Meiofauna in sediments

Meiofauna is collected from the sediment cores, obtained from a perplex tubes of 3,6 cm diameter (surface ~10 cm-2 is appropriate for all types of sediment), inserted 15 cm deep into the seabed. From one site six (at least three) replicates are taken. Sediment is gently pushed out from the tube and cut into the slices. Te slices are usually taken from particular layers: 0-1, 1-2, 2-3, 3-4, 4-5, 5-10 and 10-15 cm. Sometimes core is cut every 1 cm into even slices. Each sediment slice (subsample) is placed into the separate jar, fixed with 4 % neutral formaldehyde solution and stained with Bengal Rose, to obtain a pink/reddish color of the sample. For extraction of meiofauna from sediment are used two methods depending of the amounts of the detritus or silt-clay in the sediment. Decantation method - when the sediment is a sand with low amounts of detritus or silt-clay. In the laboratory, each slice is placed in the 1000 ml cylinder, filled with tap water and shaken vigorously, to suspend the sediment grains. The water is then filtered through 0.038 mm screen, and the procedure of shaking and flotation is repeated 10 times. All meiofauna organisms are retained on the screen, are gently washed into the Petri dish with measuring grid on the bottom and counted under the low power stereo microscope. Density gradient centrifugation method - the extraction from mud or detritus is most efficiently using a density gradient in a centrifugation procedure (Heip et al. 1985). In this method liquid with a density larger than the density of meiofaunal organisms can be used (Ludox, density of 1.15) The method consist: placement of sediment sample into the Ludox solution, centrifuge it with 1800 g for 10 min. The meiofauna organisms are retained in the 'gel', once the sediment is on the end of the tube. Repeat centrifugation three times more. This method does not work for heavy foraminifera, since their density is often equal to the sediment grain. In the lab, the meiofauna organisms are counted on the measuring grid, usually 1000 specimens per sample (sediment slice).
Basic handboks:
Heip C., Vincx M., Vranken G., 1985, The ecology of marine nematodes. Oceanographic Marine Biology Annual Review 23: 399-489.
Vincx M., 1996, Meiofauna in marine and freshwater sediments. [In:] Methods for the examination of organisms diversity in soils and sediments (ed G.S. Hall). CAB INTERNATIONAL