Sensitivity characteristics of the habitat and relevant characteristic species
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This biotope is characterized its presence exclusively within lagoon habitats. There are only 358 examples of these rare and unusual habitats in the UK (Bamber et al., 2001), which make up a total of 5,184 hectares of coastline habitat (UKNEA, 2011). There are a number of factors which are thought to contribute to the rarity of these habitats in the UK. It is thought that many sedimentary lagoons do not appear in many of the areas suitable for them because of the macro-tidal regimes found within the north east Atlantic (Barnes, 1991). The high energy coastlines common around the UK mean that shingle lagoons can be both created from off shore glacial deposits and removed, therefore they are often short lived on geological time scales, and are now less common than they were at the end of the last ice age (Bamber et al., 2001). The low energy nature of lagoons also means that they can be susceptible to silting up which can elevate their basins above the level for percolation input. Combined with perimeter shingle ridges being elevated by storms, reducing water input via overtopping, can cause lagoons to become freshwater lakes (Bamber et al., 2001). The somewhat ephemeral nature of lagoons, and their susceptibility to change, means that the succession of habitats and consequently the biotopes found within them can be quicker and more noticeable than those found within other more stable physical environments.
The salinity regime within this biotope makes it suitable for Fucus ceranoides, a fucoid whose entire life cycle is adapted to tolerate low salinities. These adaptations mean that other species of fucoid can’t compete within the same habitat. Fucus ceranoides is susceptible to high levels of grazing from littorinids to the point of their distribution being limited by them (Norton, 1986). However, the salinity conditions within this biotope mean that littorinids are not able to survive, allowing Fucus ceranoides to dominate. The biological community within this biotope is characteristically sparse and many of the other species have life histories which make them opportunistic, short lived and ephemeral. Such species include Ulva lactuca and Ulva (was Enteromorpha) intestinalis. The only identified grazing species come from the family Mysidae. The characterizing species identified for this biotope are the macroalgae Fucus ceranoides and Ulva lactuca, for without it the biotope would not be present. Other species contribute to the biological composition of the biotope, but are not crucial to its presence.
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