Abstract

The temporal variability (over 27 months) in abundance, depth of life in the sediment, and species diversity of hard-shelled, live (stained) foraminifera in an intertidal area has been determined. Throughout the investigation period, the same three species (Haynesina germanica, Ammonia beccarii (tepida), Elphidium excavatum) were dominant at the two investigated stations, the maximum abundance of all species (dominant and subsidiary) was in the surface 0.25 cm, and there was a general lack of seasonal change in the vertical distribution of the foraminifera. Seasonality does not seem to be a controlling factor for the vertical distribution of individuals in this area and none of the foraminifera showed high subsurface abundances. Because of the difference in depth position of the redox boundary within the sediment (often 1 cm) and the maximum abundance of individuals (surface 0.25 cm) the former cannot be the main factor limiting their vertical distribution of abundance. The generally high dominance of individuals in the surface few millimeters is probably related to the presence there of microalgal food and limited burrowing activity of the sparse macrofauna. Subsidiary species colonized the area ephemerally, thus the number of species recorded varied from one season to another. The minimum and maximum number of species found at any single sampling event were 5 and 22, whereas the cumulative number of stained species found throughout the investigation period was 35 (plus at least three soft-shelled forms). Species diversity is one of the principal univariate methods used to assess both natural variability and possible human impacts. The large natural seasonal variability demonstrated here suggests that caution should be taken in assessing the significance of diversity changes when based on occasional sampling only.

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