© Barbara Wojtasik, HydroBiolLab
Citation: Wojtasik B. 2016. Meiobenthos – different definitions and criteria applied [In:] B. Wojtasik, J. Sosiński, P. Pacyga. MeioEco.com application for ecological status analysis (http://portal.meioeco.com), 2016 r.

Meiobenthos – different definitions and criteria applied

Key words: meiobenthos, macrobenthos, size, definitions, errors, MeioEco

Benthic organisms, apart from taxa classification, are divided into three size-dependent groups: microbenthos, meiobenthos and macrobenthos. Each group contains organisms of different taxonomic units. In the case of microbenthos the lower size limit is unrestricted, similarly the upper size limit for macrobenthos is not specified. Both values, the upper and lower size limit, are essential for meiobenthos. Different definitions of meiobenthos do not specify exactly the sizes of studied specimens belonging to the group and consequently they can belong to two size classes (meio- and macrobenthos and meio- and microbenthos) simultaneously or not fall into any of them. The lack of an unambiguous definition specifying the size criterion for meiobenthos influences obtained results and possibility of comparison.

The ample literature concerning benthic organisms often provides size dependent group classification into microbenthos, meiobenthos and macrobenthos. Each group contains organisms belonging to different taxonomic units. In the case of microbenthos the lower size limit is unrestricted, similarly the upper size limit for macrobenthos is not specified. Both values, the upper and lower size limit, are essential for meiobenthos. There are different definitions of meiobenthos size (Table 1) and also various definitions of macrobenthos lower size limit, which is essential with regard to meiobenthos (Table 2). Therefore some organisms can be classified as belonging to two groups simultaneously or to none of the above mentioned groups. The concept that these are organisms passing through a sieve of given mesh size (different in particular definitions) leaves a wide margin of arbitrariness depending on animals' measurements (longitudinal and transverse), their flexibility, type of preservatives used for samples (Gaston et al. 1996) or alive animals sieved, presence of limbs or setae, type of bottom sediment they have been collected with, rapidity of water flux used for sample washing and mesh type. Inaccuracy of the definition applies even to the term of 'mesh size', as samples are washed with the use of frames with mesh stretched, where 1.0 mm means the length of a square side or the mesh diameter. Sieves with rhombus or polygonal mesh are also used. The information that the mesh is a 1.0 mm square (Żmudziński et al. 2002) in the definition of meiobenthos size is included only in few papers. There is a lack of detailed information concerning efficiency of the sieve washing process for particular taxa, and especially concerning loss during washing with respect to the bottom sediment type the sample has been collected with. Whereas, the methods of zoocenological analysis of isolated and identified organisms is presented meticulously. Since whole large functional groups, like macrobenthos and meiobenthos, are being more commonly used to assess water quality (Hawkes 1979, De Pauw & Vanhooren 1983, Särkkä 1992, Simboura & Zenetos 2002, Clarke et al. 2003, Czerniawska-Kusza 2005, Dye 2005, Chainho et al. 2007) it seems essential that the definition concerning conditions under which a given organism is classified as belonging to a particular size group should become more specific. Meiobenthos as a complex group of organisms is subject to further divisions, among others to marine and freshwater, permanent (specimens belonging to the given group throughout their life-cycle) and temporary (macrobenthos young stages). Although according to some authors (Geire 1993, 2009, Szymelfenig et al. 1995, Soltwedel 1997, Gal’tsova et al. 2004, Radziejewska et al. 2006, Brandt et al. 2007) Protista, particularly Foraminifera are regarded meiobenthos representatives while others restrict marine meiobenthos to Metazoa (Reise 1979, Sommerfield & Warwick 1996, Schizas & Shirley 1996). Despite advanced statistical analyses: Canoco (Braak & Similauer 1998), Primer (Clarke & Gorley 2006) used among others to estimate meiobenthos group, with the lack of regulated meiobenthos definition or standard procedure of isolating meiobenthos specimens from sediment, the obtained results are often incomparable and in many cases marred with error. The aim of the presented paper is the analysis of various criteria applied to meiobenthos and macrobenthos (the lower size limit) size and a proposal for standardisation of the definition and classification methodology while maximally preserving the so far applied criteria.

Material and methods
The analysis of the variety of meiobenthos definitions and size criteria used in practical procedures, macrobenthos lower size limit applied in research was based on the selected specialist literature. From available scientific literature only a one article sample was chosen for one size criterion. Results shown on Table 1 and Table 2, Fig.1 and Fig.2.

Results and discussion
The detailed data concerning the size of meiobenthos, the lower size limit of macrobenthos and the upper size limit of microbenthos, are presented in Table 1. The above specification shows undoubtedly that the size of organisms classified as meiobenthic can be treated very arbitrarily. Though the methodology states the lower size limit as 0.5 mm or 1.0 mm for macrobenthos (resulting from the sieve employed), the results frequently include only the groups which are obligatorily macrobenthal at the mature stage (Houston & Haedrich 1984, Bick & Arlt 2005), even though mature specimens of numerous species of Cladocera, Ostracoda and Copepoda exceed 0.5 mm and in many cases 1.0 mm (Sars 1903-1911, Bronstein 1947, Lang 1948, Rylov 1948, Loeblich & Tappan 1964, Dussart 1967, 1969, Delorme 1970, Flößner 1972, Sywula 1974, Athersuch et al. 1989, Huys et al. 1996, Rybak & Blędzki 2005, Murray 2006). Although the more of species of systematic groups such as Foraminifera, Nematoda, Cladocera, Ostracoda, Copepoda-Cyclopoida are enumerated as belonging to macrobenthos (size definition), they can be found only in few works concerning macrobenthos: Foraminifera (Wlodarska-Kowalczuk et al. 1998), Nematoda (Kröncke 1994), Ostracoda (Da Fonseˆca-Genevois et al. 2006). Another methological element is washing samples through a sieve (0.5 mm and 1.0 mm respectively) and regarding as meiobenthos all the organisms that passed through the sieve. As a result a large group of animals is not taken into account in the analyses – that is all those traditionally regarded as meiobenthos and which are larger than mesh size if 100 % efficiency of the washing process is assumed. In the case of a less efficient washing even larger a group is not subject to analyses. The method of sorting the organisms, which corresponds to the procedure used in granulometry (Pfannkuche & Thiel 1988, Soltwedel 1997), cannot be its equivalent due to a few major reasons: 1. meiobenthic organisms have different shapes, very often dissimilar from spherical which is ideal for washing, 2. the specific weight of meiobenthic organisms is usually significantly smaller than that of sediment grains which impedes the procedure, 3. the lack of compact or homogenous body built of many taxa and the presence of numerous limbs and setae affects the retention of washed specimens on mesh, on larger plant parts or on other organisms retained on the sieve, 4. a significant difference between body length and width causes the organisms' retention on the sieve (hydrodynamic – Stokes’ law, Reynolds number), 5. physical properties, i.e. liquid viscosity, surface tension and fraction counteract the free passing of specimens through a sieve. The washing process on a sieves was done in different parts in procedure of collected meio- or macrobenthos: before preservation (Kröncke 1994, Wlodarska-Kowalczuk et al. 1998, Bick & Arlt 2005, Feder et al. 2007) or after preservation (Guerrini et al. 1998, Kotwicki et al. 2004). This has an influence on the results (hydrodynamics rules as Stokes’ law, Reynolds number). The method of sorting the organisms on a sieve is not perfect. Theoretically the least loss was while washing Ostracoda, Foraminifera and juvenile Mollusca, what is undoubtedly due to their body shape and relatively high specific weight (Loeblich & Tappan 1964, Gal’tsova et al. 2004, Wiśniewska (Wojtasik) 2003). Different washing efficiency for particular meiobenthic taxonomic units is of a great importance for analysing biodiversity of communities and particularly for determining the occurrence density and relative number of particular taxa, as well as for other calculations like biomass. The standardisation of methods and criterion could constitute a new direction in ecohydrological monitoring and evolution of reservoirs, rivers, and seas using a group of meiobenthos as a bioindex, in particular of MeioEco method (Fig. 4) (Wojtasik 2009, Wojtasik 2013 a, b)

The conducted analyses show that the classification criterion according to the size of organisms is commonly applied to meiobenthos, whereas the size-taxonomic criterion is more often used for macrobenthos and that seems right due to many reasons. Still, in such a case, the same criterion should be applied to meiobenthos. Therefore, it seems necessary to abandon the procedure of 1.00 mm sieve washing and classify as meiobenthos all organisms considered permanent meiobenthos regardless of their size. As far as temporary meiobenthos is concerned if the organisms could theoretically pass through a 1.00 mm sieve, they should be classified as meiobenthos. The size criteria smaller than 1.00 mm for meiobenthos seem to be proper for sorting particular size groups of meiobenthos but not as the upper size limit for the entire group. A propose of standardisation of the definition and isolating procedures shown on Fig.3. The standardisation of methods and criterion could constitute a new direction in ecohydrological monitoring and evolution of reservoirs, rivers and seas using a group of meiobenthos as a bioindex, in particular of MeioEco method (Wojtasik 2013 a, b).


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Table 1. Meiobenthos – a size criterion,


Min size [mm]

Max size [mm]


Retained on a sieve 0.1

Bick & Ardt (2005)



Brandt et al. (2007)



Coull (1970)



Encyclopedia Britannica (2008)



Gal’tsova et al. 2004



Da Fonseˆca-Genevois et al. (2006)

Retained on a sieve 0.042 (0.063) or to deep-sea samples 0.031

Pass through a sieve 0.5 (1.0)

Giere (1993)

Retained on a sieve 0.052

Pass through a sieve 1.0

Guerrini et al. (1998)




Greater dimension than or equal to 0.1 mm

shortest dimension is less than 0.5 mm


Retained on a sieve 0.038

Pass through a sieve 1.0

Kotwicki et al. (2004)

0.3 (body length),

in procedure a sieve 0.08

Up to 4.0 (body length)

Kurashov (2002)

Retained on a sieve 0.042

Pass through a sieve 1.0

Pfannkuche & Thiel (1988)



Plinski (2007)

Equipment to collected samples with mesh gauze 0.04

Pass through a sieve 0.5

Reise (1979)

Retained on a sieve 0.063 or 0.045

Pass through a sieve 0.5

Schizas & Shirley (1996)

Pass through a sieve 0.53

Silva & Williams (2005)

Retained on a sieve 0.063

Pass through a sieve 0.5

Sommerfield & Warwick (1996)

Pass through the sieve 1.0

Szymelfenig et al. (1995)

Retained on a sieve 0.032

Pass through a sieve 0.25

Ye et al. (2005)

Retained on a sieve +/- 0.04

pass through sieve about +/- 1.0

Żmudziński (1997)

+/- 0.04

Smaller than 2.0, pass through a sieve about 1.0

Żmudziński et al. (2002)

Table 2. Macrobenthos – a size criterion of inferior border


Min size [mm]


Samples washed through a aperture sieve 0.6 (sometimes with aid of a mechanical-hydraulic elutriator), analyzed remaining animals. For some animals used a sieve 0.153

Barton & Anholt (1997)

Retained on a sieve 0.5

Bick & Ardt (2005)

Retained on a sieve 1.0

Feder et al. (2007)

> 0.5

Hawke (1979)

Retained on a sieve 0.52

Houston & Haedrich (1984)

Retained on a sieve 0.5 (juveniles - retained on a sieve 0.25)

Reise (1979)

Retained on a sieve 0.5 or 1.0

Wlodarska-Kowalczuk et al. (1998)

Retained on a sieve 0.4-1.0

Żmudziński (1997)

Fig.1. Different definitions and practical criterion for meio- and macrobenthos analysis (describe in text)

Fig.1. Different definitions and practical criterion for meio- and macrobenthos analysis (describe in text)

Fig.2. A result of used common procedures for collected meio- and macrobenthos

Fig.2. A result of used common procedures for collected meio- and macrobenthos

Fig.3. A propose of standardization of the definition and collected procedures for meio- and macrobenthos

Fig.3. A propose of standardization of the definition and collected procedures for meio- and macrobenthos

Fig. 4. The criterion used in MeioEco analysis

Fig. 4. The criterion used in MeioEco analysis

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