Biogeographic Distribution of Modern Thecamoebians in a Transect Along the Eastern North American Coast
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Thecamoebians in general, and the superfamily Arcellacea in particular, seem ideally suited as paleolimnological tools. The scarcity of baseline biogeographical studies, however, severely limits their value as modern analogs for paleoecological reconstructions. A comparison of the modern arcellacean fauna studied from four lakes from Baffin Island (63°N), Nova Scotia (45°N), Virginia (38°N) and southern Florida (27°N) with the information available in the literature shows how several trends in arcellacean distribution exist in eastern North America.
Several species (Centropyxis aculeata, Centropyxis constricta, Difflugia oblonga, and Pontigulasia compressa) are ubiquitous, while others seem to have more restricted distribution. Climatic and limnological conditions appear to be the factors which determine the distribution of the less ubiquitous taxa. Arcella vulgaris, Difflugia globulus, Difflugia urceolata (especially forma elongata), Difflugia mens, Heleopera sphagni, and Nebella collaris are most abundant in northern sites, while Cucurbitella tricuspis, Difflugia bacilli fera, Difflugia corona, Difflugia fragosa, Lagenodifflugia vas, and Lesquereusia spiralis tend to be more abundant in southern areas. The species C. aculeata, C. constricta, D. urceolata, and possibly D. urens appear to tolerate oligotrophic conditions, while C. tricuspis appears to prefer eutrophic conditions.
KeywordsNova Scotia United States Geological Survey Eutrophic Condition Diatom Frustule Oligotrophic Condition
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