Patchiness and life cycle of intertidal foraminifera: Implication for environmental and paleoenvironmental interpretation

This study was carried out at the mouth of a small river of the Atlantic coast of France, with the aim of investigating medium-scale patchiness and life cycles in time series samples of foraminiferal assemblages. ng was carried out at three stations, irregularly between January 2000 and September 2001, and on a monthly/bimonthly basis, between September 2001 and September 2003. A monthly sampling was continued until April 2004 at two stations. Samples were also collected at ten selected sampling sites, in October 2002, with the aim of getting information about spatial distribution of foraminifera, either at the same intertidal level or at different elevations. Living assemblages were studied in each sample, and compared to total assemblages from about half of the samples. A pseudoreplication procedure was used to circumvent small-scale patchiness. tudy confirms that paralic foraminifera do not have reproducible annual life cycles and that isolated samplings of living assemblages may provide different or even contradictory results, depending if the sampling is done during the bloom or not. It also shows that, even if blooms occur at periods close together for all the species at neighboring stations, differences exist between stations located in the same environment, 10 m apart. Thus, isolated or even seasonal samplings of living foraminiferal assemblages cannot be considered as giving a valuable image of environmental conditions. Conversely, total assemblages provide integrated information about homogenized assemblages over a given period of time. This study demonstrates that exchanges of tests by transport between low marsh to high marsh is weak or absent, but small-scale post mortem transport leads to the homogenization of the assemblage.