|Basic Information||Biotope classification||Ecology||Habitat preferences and distribution||Species composition||Sensitivity||Importance|
SS.SMu.OMu.ForThy recorded () and expected () distribution in Britain and Ireland (see below)
The presence of the characterizing and other species in this biotope is primarily determined by the occurrence of a suitable substratum rather than by interspecific interactions. However, the component species modify the habitat and, in that way, affect each other. The following points may be relevant to this biotope. Deposit feeders sort and process sediment particles and may result in destabilization of the sediment, which inhibits survival of suspension feeders. This can result in a change in the vertical distribution of particles in the sediment that may facilitate vertical stratification of some species with particle size preferences. Vertical stratification of species according to sediment particle size has been observed in some soft-sediment habitats (Petersen, 1977). Polychaetes also significantly influence nutrient fluxes of nitrogen and phosphorus at the sediment-water interface, owing to their burrowing activity promoting oxygenation of the substrata. The burrowing and feeding activities of the macrofauna are likely to modify the fabric and increase the mean particle size of the upper layers of the substrata by aggregation of fine particles into faecal pellets. Such actions create a more open sediment fabric with a higher water content which affects the rigidity of the seabed (Rowden et al., 1998). Such alteration of the substratum surface can affect rates of particle resuspension.
Bioturbation is particularly important in controlling chemical, physical and biological processes in marine sediments, especially when the influences of physical disturbances such as wave action or strong currents are minimized (Widdicombe & Austen, 1999).
Another factor determining the distribution of assemblages is the annual variation of temperature in bottom layers, influenced by the amount of stratification in the water column. COS.ForThy occurs in water depth greater than 100 m in the North Sea and Celtic Sea, i.e. deeper than the seasonally stratified water. Differences in stratification north and south of the Dogger Bank might explain why cold water species do not go further south than the Dogger Bank (Kunitzer et al., 1992).
In Loch Nevis there is greater vertical mixing and primary production, therefore a higher rate of deposition of organic material would be present and able to support greater populations of benthic animals (McIntyre, 1961).
Most of the species living in deep mud biotopes are generally cryptic so are protected to some extent from visual surface predators. However, some species of foraminifera, such as Astrorhiza sp. usually live on the substratum surface. The arm tips of Amphiura chiajei, which is often present in this biotope, are also an important food source for demersal species.
Foraminifera are able to move along the sediment surface. Feeding takes place when the animal is stationary, by developing a network of numerous thin extensions of cytoplasm called ‘reticulopodia’ or ‘pseudopodia’ (Buchanan & Hedley, 1960; Wetmore,1995). Buchanan & Hedley (1960) noted that the pseudopodia of Astrorhiza lamicola ramify over the sediment surface and through the interstitial spaces to a depth of 2-3mm, extending to a distance of ~7cm from the animal.
Depending on size and available food, foraminifera, prey on dissolved organic molecules; bacteria, diatoms and other single-celled phytoplankton; small crustacea and recently metamorphosed Echinocardium flavesens (Buchanan & Hedley, 1960; Wetmore, 1995; Rivkin & DeLaca, 1990).
Buzas (1978) suggested that foraminiferans probably also represent an important food source for benthic macrofauna. Predation was thought mainly to be by demersal fish species (McIntyre, 1961).
Dando & Southward (1986), Southward (1986), and Spiro et al. (1986) found that different species of Thyasira species show a range of nutritional dependence on bacteria in their gills; from none (heterotrophs) to complete dependence (chemoautotrophs).
No information is known about the reproduction and recruitment of foraminifera within this biotope.
Larval development of Thyasira equalis is lecithotrophic and the pelagic stage is very short or quite suppressed. This agrees with the reproduction of other Thyasira sp., and in some cases (Thyasira gouldi) no pelagic stage occurs at all (Thorson, 1946). This means that larval dispersal is limited. No information relating to fecundity of Thyasira species within the biotope was found, however information is available for another Thyasira sp., and it is possible that fecundity is similar in species within the COS.ForThy biotope. Spawning of Thyasira gouldi occurs throughout the year, with up to 750 eggs produced each time. No information is available on the mechanism of spawning or the number of spawnings per year.
Other species that usually occur in the biotope, such as polychaetes and brittlestars usually have planktonic development, an annual reproductive cycle and are fecund.
This review can be cited as follows:
Riley, K. 2002. Foraminiferans and Thyasira sp. in deep circalittoral soft mud. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 03/09/2015]. Available from: <http://www.marlin.ac.uk/habitatecology.php?habitatid=215&code=2004>