Late Holocene changes in cyanobacterial community structure in maritime Antarctic lakes

in Journal of Paleolimnology (2013), 50

Despite the dominance of cyanobacteria in polar freshwater aquatic ecosystems, little is known about their past biodiversity and response to climate and environmental changes. We explored the use of light ... [more ▼]

Despite the dominance of cyanobacteria in polar freshwater aquatic ecosystems, little is known about their past biodiversity and response to climate and environmental changes. We explored the use of light microscopy of microfossils, high performance liquid chromatography of the fossil pigment composition and denaturing gradient gel electrophoresis of fossil 16S rRNA genes to study past and present-day differences in cyanobacterial community structure in response to climate changes in two adjacent maritime Antarctic lakes with contrasting depths (4 and 26 m) and light climates. Light microscopy was of limited use because of degradation of cell structures. Fossil cyanobacterial pigment concentrations were below the detection limits of our method in several sediment samples in the deep lake, but abundant and diverse inthe sediment core from the shallow pond, probably as a consequence of increased light availability and/or a more diverse and abundant benthic cyanobacterial flora. Total carotenoid and chlorophyll concentrations were highest in both lakes between ca. 2,950 and 1,800 cal yr BP, which coincides with the late Holocene climate optimum recognised elsewhere in maritime Antarctica. Cyanobacterial molecular diversity was higher in the top few centimeters of the sediments in both lakes. In deeper sediments, the taxonomic turnover of cyanobacteria appeared to be relatively small in response to past climate anomalies in both lakes, underscoring the broad tolerance of cyanobacteria to environmental variability. This, however, may in part be explained by the low taxonomic resolution obtained with the relatively conserved 16S rRNA gene and/or the preferential preservation of particular taxa. Our results highlight the potential of fossil DNA in lake sediments to study colonization and succession dynamics of lacustrine cyanobacteria and warrant further investigation of the factors that affect preservation of cyanobacterial DNA. [less ▲]

Antarctic Microbial BIOdiversity : the importance of geographical versus ecological factors

Poster (2012, July)

Antarctica is a prime region to test whether microbes have a biogeography and to study their metacommunity dynamics, because (i) it is isolated from the other continents, (ii) its extreme environmental ... [more ▼]

Antarctica is a prime region to test whether microbes have a biogeography and to study their metacommunity dynamics, because (i) it is isolated from the other continents, (ii) its extreme environmental conditions allow microorganisms to dominate its ecosystems, and (iii) lacustrine and terrestrial habitats occur isolated in a matrix of ice and ocean. We compiled a large set of samples from benthic microbial mats from Antarctic lakes in different ice-free regions and used a polyphasic approach to study their microbial biodiversity by combining morphological characterization of diatoms with molecular techniques such as Denaturing Gradient Gel Electrophoresis (green algae and cyanobacteria), 454 pyrosequencing and cultivation (prokaryotes). [less ▲]

Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006–2008)

in Progress in Oceanography (2012), 114

We determined the spatial and temporal dynamics of major phytoplankton groups in relation to biogeochemical and physical variables during the late spring coccolithophore blooms (May-June) along and across ... [more ▼]

We determined the spatial and temporal dynamics of major phytoplankton groups in relation to biogeochemical and physical variables during the late spring coccolithophore blooms (May-June) along and across the continental margin of the northern Bay of Biscay (2006-2008). Photosynthetic biomass (Chla) of the dominant plankton groups was determined by CHEMTAX analysis of HPLC pigment signatures. We used uni- and multivariate statistical techniques to identify the main physical and biogeochemical variables underlying the variation in phytoplankton biomass and community structure. Phytoplankton standing stock biomass varied substantially between and during the campaigns (areal Chla (mg Chla m-2) in June 2006: 63.8 ± 26.5, May 2007: 27.9 ± 8.4, and May 2008: 41.3 ± 21.8), reflecting the different prevailing weather, irradiance, and sea surface temperature conditions between the campaigns. Coccolithophores, represented mainly by Emiliania huxleyi, and diatoms were the dominant phytoplankton groups, with a maximal contribution of, respectively, 72% and 89% of the total Chla. Prasinophytes, dinoflagellates, and chrysophytes often co-occurred during coccolithophorid blooms, while diatoms dominated the phytoplankton biomass independently of the abundance of other groups. The location of the stations on the shelf or on the slope side of the continental margin did not influence the biomass and the composition of the phytoplankton community despite significantly stronger water column stratification and lower nutrient concentrations on the shelf. The alternation between diatom and coccolithophorid blooms of similar biomasses, following the mostly diatom-dominated main spring bloom, was partly driven by changes in nutrient stoichiometry (N:P and dSi:N). High concentrations of transparent exopolymer particles (TEP) were associated with stratified, coccolithophore-rich water masses, which probably originated from the slope of the continental margin and warmed during advection onto the shelf. Although we did not determine the proportion of export production attributed to phytoplankton groups, the abundance of coccolithophores, TEP, and coccoliths may affect the carbon export efficiency through increased sinking rates of particles formed by aggregation of TEP and coccoliths. [less ▲]

The limnology and biology of the Dufek Massif, Transantarctic Mountains 82° South

in Polar Science (2010), 4

Very little is known about the higher latitude inland biology of continental Antarctica. In this paper we describe the limnology and biology of the Dufek Massif, using a range of observational ... [more ▼]

Very little is known about the higher latitude inland biology of continental Antarctica. In this paper we describe the limnology and biology of the Dufek Massif, using a range of observational, microscopic and molecular methods. Here two dry valleys are home to some of the southernmost biota on Earth. Cyanobacteria were the dominant life forms, being found in lakes and ponds, in hypersaline brines, summer melt water, relict pond beds and in exposed terrestrial habitats. Their species diversity was the lowest yet observed in Antarctic lakes. Green algae, cercozoa and bacteria were present, but diatoms were absent except for a single valve; likely windblown. Mosses were absent and only one lichen specimen was found. The Metazoa included three microbivorous tardigrades (Acutuncus antarcticus, Diphascon sanae and Echiniscus (cf) pseudowendti) and bdelloid rotifer species, but no arthropods or nematodes. These simple faunal and floral communities are missing most of the elements normally present at lower latitudes in the Antarctic which is probably a result of the very harsh environmental conditions in the area. [less ▲]

Structuring effects of climate-related environmental factors on Antarctic microbial mat communities

in Aquatic Microbial Ecology (2010), 59

Both ground-based and satellite data show that parts of Antarctica have entered a period of rapid climate change, which already affects the functioning and productivity of limnetic ecosystems. To predict ... [more ▼]

Both ground-based and satellite data show that parts of Antarctica have entered a period of rapid climate change, which already affects the functioning and productivity of limnetic ecosystems. To predict the consequences of future climate anomalies for lacustrine microbial communities, we not only need better baseline information on their biodiversity but also on the climaterelated environmental factors structuring these communities. Here we applied denaturing gradient gel electrophoresis (DGGE) of the small subunit ribosomal DNA (SSU rDNA) to assess the genetic composition and distribution of Cyanobacteria and eukaryotes in 37 benthic microbial mat samples from east Antarctic lakes. The lakes were selected to span a wide range of environmental gradients governed by differences in lake morphology and chemical limnology across 5 ice-free oases. Sequence analysis of selected DGGE bands revealed a high degree of potential endemism among the Cyanobacteria (mainly represented by Oscillatoriales and Nostocales), and the presence of a variety of protists (alveolates, stramenopiles and green algae), fungi, tardigrades and nematodes, which corroborates previous microscopy-based observations. Variation partitioning analyses revealed that the microbial mat community structure is largely regulated by both geographical and local environmental factors of which salinity (and related variables), lake water depth and nutrient concentrations are of major importance. These 3 groups of environmental variables have previously been shown to change drastically in Antarctica in response to climate change. Together, these results have obvious consequences for predicting the trajectory of biodiversity under changing climate conditions and call for the continued assessment of the biodiversity of these unique ecosystems. [less ▲]

Coccolithophore bloom dynamics shape bacterioplankton communities in the northern Bay of Biscay

Poster (2008, August 17)

Coccolithophores (Prymnesiophyceae) such as Emiliania huxleyi belong to the most productive calcifying organisms in the oceans. During two consecutive years we assessed bacterial diversity and dynamics ... [more ▼]

Coccolithophores (Prymnesiophyceae) such as Emiliania huxleyi belong to the most productive calcifying organisms in the oceans. During two consecutive years we assessed bacterial diversity and dynamics during the course of spring phytoplankton blooms dominated by coccolithophores in the northern part of the Bay of Biscay. Bacterioplankton community composition was assessed by means of denaturing gradient gel electrophoresis (DGGE) in combination with 16S rRNA gene clone libraries. We used ordination analysis to relate bacterioplankton community dynamics to phytoplankton pigment data and environmental parameters (nutrient concentrations, total alkalinity, concentration of transparent exopolymeric particles (TEP), pCO2). We found a clear difference in composition between the free-living and the particle-associated bacterial assemblage, with the identified Flavobacteria and Sphingobacteria phylotypes being characteristic for the particle-associated bacterial assemblage and Alfaproteobacteria and members of the SAR86 cluster dominating the free-living bacterial assemblage. Stations along the continental margin, at different stages in the coccolithophore bloom, were characterized by distinct bacterial assemblages which correlated well with changes in phytoplankton community composition and TEP abundance. We hypothesize that coccolithophore bloom dynamics shape both the free-living and the particle associated bacterial assemblages through phytoplankton group-specific associations and TEP production [less ▲]

Covariation between zooplankton community composition and cyanobacterial community dynamics in Lake Blaarmeersen (Belgium)

in FEMS Microbiology Ecology (2008), 63

The cyanobacterial community composition in the mesotrophic Lake Blaarmeersen was determined by denaturing gradient gel electrophoresis (DGGE) of PCRamplified 16S rRNA gene fragments during two ... [more ▼]

The cyanobacterial community composition in the mesotrophic Lake Blaarmeersen was determined by denaturing gradient gel electrophoresis (DGGE) of PCRamplified 16S rRNA gene fragments during two consecutive years to assess the importance of different classes of explanatory variables (bottom-up and top-down factors, physical variables and phytoplankton) in cyanobacterial community dynamics. The most dominant cyanobacteria in Lake Blaarmeersen were Synechococcus (three genotypes), Limnothrix redekei and Anabaena/Aphanizomenon. Analyses of Similarity revealed that the cyanobacterial community in Lake Blaarmeersen differed significantly between the growing season and the winter season as well as between the epilimnion and hypolimnion during the stratified periods. Mantel tests revealed significant correlations between the DGGE data and bottom-up factors, physical variables, the phytoplankton community composition and, interestingly, the zooplankton community composition. In general, the zooplankton community composition (especially the cladoceran community) was more important in structuring the cyanobacterial community than the total zooplankton biomass. This study shows that grazing zooplankton communities can have a relatively strong impact on the cyanobacterial community dynamics and that this impact can be equally important as bottom-up processes regulated by nutrient concentrations and/or physical variables. [less ▲]

Ecological characteristic's of small farmland ponds: Associations with land use practices at multiple spatial scales

in Biological Conservation (2006), 131(4), 523-532

Despite their restricted surface area, small farmland ponds often have a high conservation value because they contribute significantly to regional biodiversity and contain rare or unique species. For this ... [more ▼]

Despite their restricted surface area, small farmland ponds often have a high conservation value because they contribute significantly to regional biodiversity and contain rare or unique species. For this reason, the creation of new ponds has become a widely applied practice in many countries. information on the effects of land use on farmland ponds is very scarce. Farmland ponds differ from larger ponds, lakes and livers in many aspects and can therefore be expected to be affected by land use via other mechanisms operating at different spatial scales. We here present a study on 126 ponds distributed over the entire territory of Belgium (surface area: 30.500 km(2)). We assessed variables related to turbidity state and vegetation complexity and related them to land use variables assessed at several spatial scales ranging from the pond edge up to 32 km(2) circular areas. According to redundancy analysis, trampling by cattle and percentage cover of nearby crop land were positively associated with turbid state related variables. Conversely, ponds with high coverage by forest in the immediate neighbourhood tended to be more associated with the clear water state. Multiple regression analysis demonstrated a negative effect of trampling and coverage by crop land on vegetation complexity. Effects of crop lands and forest were strongest at the local scale (< 200 m radius) which indicates that adverse external influences can most efficiently be mitigated at a small scale. Based on these results we suggest several recommendations for pond construction and conservation. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]