is discussed, including evidence Bellerocheapromotes flocculation. This study confirmed electro-flocculation quickly reduces TN and DIN.

Influence of heavy metals on the occurrence of Antarctic soil microalgae

AbstractHuman- and animal-impacted sites in Antarctica can be contaminated with heavy metals, as well as areas influenced by underlying geology and naturally occurring minerals. The present study examined the relationship between heavy metal presence and soil microalgal occurrence across a range of human-impacted and undisturbed locations on Signy Island. Microalgae were identified based on cultures that developed after inoculation into an enriched medium. Twenty-nine microalgae representing Cyanobacteria, Bacillariophyta, Chlorophyta and Tribophyta were identified. High levels of As, Ca, Cd, Cu and Zn were detected in Gourlay Peninsula and North Point, both locations hosting dense penguin rookeries. Samples from Berntsen Point, the location of most intense human activity both today and historically, contained high levels of Pb. The contamination factor and pollution load index confirmed that the former locations were polluted by Cd, Cu and Zn, with these being of marine biogenic origin. Variation in the microalgal community was significantly correlated with concentrations of Mn, Ca, Mg, Fe, Zn, Cd, Co, Cr and Cu. However, the overall proportion of the total variation contributed by all metals was low (16.11%). Other factors not measured in this study are likely to underlie the majority of the observed variation in microalgal community composition between sampling locations.

Distribution and diversity of eukaryotic microalgae in Kuwait waters assessed using 18S rRNA gene sequencing.

The microbial communities play a crucial role in ecosystem functioning through interactions among individuals and taxonomic groups in a highly dynamic marine ecosystem. The structure and functioning of the microbial communities are often influenced by the changes in the surrounding environment. Monitoring the microbial diversity of the marine ecosystem helps to understand spatial patterns of microbial community and changes due to season, climate, and various drivers of biological diversity. Kuwait is characterized by an arid environment with a high degree of temperature variation during summer and winter. Our understanding of spatial distribution patterns of microbial communities, their diversity, and the influence of human activities on the degree of changes in the diversity of the microbial community in Kuwait territorial waters remain unclear. In this study, we employed 18S rRNA sequencing to explore marine microalgal community composition and dynamics in seawater samples collected from Kuwait waters over two seasonal cycles across six locations. A total of 448,184 sequences across 36 replicates corresponding to 12 samples from six stations were obtained. The quality-filtered sequences were clustered into 1,293 representative sequences, which were then classified into different eukaryotic taxa. This study reveals that the phytoplankton community in Kuwait waters is diverse and shows significant variations among different taxa during summer and winter. Dinoflagellates and diatoms were the most abundant season-dependent microalgae taxa in Kuwait waters. Alexandrium and Pyrophacus were abundant in summer, whereas Gonyaulax was abundant during the winter. The abundance of Coscinodiscus and Navicula, of the diatom genera, were also dependent upon both seasonal and possible anthropogenic factors. Our results demonstrate the effectiveness of a sequencing-based approach, which could be used to improve the accuracy of quantitative eukaryotic microbial community profiles.

Contribution of microalgae to carbon sequestration in a natural karst wetland aquatic ecosystem: An in-situ mesocosm study

Carbonate rock weathering coupled with aquatic photosynthesis in karst areas is an important part in the formation of terrestrial carbon sinks. The capacity of photosynthetic carbon sequestration by aquatic microalgae and carbonic anhydrase (CA) is integral in the estimation of carbon sink potential of karst aquatic ecosystems. To date, carbon sequestration by aquatic microalgae in karst areas has been investigated in laboratory experiments. In the present work, the capacity of carbon sequestration by microalgae and CA under natural karst aquatic conditions and the main environmental factors were investigated in field in-situ mesocosms. The Sizhitan Pond of the Huixian karst wetland in Guilin City, Guangxi Province, China, was selected as a typical karst natural water body for this study. The capacity of photosynthetic carbon sequestration varied with microalgal community composition. The microalgal communities with active extracellular CA showed high capacity of carbon sequestration. The average conversion of inorganic carbon to relatively stable organic carbon by microalgae in the Huixian karst wetland aquatic ecosystem was estimated as 4207.5 t C/a. Approximately 28.7% of the bicarbonate fed by the karst underground river was fixed into organic carbon by microalgal photosynthesis. The major environmental factors affecting the capacity of carbon sequestration by microalgae in the karst wetland aquatic ecosystem were the water CA activity, illumination, temperature, total phosphorus and total nitrogen. This study is the first to address the contribution of aquatic microalgae and CA to carbon sequestration under natural karst aquatic conditions. The findings contribute to establishing groundwork for substantiating the carbon sink potential in global karst ecosystems.

Environmental factors controlling algal species succession in High Rate Algal Pond

In the last decade, studies have focused on identifying microalgal species responsible for wastewater treatment in high rate algal pond (HRAP). In this study, investigation of the microalgal community composition in Pilot-scale Race way-type high rate algal pond through study period of 24 months, chlorophyll “a” content was estimated, Physico-chemical parameters were analyzed, light intensity and temperature also measured, and the biomass productivity was calculated. It was found from the recorded results that, more than 19 genera of phytoplankton belonging to 4 divisions were identified with dominance variation throughout the study period. The presence of the species inside the pond is dependent on seasonal variation. Chemical analysis data exhibit a significant increase of COD, BOD, and TSS concentration with the temperature increase. There is an obvious impact of light intensity and temperature on the growth rate, where the highest growth response of 3.5 mg/l Chl. (a) was achieved at the highest light intensity of 1900 lux with a temperature degree of 39 °C. The average algal biomass produced from HRAP 0.99 kg algae/m3/d. This study demonstrates that the predominance of algal community structure affected by seasonal variations, and there are clear light intensity and temperature impact on the growth rate, as well as there was a promising production of algal biomass can be used in different aspects.

Biomarker evidence of algal-microbial community changes linked to redox and salinity variation, Upper Devonian Chattanooga Shale (Tennessee, USA)

Abstract Late Devonian marine systems were characterized by major environmental perturbations and associated biotic community changes linked to climate change and widespread oceanic anoxia. Here, we provide high-resolution lipid biomarker chemostratigraphic records from the Upper Devonian Chattanooga Shale (Tennessee, USA) to investigate algal-microbial community changes in the southern Illinois Basin that were related to contemporaneous shifts in marine redox (as proxied by trace metals, Fe-species, and Corg/P) and salinity conditions (as proxied by B/Ga, Sr/Ba, and S/total organic carbon). The Frasnian was characterized by dominantly bacterial lipids (high hopane/sterane), near-marine salinity, and a shift from oxic to increasingly reducing conditions in response to increasing organic carbon sinking fluxes. Aryl isoprenoids and aryl isoprenoid ratios reveal that the O2-H2S chemocline was unstable and intermittently shallow (i.e., within the photic zone). The Frasnian-Famennian boundary was marked by a shift in microalgal community composition toward green algal (e.g., prasinophyte) dominance (lower C27 and higher C28 and C29 steranes), a sharp reduction in watermass salinity, and a stable O2-H2S chemocline below the photic zone, conditions that persisted until nearly the end of the Famennian. We infer that changing watermass conditions, especially a sharp reduction in salinity to possibly low-brackish conditions (<10 psu), were the primary cause of concurrent changes in the microalgal community, reflecting tolerance of low-salinity conditions by green algae. Transient spikes in moretane/hopane (M/H) ratios may record enhanced terrestrial weathering at the Frasnian-Famennian and Devonian–Carboniferous boundaries, triggered by coeval glacio-eustatic falls and increased inputs of soil organic matter. High M/H and pristane/phytane, in combination with low chemical index of alteration and K/Al, record a decrease in chemical weathering intensity during the Famennian that may have been due to contemporaneous climatic cooling, and a concurrent reduction in silt content may reflect stabilization of land surfaces by vascular plants and resulting reduced sediment yields. This study demonstrates the effectiveness of combining organic and inorganic geochemical proxies (including novel paleosalinity indices) for determination of environmental controls on the composition and productivity of plankton communities in paleomarine systems.

Environmental drivers that influence microalgal species in fullscale wastewater treatment high rate algal ponds

In the last decade, studies have focused on identifying the most suitable microalgal species for coupled high rate algal pond (HRAP) wastewater treatment and resource recovery. However, one of the challenges facing outdoor HRAP systems is maintaining microalgal species dominance. By increasing our understanding of the environmental drivers of microalgal community composition within the HRAP environment, it may be possible to manipulate the system in such a way to favour the growth of desirable species. In this paper, we investigate the microalgal community composition in two full-scale HRAPs over a 23-month period. We compare wastewater treatment performance between dominant species and identify the environmental drivers that trigger change in community composition. A total of 33 microalgal species were identified over the 23-month period but species richness (the number of species present at any given time) was low and was not related to either productivity or nutrient removal efficiency. Species turnover of the dominant microalgae happened rapidly, typically <1 week. Changes in the influent NH4-N concentration and zooplankton grazer numbers were significantly associated with species turnover, accounting for 80% of the changes in dominant species throughout the 23-month study period. Both nutrient removal and biomass production did not differ between the two HRAPs when the dominant species was the same or differed in the two ponds. These results suggest that microalgal functional groups are more important than individual species for full-scale HRAP performance. This study has increased our understanding of some of the environmental drivers of the microalgae within the HRAP environment, which may assist with improving wastewater treatment and resource recovery.

A review of microalgae as indicators in South African estuaries

Microalgae are one of the most important components of estuarine ecosystems, providing the fuel required to sustain higher trophic levels. Being at the base of aquatic food webs, these communities are generally the first to respond to anthropogenic disturbances – particularly opportunistic species – and can often be used effectively as indicators of ecosystem health. The purpose of this review is to assess the status of estuarine microalgal research in South Africa and to highlight the shortcomings of past research and identify priorities for future research. What became apparent during a synthesis of South African literature on the topic, was that the broad ecology of microalgae – both phytoplankton and microphytobenthos – has been well addressed. Generally speaking, the interaction between freshwater inflow and microalgal communities has formed the basis for the majority of this research. This trend was logical due to South Africa being a relatively arid country, where demand for freshwater often exceeds supply. In terms of microalgal studies however, numerous shortcomings can be identified, including the lack of: (1) thorough assessments of microalgal community composition; (2) conclusive demonstration of the role of suggested indicator species; (3) adequate sampling periods and/or intensity; and (4) fine-scale experimental research – both in situ and laboratory. A concern on a broader scale, and in stark contrast to Europe and the United States, is the lack of explicit assessment of what comprises eutrophication in South African estuaries. Finally, and perhaps the most pertinent theme identified in this review is the necessity for adopting ‘hypothesis-driven research’.

Microalgal species variation at different successional stages in biological soil crusts of the Gurbantunggut Desert, Northwestern China

Biological soil crusts (BSC), most notably lichen crusts, develop and diversify in the Gurbantunggut Desert, the largest fixed and semi-fixed desert in China. Four different successional stages of BSC, including bare sand, microalgal crusts, lichen crusts, and moss crusts, were selected to determine successional changes in microalgal species composition and biomass and formation of BSC. A 10 × 10-m observation plot was established in an interdune region of the Gurbantunggut Desert and data were collected over an 8-year study period. The main results were: (1) different successional stages of BSC significantly affected the content of soil organic C and total and available N but not the total and available P and K content of soil; (2) composition of microalgal communities differed among the four successional stages; (3) significant differences in microalgal biomass were observed among the four successional stages; (4) bare sand was mainly uncompacted sand gains; (5) filamentous cyanobacteria, particularly Microcoleus vaginatus, were the dominant species in the early phase of crust succession. The presence of fungal mycelium and moss rhizoids prevented water and wind erosion.

Planktonic and benthic microalgal community composition as indicators of terrestrial influence on a fringing reef in Ishigaki Island, Southwest Japan

Microalgal-based indicators were used to assess terrestrial influence on Shiraho coral reef of Ishigaki Island (Okinawa, Japan). A typhoon occurred on 4–5 August 2005 and sampling were made on three occasions thereafter (6, 8, and 11 August). Pre-typhoon sampling was conducted on 26 July. The typhoon-enhanced terrestrial discharges increased reef nutrient levels (e.g. average NO 3 - -N: 0.088 mg/L pre-typhoon to 0.817 mg/L post-typhoon). This elevated chlorophyll- a concentrations by four times and shifted phytoplankton composition (spectral class-based) from an initial dominance of diatoms and green microalgae to the dominance of bluegreen microalgae (cyanobacteria) and cryptophytes. Cyanobacteria later increased by more than 200% and accounted for as much as 80% of total chl- a (∼0.29 μg/L), possibly assisted by favorable nutrient availability. In outer reef waters, diatoms and green microalgae predominated whereas cyanobacteria and cryptophytes were nearly undetectable. Due to detrital decomposition and river discharge, the CDOM was much higher in the inner reef than in the outer reef. Benthic bluegreen microalgae were relatively more abundant in areas close to the river mouth and coastal agricultural fields. At these locations, nutrient concentrations were much higher due to river discharge and potentially significant groundwater discharge. Thus, phytoplankton and benthic microalgae can serve as indicators of terrestrial influence on coral reefs.

Spatiotemporal Patterns of Subtidal Benthic Microalgal Biomass and Community Composition in Galveston Bay, Texas, USA

Many Gulf of Mexico estuaries have low ratios of water volume to bottom surface area, and benthic processes in these systems likely have a major influence on system structure and function. The purpose of this study was to determine the spatiotemporal distribution of biomass and community composition of subtidal benthic microalgal (BMA) communities in Galveston Bay, TX, USA, compare BMA community composition and biomass to phytoplankton in overlying waters, and estimate the potential contribution of BMA to the trophodynamics in this shallow, turbid, subtropical estuary. The estimates of BMA biomass (mean = 4.21 mg Chl a m−2) for Galveston Bay were within the range of the reported values for similar Gulf of Mexico estuaries. BMA biomass in the central part of the bay was essentially homogeneous, whereas biomass at the seaward and upper bay ends of the transect were significantly lower. Peridinin, fucoxanthin, and alloxanthin were the three carotenoids with the highest concentrations, with fucoxanthin having the highest mean concentration (1.82 mg m−2). The seaward and landward ends of the transect differed from the central region of the bay with respect to the relative abundances of chlorophytes, cyanobacteria, and photosynthetic bacteria. Benthic microalgal community composition also showed a gradual shift over time due to changes in the relative abundances of photosynthetic bacteria, cryptophytes, dinoflagellates, and cyanobacteria. Major changes in community composition occurred in the spring months (March to April). On an areal basis, BMA biomass in Galveston Bay occurred at minor concentrations (16.5%) relative to phytoplankton. Furthermore, the concentrations of carotenoid pigments for phytoplankton and BMA (fucoxanthin, alloxanthin, and zeaxanthin) were correlated (r = 0.48 to 0.61), suggesting a close linkage between microalgae in the water column and sediments. The contribution of BMA to the primary productivity of the deeper waters (>2 m) of Galveston Bay is probably very small in comparison to shallower waters along the bay margins. The significant similarities in the community composition of phytoplankton and BMA illustrate the potential importance of deposition and resuspension processes in this turbid, shallow estuary.

Lotic biofilm community structure and pesticide tolerance along a contamination gradient in a vineyard area

We investigated the environmental impact of diffuse pesticide pollution on natural river biofilms in the River Morcille, France, during 2 seasons in pristine and contaminated stations. Prokaryotic and eukaryotic community compositions were assessed by denaturing gradient gel electrophoresis, while microalgal community composition was determined by high pressure liquid chromatography pigment analysis. The sensitivity of microphytobenthos to the herbicide Diuron was investigated in the laboratory by short-term photosynthesis inhibition assays. Spatial changes in prokaryotic and eukaryotic species compositions were found in spring and in winter. Community structures were significantly different between contaminated areas and those that were uncontami- nated or less contaminated. Associated changes in biodiversity were not found. Community tolerance towards Diuron (based on EC50 values for photosynthesis) was significantly lower in upstream than in downstream photoautotrophic organisms. Pesticide concentration increased along the downstream gradient. These results strongly suggest contamination-driven changes in biofilm community struc- ture and in the tolerance of the photoautotrophic community, confirming the Pollution-Induced Community Tolerance (PICT) hypothesis.

REGULATION OF BENTHIC ALGAL AND ANIMAL COMMUNITIES BY SALT MARSH PLANTS: IMPACT OF SHADING

Plant cover is a fundamental feature of many coastal marine and terrestrial systems and controls the structure of associated animal communities. Both natural and human-mediated changes in plant cover influence abiotic sediment properties and thus have cascading impacts on the biotic community. Using clipping (structural) and light (shading) manipulations in two salt marsh vegetation zones (one dominated by Spartina foliosa and one by Salicornia virginica), we tested whether these plant species exert influence on abiotic environmental factors and examined the mechanisms by which these changes regulate the biotic community. In an unshaded (plant and shade removal) treatment, marsh soils exhibited harsher physical properties, a microalgal community composition shift toward increased diatom dominance, and altered macrofaunal community composition with lower species richness, a larger proportion of insect larvae, and a smaller proportion of annelids, crustaceans, and oligochaetes compared to shaded (plant removal, shade mimic) and control treatment plots. Overall, the shaded treatment plots were similar to the controls. Plant cover removal also resulted in parallel shifts in microalgal and macrofaunal isotopic signatures of the most dynamic species. This suggests that animal responses are seen mainly among microalgae grazers and may be mediated by plant modification of microalgae. Results of these experiments demonstrate how light reduction by the vascular plant canopy can control salt marsh sediment communities in an arid climate. This research facilitates understanding of sequential consequences of changing salt marsh plant cover associated with climate or sea level change, habitat degradation, marsh restoration, or plant invasion.

Effects of the density of an invasive crayfish (Procambarus clarkii) on pelagic and surface microalgae in a Mediterranean wetland

To understand the relationship between the density of an introduced crayfish species (P. clarkii) and the abundance and composition of pelagic and surface microalgae (hereafter referred to as phytoplankton and phytoneuston, respectively) we ran an in situ experiment in a Mediterranean wetland. In May 2004, we delimited six 10 x 7m areas along a channel in the Padule di Fucecchio (Italy). Each area was randomly chosen to host crayfish populations at either low (1 crayfish/m 2 ) or high densities (14 crayfish/m 2 ). Phytoplankton and phytoneuston samplings were conducted in August and in September 2004, corresponding to the periods in which the highest and the lowest numbers of free-moving crayfish were found, respectively, during the lentic phase of the water regime. Results showed that (1) phytoneuston biomass, composed of cyanobacteria and, to a lesser extent, of euglenoids, was strongly affected by the presence of dense populations of P. clarkii in August; (2) crayfish seemed to modify the composition of microalgal communities; (3) these effects were not accompanied by significant differences between experimental areas in water chemistry and temperature; (4) physico-chemical measures highly varied with sampling periods along with a change in phytoplankton and phytoneuston abundance; and (5) high crayfish densities did not to exert any measurable effect on phytoplankton abundance. The decrease of phytoneuston may be the result of top-down effects of crayfish removing invertebrate grazers or, most likely, of direct grazing of crayfish. Indeed, crayfish were often observed climbing on macrophytes and feeding on the floating film.

Meridional distribution of arsenic species in the subantarctic zone of the Southern Ocean, south of Australia

Distribution of the arsenic species total inorganic arsenic [As(V+III)], arsenite [As(III)], monomethyl arsenic (MMA), and dimethyl arsenic (DMA) was studied in the Subantarctic Zone (SAZ) of the Southern Ocean, south of Australia, during the austral autumn (March 1998). As(V) was the dominant arsenic species in both vertical profiles and surface waters along the meridional transect 42°–55°S, 141°30′E. It was also the only species observed at depths &gt;600 m. Concentrations of the reduced arsenic species (As(III), MMA, and DMA) were low in these waters compared with other oceanic sites with similar concentrations of chlorophyll a. As(III) concentrations could not be reliably quantified at any sites (&lt;0.04 nM). The greatest conversion of As(V) to “biological” species was found at the surface in the Subtropical Convergence Zone (2.5%) and decreased heading southward to 1% in the Polar Front (PF). While the decline in methyl arsenic concentrations was broadly associated with water temperature and measures of biological production, slightly different trends were found in the SAZ and PF. North of the Subantarctic Front (SAF), methyl arsenic concentrations were well correlated with water temperature, while south of the front, no such relation existed. In addition, the ratio DMA/MMA increased south of the SAF, associated with a change in the microalgal community composition. Low water temperature, phosphate‐replete conditions, and low biological productivity in the Southern Ocean all contribute to the concentrations of biologically produced arsenic species in this region being among the lowest reported for oceanic waters.

Application of photopigment biomarkers for quantifying microalgal community composition and in situ growth rates

In estuarine waters, phytoplankton are exposed to rapidly changing conditions that may affect community structure and function. In this study we determined the effects of mixing, turbidity, and limiting nutrient (N) additions on natural phytoplankton growth rates and algal group-specific biomass changes. Mesocosm bioassays were used to quantify the short-term (2–3 day) responses of phytoplankton from the Neuse river estuary, NC. Growth rates were higher under static conditions in N-amended tanks, while biomass of most algal groups was higher under mixed, turbid conditions with N additions. Shifts in community composition did not follow any consistent pattern but each factor influenced phytoplankton growth, biomass, and community composition. Differing growth responses to nutrient additions, mixing, and turbidity resulted in taxonomically-distinct communities. These results highlight the complexity of phytoplankton community structuring processes in estuarine waters. The combination of biomarker quantifications and the radiolabeling method is a useful tool for assessing phytoplankton responses and offers insights into the mechanisms driving blooms and bloom species in estuarine waters.

Fatty acid, sterol and hydrocarbon composition of Antarctic sea ice diatom communities during the spring bloom in McMurdo Sound

The lipid composition of microalgal communities dominated by diatoms collected from the sea ice at three locations within McMurdo Sound during the austral spring bloom of 1989/90, was determined using gas chromatography (GC) and GC mass spectrometry. A range of C27-C29 sterols were detected. The major sterols found at the three sites were 24-methylcholesta-5, 22E-diene-3β-ol (Cape Armitage); trans-22-dehydrocholesterol, 24-ethylcholesterol and 24-methylenecholesta (Erebus Ice Tongue); and 24-methylenecholesterol (Cape Royds). The difference in sterol profiles is believed to reflect the differing species composition at each site. The high relative levels (as % of total) of 24-ethylcholesterol at the Erebus Ice Tongue site (possibly related to Amphiprora kufferathii) supports the proposal that diatoms are a more probable source of C29 sterols in Antarctic lakes than are other algal groups or cyanobacteria. Changes in sterol composition over the course of the bloom were evident at the Cape Armitage site, particularly within the cellular free-lipid fraction. The major fatty acids identified were 14:0, 16:0, 16:1ω7c, 16:4ω1 and 20:5ω3 (Cape Armitage and Erebus Ice tongue sites); 16:0, 16:1ω7c and 20:5ω3 (Cape Royds site). All sites demonstrated high levels of PUFA (40–50% of total fatty acids), with an average 20:5ω3 level of 21% Erebus Ice Tongue, 20% Cape Royds, and 17% Cape Armitage. Variation was also observed in the percentage of 20:5ω3 for the Cape Armitage community over the sampling period. Levels of 22:6ω3 were between 0.4 and 1% of total fatty acids for the three sites. A C25:2 isoprenoid hydrocarbon was present in samples from all sites, adding further evidence to the proposal that diatoms are probably a source of this and related isoprenoid alkenes in marine and coastal sediments.

Primary Colonization by Microalgae in Relation to Spatial Variation in Edaphic Factors on Antarctic Fellfield Soils

1. The causes of variations in the composition of microalgal communities on frost-sorted soil polygons on Signy Island, maritime Antarctica, were investigated, based on analyses of physical and chemical conditions and microalgal communities from 65 polygons. 2. Interpolygon variations in all environmental factors measured were small and not much greater than the intrapolygon variations. Microalgal diversity was low. Only seven taxa occurred in sufficient numbers to be included in statistical analyses, two of which, Nostoc spp., were found on only one polygon. The filamentous cyanobacterium Phormidium autumnale occurred on all polygons and usually provided the largest component of the total biovolume. 3. Microalgal communities were qualitatively constant within polygons, but varied markedly between polygons. Principal components analysis indicated that each taxon varied independently of the others, and hence it was not possible to correlate community structure with any specific environmental factor. 4. Correlations between numbers of individual taxa and edaphic factors were low and accounted for a maximum of 18% of the observed interpolygon variation or 12% of the total variation. It is suggested that the observed differences in the microalgal communities were due to the vagaries of the colonization process and reflect the probability of successful colonization of these ecosystems by microalgae.