Meiobenthos
Encyclopedia
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 good comprehensive text on meiofauna is Introduction to the study of meiofauna by Higgins and Thiel (1988).
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.).
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.
The first, and simplest, is osmotic shock, this is achieved by submerging the sample in fresh water (clearly this will only work for marine samples) for a few seconds. This will cause the organisms to release after which they can then be shaken free from the substrate and filtered out through a 45 μm mesh and immediately returned to fresh filtered seawater. Many organisms will come through this process unharmed as long as the osmotic shock does not last too long.
The second methodology is the use of an anaesthetic. The preferred solution for meiobenthologists is isotonic magnesium chloride (7.5g MgCl2 · 6H2O in 100 ml of distilled water). The sample is immersed in the isotonic solution and left for a period of 15 min, after which the meiofauna are shaken free of the substrate and again filtered out through a 45 μm mesh and immediately returned to fresh filtered seawater.
The third methodology is Uhlig's seawater ice technique. This relies on the organisms moving ahead of a front of ice cold seawater moving down through the sample ultimately forcing them out of the sediment. It is most effective on samples from temperate and tropical regions.
For major studies where large numbers of samples are collected concurrently, samples are normally fixed using 10% formalin solution and the meiofauna extracted at a later date. There are two main extraction methodologies. The first, decantation, works best with coarse sediments. Samples are shaken in an excess of water, the sediment is briefly allowed to settle and the meiofauna filtered off. The second methodology, the floatation technique, works best with finer sediments were the mass of the sediment particles is close to that of the meiofauna. The best solution to use is the colloidal silica, Ludox. The sample is stirred into the Ludox solution and left to settle for 40 min, after which the meiofauna are filtered out. With both methodologies repeated extractions should be made (at least three) with each sample to ensure that at least 95% of the fauna is extracted.
appear in bold text.
Benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
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
Microfauna
Microfauna refers to microscopic organisms that exhibit animal-like qualities. Microfauna are represented in the animal kingdom and the protist kingdom...
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 good comprehensive text on meiofauna is Introduction to the study of meiofauna by Higgins and Thiel (1988).
Collecting the meiobenthos
Meiofauna are most commonly encountered in sedimentary environments in both marine and fresh water environments, from the littoralLittoral
The littoral zone is that part of a sea, lake or river that is close to the shore. In coastal environments the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It always includes this intertidal zone and is often used to...
to the deep-sea. They can also be found on hard substrates living on algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, the phytal environment, and sessile invertebrates (barnacles, mussel beds, etc.).
Sampling methodologies
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) 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.
Extraction methodologies
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.The first, and simplest, is osmotic shock, this is achieved by submerging the sample in fresh water (clearly this will only work for marine samples) for a few seconds. This will cause the organisms to release after which they can then be shaken free from the substrate and filtered out through a 45 μm mesh and immediately returned to fresh filtered seawater. Many organisms will come through this process unharmed as long as the osmotic shock does not last too long.
The second methodology is the use of an anaesthetic. The preferred solution for meiobenthologists is isotonic magnesium chloride (7.5g MgCl2 · 6H2O in 100 ml of distilled water). The sample is immersed in the isotonic solution and left for a period of 15 min, after which the meiofauna are shaken free of the substrate and again filtered out through a 45 μm mesh and immediately returned to fresh filtered seawater.
The third methodology is Uhlig's seawater ice technique. This relies on the organisms moving ahead of a front of ice cold seawater moving down through the sample ultimately forcing them out of the sediment. It is most effective on samples from temperate and tropical regions.
For major studies where large numbers of samples are collected concurrently, samples are normally fixed using 10% formalin solution and the meiofauna extracted at a later date. There are two main extraction methodologies. The first, decantation, works best with coarse sediments. Samples are shaken in an excess of water, the sediment is briefly allowed to settle and the meiofauna filtered off. The second methodology, the floatation technique, works best with finer sediments were the mass of the sediment particles is close to that of the meiofauna. The best solution to use is the colloidal silica, Ludox. The sample is stirred into the Ludox solution and left to settle for 40 min, after which the meiofauna are filtered out. With both methodologies repeated extractions should be made (at least three) with each sample to ensure that at least 95% of the fauna is extracted.
Meiofaunal taxa
Based on the scheme of Nielsen (2001). Meiofaunal taxaappear in bold text.
- Protozoa
- ForaminiferaForaminiferaThe Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...
- Ciliophora
- Foraminifera
- Animalia—Eumetazoa
- CnidariaCnidariaCnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
- Triploblastica—Bilateria
- Protostomia—Spiralia
- Schizocelia
- SipunculaSipunculaThe Sipuncula or Sipunculida is a group containing 144-320 species of bilaterally symmetrical, unsegmented marine worms...
- Articulata
- MolluscaMolluscaThe Mollusca , common name molluscs or mollusksSpelled mollusks in the USA, see reasons given in Rosenberg's ; for the spelling mollusc see the reasons given by , is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest...
- Euarticulata
- Annelida
- Oligochaeta
- PolychaetaPolychaeteThe Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
- Panarthropoda
- Onychophora
- Arthropoda
- Tardigrada
- AmphipodaAmphipodaAmphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. The name amphipoda means "different-footed", and refers to the different forms of appendages, unlike isopods, where all the legs are alike. Of the 7,000 species, 5,500 are classified...
- CladoceraCladoceraCladocera is an order of small crustaceans commonly called water fleas. Around 620 species have been recognised so far, with many more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are long, with a down-turned head, and a carapace covering the apparently...
- CumaceaCumaceaCumacea is an order of small marine crustaceans, occasionally called hooded shrimp. Their unique appearance and uniform body plan makes them easy to distinguish from other crustaceans.-Anatomy:...
- HarpacticoidaCopepodCopepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
- IsopodaIsopodaIsopods are an order of peracarid crustaceans, including familiar animals such as woodlice and pill bugs. The name Isopoda derives from the Greek roots and...
- Ostracoda
- MystacocaridaMystacocaridaMystacocarida is a subclass of crustaceans, that form part of the meiobenthos. They are less than long, and live interstitially in the intertidal zones of sandy beaches.-Taxonomy:...
- SyncaridaSyncaridaSyncarida is a superorder of crustaceans, comprising the two orders Anaspidacea and Bathynellacea. Fifty-nine genera are known, in six families:Anaspidacea Calman, 1904*Anaspididae Thomson, 1893*Koonungidae Sayce, 1908*Psammaspididae Schminke, 1974...
- TanaidaceaTanaidaceaThe crustacean order Tanaidacea make up a minor group within the class Malacostraca. There are about 940 species in this order.-Description:...
- ThermosbaenaceaThermosbaenaceaThermosbaenacea is a group of crustaceans that live in thermal springs in fresh water, brackish water and anchialine habitats. They have occasionally been treated as a distinct superorder , but are generally considered to belong to the Peracarida...
- Halacarida
- Pycnogonida
- Palpigradida
- Insecta
- Annelida
- Euarticulata
- Mollusca
- Bryozoa
- EntoproctaEntoproctaEntoprocta, whose name means "anus inside", is a phylum of mostly sessile aquatic animals, ranging from long. Mature individuals are goblet-shaped, on relatively long stalks. They have a "crown" of solid tentacles whose cilia generate water currents that draw food particles towards the mouth, and...
- Ectoprocta
- Entoprocta
- Paranchymia
- Platyhelminthes (TurbellariaTurbellariaThe Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes , and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from to in length...
) - NemerteaNemerteaNemertea is a phylum of invertebrate animals also known as "ribbon worms" or "proboscis worms". Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela. Although most are less than long, one specimen has been estimated at , which would make it the longest animal ever...
- Platyhelminthes (Turbellaria
- Gnathifera
- Rotifera
- Gnathostomulida
- Chaetognatha
- Cycloneuralia
- Gastrotricha
- Introverta
- Nematoda
- Nematophora
- Cephalorhyncha
- PriapulidaPriapulidaPriapulida is a phylum of marine worms. They are named for their extensible spiny proboscis, which, in some species, may have a shape like that of a human penis...
- KinorhynchaKinorhynchaKinorhyncha is a phylum of small marine pseudocoelomate invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos...
- LoriciferaLoriciferaLoricifera is a phylum of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca....
- Priapulida
- Sipuncula
- Deuterostomia
- Phoronida
- Brachiopoda
- Neorenalia
- Pterobranchia
- Echinodermata
- Cyrtotreta
- Entropneusta
- Chordata
- Urochordata
- Notochordata
- Schizocelia
- Protostomia—Spiralia
- Cnidaria