The Biotope: Factors and Study Methods

When describing the habitats of meiofauna, grain size is a key factor since it directly determines spatial and structural conditions and indirectly determines the physical and chemical milieu of the sediment. Poorly sorted sediment particles (e.g., sand mixed with gravel and silt) become tightly packed and the interstitial pore volume is often reduced to only 20% of the total volume. Well-sorted (coarse) sediments contain up to 45% pore volume. According to Ruttner-Kolisko (1962), most field samples of unsorted freshwater sand have 40% pore volume.

Aside from pore volume, the external surface area of the sediment particles is an important determinant of meiobenthic life. It directly defines the area available for the establishment of biofilms (mucus secretions of bacteria, fungi, diatoms, fauna), which, under natural conditions, form the matrix into which the sediment particles are embedded. Thus, particle surface is an important parameter for microscopic animal life. This internal surface is unbelievably large: for a 1-m3 stream gravel it has been calculated to amount to about 400 m². One gram of dry fine sand with a median particle diameter of 63–300µm may have a total surface area of 8–12.5 m²; if it consists mostly of diatom shells, this value can even exceed 20 m², whereas for 1 g of coarse-grained calcareous sand a value of just 1.8 m² was calculated (Suess 1973; Mayer and Rossi 1982).