Testate Amoeba Assemblages Research Articles

Analysis of fossil testate amoebae in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands

Niinemets, E., Pensa, M. & Charman, D. J. 2010: Analysis of fossil testate amoebae in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands. Boreas, 10.1111/j.1502-3885.2010.00188.x. ISSN 0300-9483. Local variability in decadal water-table changes on an ombrotrophic peatland was explored using testate amoebae analysis of near-surface peats in an Estonian raised bog. The distribution of testate amoebae assemblages was studied along the gradient from hummock to hollow in the upper 30-cm layer of peat. As expected, testate amoebae assemblages in different micro-ecotypes from hummock to hollow, even as close as 10 m apart, are distinctly different. Past water-table change was reconstructed by applying a transfer function based on modern samples from throughout Europe. Results show a decline in water level from the mid-late 20th century on Selisoo bog in all profiles from the different micro-ecotypes. However, the absolute water-table depths and amplitudes of fluctuations vary between reconstructions from different sampling micro-ecotypes. Cores were correlated using changes in non-mire pollen concentrations down-core, but it was not possible to correlate minor changes in water-table owing to non-contiguous sampling and variable accumulation rates. We conclude that different microtopes show the same decadal trends in relative water-table change but that the absolute magnitude of change may be more variable locally. It is important that reconstructed palaeohydrological changes in bogs consider changes in bog micro-ecotypes, and their variation over time, as this may alter the sensitivity of an individual record to drivers such as climate change. Comparison and compilation of data from parallel cores from different micro-ecotypes and/or different sites are likely to provide more robust reconstructions.

Climatic changes during the Lateglacial-Holocene transition as reflected by variations in testate amoeba assemblages at Lake Lautrey (Jura mountains, Eastern France)

L’analyse des assemblages de thecamoebiens (Protistes, Rhizopodes) au cours de la transition Tardiglaciaire-Holocene au lac du Lautrey (Jura) offre l’opportunite de tester la reponse de ces micro-organismes lacustres aux changements du climat et de l’environnement. Les donnees obtenues lors d’une precedente etude multi-parametres a haute resolution sur la meme sequence sedimentaire ont servi de base de reference pour les observations. Les premiers resultats montrent que les evenements climatiques majeurs successifs qui caracterisent la transition Tardiglaciaire-Holocene (c’est-a-dire le Dryas ancien, l’Interstade Bolling-Allerod, le Dryas recent, le Preboreal) correspondent a des changements dans la composition des assemblages de thecamoebiens (especes dominantes et structure des assemblages) ainsi que du taux d’accumulation des theques. Les refroidissements climatiques mineurs comme le Dryas moyen ou l’oscillation de Gerzensee sembleraient etre enregistres egalement, notamment par des diminutions du taux d’accumulation, excepte pour l’oscillation du Preboreal qui n’a pas ete mise en evidence alors qu’elle apparait bien caracterisee par d’autres indicateurs. Ce travail montre l’interet de l’utilisation des thecamoebiens pour les reconstitutions paleoclimatiques. Cependant, une meilleure comprehension des relations entre le climat et la composition des assemblages de thecamoebiens necessite encore 1) une meilleure resolution sur cette sequence du lac du Lautrey ainsi que la mise en oeuvre, sur d’autres sites, d’etudes similaires a haute resolution basees sur une approche pluridisciplinaire, et 2) la mise en place d’analogues modernes pour mieux cerner la signification paleoclimatique de ces micro-organismes.

Biogeographic variation in Thecamoebian ( Testate amoeba ) assemblages in lakes within various vegetation zones of Alberta, Canada

Thecamoebians (Testate amoebae) have proven to be valuable proxies commonly used in environmental and paleoenvironmental studies. A better understanding of their geographic distribution and environmental parameters influencing this distribution is required for further thecamoebian research. Thecamoebians were analyzed from twelve lakes spanning five drainage basins and four vegetation zones, representing a variety of environmental and limnological parameters in Alberta, Canada. Species diversity is low throughout the study sites, ranging from 1.35 to 2.17, with various strains of Difflugia oblonga, Centropyxis constricta and Centropyxis aculeata dominating the fauna. Climate, as reflected in the vegetation zones, appears to be an influencing factor on species and strain distributions. Low-diversity assemblages strongly dominated by C. aculeata and C. constricta,characterize lakes in the rocky mountain region. Slightly, more diverse assemblages dominated by D. oblonga and Cucurbitella tricuspis characterize lakes in the grassland region. The highest Thecamoebian diversity was found in both the Boreal Forest and Parkland zones. The Boreal Forest is dominated by D. oblonga together with C. constricta,C. tricuspis and C. aculeata, while the Boreal Parkland is dominated by D. oblonga along with C. constricta and C. aculeata. Key words: Thecamoebians, Testate amoebae, Biogeographic, Alberta

Response of testate amoeba assemblages to environmental and climatic changes during the Lateglacial–Holocene transition at Lake Lautrey (Jura Mountains, eastern France)

AbstractWe tested the response of lacustrine testate amoebae (thecamoebians) to climate and environmental changes for the Lateglacial–Holocene transition. The palaeoenvironmental history of the study site (Lake Lautrey, Jura Mountains, eastern France) was previously established based on high‐resolution multi‐proxy studies of the same core. The present study is characterised by a high taxonomic resolution (54 taxa), inclusion of small species (down to 25 µm) and high total counts (>500 individuals per sample on average). Changes in the composition of testate amoeba assemblages (dominant species and assemblage structure), as well as in the accumulation rate (tests cm−2 a−1), corresponded to major climatic phases (i.e. Oldest Dryas, Bølling–Allerød Interstadial, Younger Dryas, Preboreal) as well as changes in organic matter inputs. Furthermore, decreases in the accumulation rate characterised minor short‐lived cooling events, such as Older Dryas event or Gerzensee oscillation. However, the Preboreal oscillation, which was well registered by other proxies at Lake Lautrey, could not be recognised in the testate amoeba record. This work demonstrates that lacustrine testate amoebae can be used for palaeoclimatic and palaeoecological reconstructions. Nevertheless, a better understanding of the relation between climate, organic matter and lacustrine testate amoebae requires further high‐resolution studies based on multi‐proxy approaches and the development of appropriate modern analogues. Copyright © 2010 John Wiley & Sons, Ltd.

Does Climate Warming Stimulate or Inhibit Soil Protist Communities? A Test on Testate Amoebae in High-Arctic Tundra with Free-Air Temperature Increase

Soil testate amoebae assemblages in a grassland area at Zackenberg (Northeast Greenland) were subjected to simulated climate-warming during the growing season using the Free-Air Temperature Increase technique. Samples were collected in upper (0 - 3cm) and deeper (3 - 6cm) soil horizons. Mean temperature elevations at 2.5 and 7.5cm depth were 2.58 ± SD 1.11 and 2.13±SD 0.77°C, respectively, and did not differ significantly. Soil moisture in the top 11cm was not affected by the warming. During the manipulation, the densities of living amoebae and empty shells were higher in the experimental plots but only in the upper layer. Possibly, testate amoebae in the deeper layer were limited by other factors, suggesting that warming enhances the carrying capacity only in favourable conditions. Species richness, on the other hand, was only increased in the deeper horizon. Warming did not change the percentage of individuals belonging to small-sized species in any of the living assemblages, contrary to our expectation that those species would quickly increase their density. However, in the empty shell assemblages, the proportion of small-sized individuals in the experimental plots was higher in both layers, indicating a rapid, transient increase in small amoebae before the first sampling date. Changes in successional state of testate amoebae assemblages in response to future climate change might thus be ephemeral, whereas alterations in density and species richness might be more sustained.

Influence of sediment grain size and mineralogy on testate amoebae test construction

Testate amoebae are increasingly used for environmental monitoring as well as paleoenvironmental reconstructions. Paleoecological interpretations of testate amoebae assemblages depend on the understanding of the ecological processes operating today. We then ask the question of the link between testate structure and its environment. This study analyses both the grain size and mineralogical assemblage of tests of common species belonging to the genus Centropyxis and Difflugia. It is concluded that grain size is a limiting factor for test construction, whereas mineral composition is not. Hence, when analyzing agglutinated testate amoebae for paleoenvironmental reconstructions, it should be taken into account the mean grain size of the sediment. A non-appropriate grain-size probably inhibits the development of a testate amoebae specific assemblage.

Surface wetness and mire development during the late Holocene in central Sweden

The aim of this thesis was to reconstruct humidity variability in central Sweden during the late Holocene. A multi-proxy approach was used to infer humidity changes as recorded in a lake and a mire. Age-models were constructed based on radiocarbon dating and the Askja-1875 tephra. Stable isotopes (δ18O and δ13C) on Chara spp encrustations and Pisidium spp mollusc shells and carbon content were analysed in the lake record, whereas peat stratigraphy, humification, testate amoebae assemblages, C/N ratio and stable isotopes (δ13C and δ15N) were analysed in the mire record. Stable isotopes (δ2H and δ18O) on lake water showed that Lake Blektjarnen responded to changes in the balance between evaporation and input water (E/I ratio). A high E/I ratio results from a dry and probably warmer climate during which evaporation and atmospheric equilibration likely enrich lake water in 18O and 13C, respectively, and vice versa for a low E/I ratio. The relatively high Chara δ18O and δ13C values between ca 4400 and 4000 cal yr BP thus suggest relatively dry and likely warm conditions, whereas depleted values suggest wetter and probably cooler conditions between ca 4000 and 3000 cal yr BP. Again, drier and probably warmer conditions were inferred from the relatively enriched δ18O values between ca 2500 and 1000 cal yr BP, and depleted δ18O values were recorded between ca 1000 and 50 cal yr BP indicating wetter and likely cooler conditions. The results from the mire mainly indicated vegetation succession, however, the changes inferred at ca 2600 and 1000 cal yr BP could have been triggered by climate change. This study shows that the proxies responded sensitively to humidity changes in the investigated archives allowing for reconstruction of climate change in central Sweden during late Holocene.

Relationships between Testate Amoebae Assemblages (Protozoa) and Geographic Factors in Yunnan Plateau Lakes, China

ABSTRACT Knowledge of the effect of geographic factors on the assemblages of protozoan testate amoebae is still limited, despite there having been a number of studies on this fauna. We applied statistical analyses to data on the distribution of testate amoebae from nine major lakes in the Yunnan Plateau, southwest China. Cluster analysis, based on community structure, separated the lakes into two groups—the ligotrophic/mesotrophic lakes and the hypereutrophic lakes—confirming the idea that the testate amoebae assemblages in lakes are closely related to the trophic status. Additionally, within the oligotrophic/mesotrophic lakes, there was distinct geographic clustering. Linear regression analysis and the Mantel test both revealed that similarity of species composition decreased with increasing geographic distance among the oligotrophic/mesotrophic lakes.

A preliminary investigation into the use of testate amoebae for the discrimination of forensic soil samples

We present the results of an initial investigation into the efficacy of using testate amoebae for the discrimination of soils from wet ground and puddles, as little attention has been given to these organisms in forensic science. The preservation of testate amoebae in these sediments is generally good, although test concentrations are low. Statistical analysis suggests that testate amoebae assemblages are somewhat spatially distinct and have potential to be used for soil discrimination. A case study is presented where mineralogical (X-ray diffraction) and testate amoebae analyses are used in conjunction to clarify the scene of crime in a 'cold case' murder enquiry. Testate amoebae were recovered from dried sediment residues on clothing 10 years after the murder. Despite these promising results, further experimental work is crucial to examine the spatial and temporal variation of amoebae assemblages in water films, wet ground and puddles before they can be added to the armoury of methods available to the forensic biologist.

Distal volcanic impacts on peatlands: palaeoecological evidence from Alaska

Despite the fact that volcanic ash (tephra) layers are found preserved in peat deposits around the world, comparatively little research has investigated the impacts of distal volcanic emissions on peatlands. This study investigates the impacts of several late-Holocene volcanic eruptions on five peatlands in southern Alaska using a palaeoecological approach. Testate amoebae analysis, peat humification analysis and a basic analysis of plant macrofossil components were applied across 11 tephra layers. Changes in macrofossil and testate amoebae assemblages occur across several of the tephra layers. The humification results were considered unreliable because of a methodological problem, a finding which may have implications for other studies using this technique. Redundancy analyses on testate amoebae data show statistically significant changes associated with two tephras. The most likely causes of the impacts are volcanic gases, acidic precipitation or tephra-derived leachates. The finding that some tephras are associated with impacts whereas others are not may relate to the season of the eruption or meteorological conditions at the time of ash fall. These results suggest the sensitivity of peatlands and peatland microbial communities to distal volcanic products and imply that changes in key palaeoclimatic proxies may be caused by a mechanism independent of climate change. Implications of the results for peat-based palaeoclimatic studies are discussed, as are possible directions for future research.

Vegetation history and human impact during the last 300 years recorded in a German peat deposit

A peat core from the Barschpfuhl kettlehole mire in north-east Germany was analysed for multiproxy indicators (plant macrofossils, pollen/non-pollen microfossils, testate amoebae, colorimetric humification, carbon/nitrogen ratios, bulk density, loss on ignition), to investigate the effects of climate change and human impact on vegetation and peat accumulation during the last c. 300 years. 14C wiggle-match dating was applied for high-precision dating. Testate amoebae assemblages were used to reconstruct past water table depths and compared with other proxies and instrumental climate data from the mid-18th century onwards. The mire hydrology of this relatively small bog was heavily influenced by forestry changes in the area. The climate signal was therefore obscured. Afforestation with fast-growing conifers and drainage for agricultural purposes resulted in a lowering of the water level, changes in trophic status, changes in mire surface vegetation and increased decomposition of the peat. Variations in the openness and cultivated land indicators in the pollen data of Barschpfuhl reflect regional population density and land use changes.

Effects of human impact and climate change during the last 350 years recorded in a Swedish raised bog deposit

A peat core from an ombrotrophic mire in central Sweden was analysed for multi-proxy indicators (plant macrofossils, pollen/non-pollen microfossils, testate amoebae, colorimetric humification, carbon/nitrogen ratios, bulk densities, loss on ignition), to evaluate the relative contributions of climate change and human impact on vegetation and peat accumulation during the last c. 350 years. 14C wiggle-match dating was applied for high precision dating. Testate amoebae assemblages were used to reconstruct past water table depths and compared with other proxies and instrumental climate data from the mid-18th century onwards. Changes in mire surface wetness were mainly caused by climate change (precipitation and evaporation), but the internal dynamics of the local bog vegetation may also have played a role in the recorded water table changes. The human impact signal in the pollen data was compared with Swedish population and land-use data. A link between climate change, human impact (openness of the vegetation) and demographic change was found. Cold and wet periods show a decrease in human impact and open land indicators in the pollen data, followed by an increase in death rate and/or an increase in emigration.

Testate amoebae as proxies for mean annual water‐table depth in Sphagnum‐dominated peatlands of North America

AbstractPeatland‐inhabiting testate amoebae are sensitive indicators of substrate‐moisture conditions and have increasingly been used in palaeohydrological studies. However, to improve accuracy of testate‐amoeba‐based hydrological inferences, baseline ecological data on rare taxa, a larger geographic network of calibration sites, and incorporation of long‐term estimates of water‐table depth are needed. Species–environment relationships at 369 sites from 31 peatlands in eastern North America were investigated. Long‐term estimates of water‐table depth were obtained using the method of polyvinyl (PVC) tape‐discolouration. Transfer functions were developed using a variety of models, and validated through jackknifing techniques and with an independent dataset where water‐table depths were directly measured throughout the growing season. Results indicate that mean annual water‐table depth can be inferred from testate amoeba assemblages with a mean error of 6 to 8 cm, although there is a slight systematic bias. All transfer function models performed similarly and produced similar reconstructions on a fossil sequence. In a preliminary effort towards development of a comprehensive North American calibration dataset, data from this study were combined with previous studies in Michigan and the Rocky Mountains (n = 650). This combined dataset had slightly larger mean errors of prediction (8–9 cm) but includes data for several rare taxa. Copyright © 2007 John Wiley & Sons, Ltd.

Increased aeolian activity during humidity shifts as recorded in a raised bog in south-west Sweden during the past 1700 years

Abstract. Analyses of testate amoebae and aeolian sediment influx (ASI) were used to reconstruct effective humidity changes and aeolian activity in the coastal zone of south-west Sweden. Cores were taken from an ombrotrophic peat sequence from the Undarsmosse bog. Since both types of analysis were carried out on the same core, a direct comparison between humidity fluctuations in the bog and aeolian activity was possible, potentially providing detailed information on atmospheric circulation changes in this region. Relatively wet bog surface conditions occurred from around 1500 to 1230 and 770 to 380 cal. yrs BP, whereas dry conditions dominated from ca. 1630 to 1530, 1160 to 830 and 300 to 50 cal. yrs BP. The transitions between these phases occurred within 60–100 years and are characterised by a major change in the testate amoebae assemblages. A watertable reconstruction was used to study the hydrological changes at the bog surface in more detail. ASI peak events were reconstructed around 1450, 1150, 850 and after 370 cal. yrs BP. Most interestingly, these aeolian activity peaks started during the recorded hydrological transitions, regardless of the direction of these shifts. Our results therefore suggest that humidity shifts in this region were associated with temporary intensifications of atmospheric circulation during the past 1700 years. Several ASI peaks apparently coincide with reduced solar activity, possibly suggesting a solar related cause for some of the observed events.

Reconstructing hydrological variability from testate amoebae analysis in Carpathian peatlands

Peatlands offer the potential for high resolution records of water balance over Holocene timescales, yet this potential is under-exploited in many areas of the world. Within Europe, peatlands are mostly confined to areas north of 55° N, but several areas of southern and eastern Europe contain small peatlands which may be suitable for palaeoclimatic reconstruction. In this paper we test the potential of peatlands in the Carpathian region for deriving quantified estimates of water table changes using testate amoebae analysis. A training set for palaeohydrological reconstruction from testate amoebae assemblages was obtained by collecting surface samples from 13 peatlands, including 9 from Hungary and 4 from Transylvania (Romania). Using a simple measure of mean annual water tables estimated from staining of PVC tape, we found that some peatlands were heavily influenced by runoff and groundwater, and were therefore not suitable as modern analogues of ombrotrophic climatically sensitive sites. The relationship between the testate amoebae assemblages in the modern samples and the environmental variables was explored using CCA. The CCA biplot showed that the most important variables are depth to water table and moisture content, confirming that hydrology is a key control on taxon distribution. pH was a secondary gradient. A transfer function for % moisture and depth to water table was established and applied to fossil assemblages from a sequence from Fenyves-tető, Transylvania, Romania. The reconstructed water table shows a number of variations which have parallels with other palaeoclimatic records from Europe and the North Atlantic prominent phases of higher water tables are associated with the periods 8000–8300 cal BP, 3000–2500 cal BP and after 600 cal BP. We suggest that these were periods of particular intensification of westerly airflow which affected eastern Europe as well as western and central Europe.

A comparative study of peat proxies from two eastern central Swedish bogs and their relation to meteorological data

AbstractAnalyses of peat humification, testate amoebae, carbon and nitrogen content have been carried out on a peat sequence from Ältabergsmossen. At Gullbergbymossen testate amoebae and peat humification were analysed. Both bogs are located in eastern central Sweden. The longest sequence, Ältabergsmossen, covers the last 150 yr and the data from Gullbergbymossen covers the last 60 yr, both with a time resolution of ca. 2–4 yr cm−1. The different proxies were compared to each other and were also compared to instrumental meteorological data. Correlation between peat humification and C/N ratios is high whereas the correlation is low between these physical/chemical parameters and reconstructed water tables inferred from the testate amoebae assemblages. High peat humification values and C/N ratios greater than 50 indicate aerobic decay and are thought to reflect the thickness of the acrotelm. High humification values and low C/N ratios are recorded in peat deposited between 1965 and 1980, whereas the dry period starts in the early 1970s according to instrumental meteorological data and inferred water‐table depth. The difference in the timing of the onset of a dry‐shift between the physical/chemical proxies and meteorological data and testate amoebae derived water table changes is interpreted as renewed decay of already deposited peat. The term secondary decomposition is used for this process. The secondary decomposition process has implications for interpreting physical/chemical and biological parameters in peat as they may be out of phase during the beginning of a dry‐shift. Copyright © 2005 John Wiley & Sons, Ltd.

Reconstructed water tables from two ombrotrophic mires in eastern central Sweden compared with instrumental meteorological data

Water-level changes for the last 125 years were reconstructed from two ombrotrophic mires in eastern central Sweden using testate amoebae assemblages. The reconstructed water tables show the same overall pattem with high water tables during the 1950s and 1960s and low water levels from the 1970s until present. The similarity in the two records supports the hypothesis that water-table changes in the ombrotrophic mires of this area are driven by climate change. Correlation of decadal means of reconstructed iV l water levels and instrumental meteorological data was performed to examine the relationship between water table and climatic variability. The results show that the reconstructed water tables are correlated with changes in mean annual temperature (p < 0.05). This contrasts with similar data for other parts of Europe where correlations have been found with summer or annual precipitation and temperature. We A suggest that low rainfall in this area of Sweden makes the peatlands more susceptible to changing temperaHOLOCENE ture and that the lack of a response to precipitation is a function of low rainfall variability over the comRESEARCH parison period. The results show that mire surface wetness responses to climate change are spatially PAPER variable and greater attention should be given to understanding this variability if more accurate palaeoclimatic inferences are to be drawn from longer Holocene records.

Freshwater Testate Amoebae Communities from Île de la Possession, Crozet Archipelago, Subantarctica

An ecological study of the freshwater testate amoebae (Protozoa, Rhizopoda) on the subantarctic island Île de la Possession (Crozet Archipelago) revealed 85 taxa, belonging to 21 genera. Twenty-two taxa belonged to the genus Difflugia, typical for freshwater habitats whereas the genus Trinema showed the highest relative abundance. A cluster analysis revealed two communities: a Difflugiella crenulata assemblage and a Trinema lineare–T. enchelys assemblage. These communities, together with the results of a RDA analysis, represented a clear geographical separation on the island. The Difflugiella crenulata assemblage typified locations, with a high specific conductance and neutral to alkaline pH values, on the western part of the island. Aquatic habitats in the larger valleys on the eastern side of Île de la Possession, with a low conductivity and slightly acid pH values, were characterized by the Trinema assemblage. Weighted averaging and calibration were used to develop a statistical transfer function to infer the pH of freshwater bodies from the testate amoebae assemblages. The model is usable over a pH range of 5 to 9.

Testate Amoeba (Rhizopoda) Diversity in Plankton of the Upper Paraná River floodplain, Brazil

In this study we examine the influence of environmental variability on the α and β diversity of testate amoeba assemblages from plankton samples. The samples were collected in the littoral and pelagic zones of the rivers and lagoons of the Parana River floodplain, over one hydrological cycle. Seventy-three species were identified. Alpha diversity was similar in both lagoons and rivers. Although the relationship between α diversity and water level was significant, it was not consistent for all environments, i.e. the pelagic and littoral zones of rivers and lagoons. Temporal β diversity was low and unrelated to environmental stability. Despite the high connectivity among floodplain environments and the suggested homogenizing effect of the flood pulse, spatial β diversity was high, mainly between rivers and lagoons. Also, testate amoeba species composition seems to be more predictable than local species richness.

Influence of Environmental Heterogeneity on the Structure of Testate Amoebae (Protozoa, Rhizopoda) Assemblages in the Plankton of the Upper Paraná River Floodplain, Brazil

AbstractIn freshwater environments, testate amoebae are usually found associated with macrophytes and sediments and many studies have suggested that their occurrence in plankton samples is accidental. This implies that predictable patterns detected in planktonic assemblages should not be observed in testate amoebae assemblages. This hypothesis was tested in this study. Plankton samples were collected from different environments in the Upper Paraná River floodplain. Results show that patterns in species composition and abundance of testate amoebae are predictable, and that dominant species tend to present characteristic shell morphology in hydrologically different environments. We suggest that testate amoebae must be routinely included in plankton ecology studies, at least in floodplain environments.