Thecamoeba in succession series of some peat-bog vegetations

Abstract

The Thecamoeba belong to the protozoan class Rhizopoda. The thecae, or shells, are built up of rather resistant material, usually pseudochitin or silica. This characteristic faciliates identification in preserved and even dried or subfossil material. They occur in very wet (submerged) to moist habitats. In the succession series of the vegetation in pools and ditches we can find different conditions, and many factors will change in the surrounding water during the succession, e. g. relative humidity, influence of rainwater on trophic level and pH value. Particularly the oligotrophic peat-moor vegetations in Germany have been a subject of study of thecamoebian ecology (HARNISCH, 1927; JUNG, 1936). HARNISCH was the first to describe several associations of Thecamoeba, that showed a distinct preference for specified vegetation types. The mesotrophic and eutrophic wet surroundings have scarcely been investigated (DE GRAAFF, (1956). There is still much to be learned about the ecology of Thecamoeba in the vegetation of the peat-bogs in the lower part of the Netherlands. As an example one succession series of the vegetation in such a peat-bog shall be discussed. The succession starts in open water about 1,5 to 3 metres deep. The first plants found belong to the Potametalia (WESTHOF and DEN HELDT, 1969). In this association organic material accumulates on the bottom. In this way the bottom is built up. When this mud is at about 50 centimetres below surface the plants belonging to the Scirpo-Phragmitetum (WESTHOF and DEN HELDT, 1969) can be found. These plants form a strong mat of roots that “floats” on the underlying mud and dead plant material. This mat ultimately reaches the surface of the water thus making the settlement of other plants possible. These plants belong to the association Thelypterido-Phragmitetum (WESTHOF and DEN HELDT, 1969). Further accumulation of organic matter and the growth ofSphagnum leads to the last association in which samples were taken: The Pallavicinio-Sphagnetum (WESTHOF and DEN HELDT, 1969). Two territories were visited, both Dutch nature reserves in the northwestern part of the province of Overijsel: “e Weerribben” and “de Lindevallei”. In the Weerribben two types of plant succession series were sampled, one beginning in open eutrophic water and the other in more isolated parts beginning in mesotrophic water. The first we callPhragmites australis series and is discussed above, the secondCarex series (named after the dominating plant species or genus). In the Lindevallei one series was sampled, resembling thePhragmites australis series of the Weerribben which also shall be calledPhragmites australis series. Samples were taken by pressing liquid out of mosses. These mosses were arranged in a microzonation along with the zonation of higher plants, going from submerged to moist vegetation. At The similarity between the drier stages of our peat-bogs and those of Jung's peat-moors, can be explained as due to the increasing influence of rainwater in the bogs. Peat-moors are almost entirely drained of rainwater. There is a strong similarity in all series, in relation to humidity. Differences between the series may be found after more detailed analysis of data, because this survey refers only to dominant and codominant species.