Habitat requirements

Habitat factor Range of conditions
Salinity Full, Variable, Reduced / low
Wave exposure Very exposed, Exposed, Moderately exposed, Sheltered, Very sheltered
Substratum Shingle; gravel; sand

Intertidal sandflats may contain all grades of sand and to a lesser extent silt and clay. The settling velocity of particles is dependent on particle size and water characteristics such that sands and coarse materials settle rapidly and particles >15 µm will settle out within one tidal cycle (King 1975). The gradient of the shore reflects the energy conditions and those of sandy shores tend to be dynamic. Steeper shores are associated with larger grains and shallow profiles with fine sediment (Pethick 1984). Most shores have a range of grain sizes in the swash zone and they are usually composed of fine to medium sand. On a shore with plunging breakers, there is often a concentration of coarser sediment around the plunge at mean water.

Height band Strandline, Upper shore, Mid shore, Lower shore. Intertidal areas by definition have low, middle and high tidal heights and the productivity of these areas differ with respect to the tidal elevation and shore slope (Gray 1981). On sandy shores most of the infaunal community is found on the lower shore. Any increase in height will result in greater exposure to air and thus desiccation of the organisms. Changes in tidal height over the intertidal zone create a less predictable environment where there may be more extreme changes in temperature, salinity, dissolved oxygen and water content than in the sublittoral zone (Hayward 1994).
Zone Supralittoral, Littoral fringe, Eulittoral
Porosity Particle size, mixture and compaction influence the permeability or percolation rate of sands and gravels (Pethick 1984) especially those with a mixture of particles. Porosities in different-sized material may be similar depending on interaction (Taylor Smith & Li 1966).
Water content The water content of sandflats is influenced by the porosity and compaction of the sediment, the shore slope and the potential for draining. The permanent water content in an intertidal sand flat may be low as the interstices between the particles drain during exposure to air, although draining is inversely related to organic and silt content.
Organic content Sand typically has low levels of organic matter and is well oxygenated in the surface layers (Eagle 1973), the organic matter being derived from decaying seaweed, the faeces and remains of animals and terrigenous sources (as wind-blown material).
Oxygen content Oxygen content is a function of the degree of oxygenation (aeration) and the inherent oxygen demand of organic matter. Sands are usually sufficiently oxygenated by seawater which, at high tide, percolates from a few mm in fine, sheltered sandflats to several metres in coarse sand (Eagle 1983). Interstitial oxygenation may be poor below the surface layer particularly where the sand is fine or in cases of high concentrations of organic material such as decaying seaweed on the strand line (Hayward 1994).
Microbial activity Microbial activity is low in areas of higher energy as there is limited organic detritus available for bacterial degradation, coupled with the particles’ comparatively low surface area to volume ratio that provides a surface for microbial populations.

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