「Testate amoeba communities in lakes: Recent ecology and paleoenvironmental/paleoclimatic applications」

Dr. WALL Adeline A.J.(JSPS Postdoctorate Researcher)

Testate amoebae are unicellular organisms (Protozoa) enclosed in a solid shell, or test. These organisms considered as worldwide distributed, are commonly found in a wide range of moist and freshwater environments and habitats, i.e. pounds, peatlands, lakes, soils. In terrestrial and aquatic ecosystems testate amoebae are studied for their bioindicator potential, mostly in peatlands. In lakes, they are still poorly described even if some studies characterized lacustrine testate amoebae as good environmental tools for environment quality (Escobar et al., 2008; Lorencová, 2009; Roe et al., 2010). However, testate amoeba determination is mostly based on their shell morphology, and the good preservation of these shells in anoxic conditions like lake sediments and peat, provide the opportunity to proceed to paleoenvironmental studies (McCarthy et al., 1995; Burbidge and Schröder-Adams, 1998; Dallimore et al., 2000; Booth et al., 2002; Patterson et al., 2002; Boudreau et al., 2005; Reinhardt et al., 2005).

My research is focused on testate amoeba communities living at the water-sediment interface in lakes. In response at the global warning preoccupation, the development of new indicators of environmental and climatic changes is essential to increase our understanding of the processes. Consequently for this purpose, the analysis of ecological meaning of present day’s analogues is needed. The main objective of my research is then to improve the knowledge on testate amoeba communities in lakes in order to better understand the response of past assemblages to climatic oscillations.

My thesis was performed on testate amoeba communities in several French lakes and divided in two parts. The first part concerned a comparative study of testate amoeba communities at different depth water-sediment interface (2 m, 5 m, 10 m, 15 m, 30 m, 90 m depending on maximum depths) of 3 lakes with different trophic levels (Lake Pavin: oligo-mesotrophic; Lake Clairvaux: mesotrophic; Lake Bonlieu: eutrophic). The second part focused on a paleoenvironmental analysis of testate amoeba assemblages in a well-known sediment sequence from Lake Lautrey (Magny et al., 2006) dating from the transition between the Late glacial and the early Holocene climatic periods (15.7-11 ky cal BP) (Wall et al., 2010 a). In parallel, methodological approaches were discussed in terms of filtration and extraction of testate amoebae (Wall et al., 2010 b).

The major results of these studies confirm the indirect or direct effects of some environmental factors on testate amoeba communities, i.e. nutritive resources (quantity and diversity), dissolved oxygen concentration, temperature (thermocline position), trophic status and climatic oscillations. Testate amoeba communities show a zonation with the depth, controlled by physical-chemical parameters. The interest of these organisms as bioindicators for recent and past environmental and climatic conditions is clearly highlighted by the conclusions of these studies. The paleoenvironmental testate amoeba assemblage study represents one of the rare ones realized in lakes (first one in France) and the more complete one for those climatic periods.

My JSPS postdoctoral research project at the CER is the continuation of my previous research in France. This project aims to give more information on testate amoeba communities at the water-sediment interface of Lake Biwa following different depths. In addition, the study will be done as an annual survey, month by month of the communities, in order to have an estimation of the seasonality of the species composition and abundance patterns. This study will be the first ecological study of testate amoebae in lakes in Japan.

My seminar communication will focus mostly on my previous works and will explain the objectives of my research at CER.

Refecences

- Booth RK, Jackson ST, Thompson TA (2002) Paleoecology of a northern Michigan lake and the relationship among climate, vegetation, and Great Lakes water-levels. Quaternary Research 57: 120-130

- Boudreau REA, Galloway JM, Patterson RT, Kumar A, Michel FA (2005) A palaeolimnological record of Holocene climate and environmental change in the Temagami region, northeastern Ontario. Journal of Paleolimnology 33: 445-461

- Burbidge SM, Shröder-Adams CJ (1998) Thecamoebians in Lake Winnipeg: a tool for Holocene Paleolimnology. Journal of Paleolimnology 19: 309-328

- Dallimore A, Schröder-Adams CJ, Dallimore SR (2000) Holocene environmental history of thermokarst lakes on Richards Island, Northwest Territories, Canada: thecamoebians as paleolimnological indicators. Journal of Paleolimnology 23: 261-283

- Escobar J, Brenner M, Whitmore TJ, Kenney WF, Curtis JH (2008) Ecology of testate amoebae (thecamoebians) in subtropical Florida lakes. Journal of Paleolimnology 40: 715-731

- Lorencovà M (2009) Thecamoebians from recent lake sediments from the Šumava Mts, Czech Republic. Bulletin of Geosciences 84(2), 359-376

- Magny M, Aalbersberg G, Bégeot C, Benoit-Ruffaldi P, Bossuet G, Disnar JR, Heiri O, Laggoun-Defarge F, Mazier F, Millet L, Peyron O, Vannière B, Walter-Simonnet AV (2006) Environmental and climatic changes in the Jura mountains (eastern France) during the Lateglacial-Holocene transition: a multi-proxy record from Lake Lautrey. Quaternary Science Reviews 25: 414-445

- McCarthy FMG, Collins ES, McAndrews JH, Kerr HA, Scott DB, Medioli FS (1995) A comparison of postglacial Arcellacean (Thecamoebian) and pollen succession in Atlantic Canada, illustrating the potential of Arcellaceans for palaeoclimatic reconstruction. Journal of Paleontology 69: 980-993

- Patterson RT, Dalby A, Kumar A, Henderson LA, Boudreau REA (2002) Arcellaceans (thecamoebians) as indicators of land-use change: settlement history of the Swan Lake area, Ontario as a case study. Journal of Paleolimnology 28: 297-316

- Reinhardt EG, Little M, Donato S, Findlay D, Krueger A, Clark C, Boyce J (2005) Arcellacean (thecamoebian) evidence of land-use change and eutrophication in Frenchman’s Bay, Pickering, Ontario. Environmental Geology 47: 729-739

- Roe HM, Patterson RT, Swindles GT (2010) Controls on the contemporary distribution of lake thecamoebians (testate amoebae) in the Greater Toronto Area and their potential as water quality indicators. Journal of Paleolimnology 43:955-975

- Wall AAJ, Gilbert D, Magny M, Mitchell EAD (2010a) Testate amoeba analysis of lake sediments: impact of filter size and total count on estimates of density, diversity and assemblage structure. Journal of Paleolimnology 43: 689-704

- Wall AAJ, Magny M, Mitchell EAD, Vannière B, Gilbert D (2010b) Response of testate amoeba assemblages to environmental and climatic changes during the Lateglacial–Holocene transition at Lake Lautrey (Jura Mountains, eastern France). Journal of Quaternary Science 25: 945-956