Meiobenthos

Meiobenthos, also called meiofauna, are small benthic invertebrates that live in both marine and fresh water environments. The term meiofauna loosely defines a group of organisms by their size, larger than microfauna but smaller than macrofauna, rather than a taxonomic grouping. In practice, that is organisms that can pass through a 1 mm mesh but will be retained by a 45 μm mesh, but the exact dimensions will vary from researcher to researcher. Whether an organism will pass through a 1 mm mesh will also depend upon whether it is alive or dead at the time of sorting.

The term meiobenthos was first coined in 1942 by Mare, but organisms that would fit into the meiofauna category have been studied since the 18th century. A comprehensive text on meiofauna is Introduction to the study of meiofauna by Higgins and Thiel (1988).

Meiofauna are most commonly encountered in sedimentary environments in both marine and fresh water environments, from the littoral to the deep-sea. They can also be found on hard substrates living on algae, the phytal environment, and sessile invertebrates (barnacles, mussel beds, etc.).

Sampling the meiobenthos is clearly dependent upon the environment and whether quantitative or qualititative samples are required. In the sedimentary environment the methodology used also depends on the physical morphology of the sediment. For qualititative sampling within the littoral zone, for both coarse and fine sediment, a bucket and spade will work. In the sub-littoral and deep water some form of grab (like the Van Veen Grab Sampler) is required, although a fine mesh (about 0.25 mm or less) would work also.

For the quantitative sampling of sedimentary environments at all depths a wide variety of samplers have been devised. The simplest is a plastic syringe with the end cut off to form a piston corer which can be deployed in the littoral zone, or in the sub-littoral using SCUBA gear. Generally the deeper the water the more complicated the sampling process becomes. For sampling the meiofauna on hard substrates, phytal and epizooic environments, the only practical methodology is to cut or scrape off a known area of substrate and place it in a plastic bag.

There are a wide variety of methods for extracting meiofauna from the samples of their habitat depending upon whether live or fixed specimens are required. For extracting live meiofauna one has to contend with the large number of species that cling or attach themselves to the substrate when disturbed. In order to get the meiofauna to release their grip there are three methodologies available.

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Wikipedia