Substrate (aquatic environment)

Substrate is the earthy material that forms or collects at the bottom of an aquatic habitat. It is made of sediments that may consist of:

Silt – A loose, granular material with mineral particles 0.5 mm or less in diameter.
Clay – A smooth, fine-grained material made of fine particles of hydrous aluminium phyllosilicate minerals.
Mud – A mixture of water with silt, clay, or loam.
Sand – Mineral particles between 0.06 and 2 mm in diameter.
Granule – Between 2 and 4 mm in diameter.
Pebble – Between 4 – 64 mm in diameter.
Cobble – between 6.4 and 25.6 cm in diameter
Boulder – more than 25.6 cm in diameter.
Other, assorted organic matter, detritus.

Stream substrate can affect the life found within the stream habitat. Muddy streams generally have more sediment in the water, reducing clarity. Clarity is one guide to stream health.
Marine substrate can be classified geologically as well. See Green et al., 1999 for a reference.
Mollusks and clams that live in areas with substrate, and need them to survive, use their silky byssal threads to cling to it. See Cteniodes Ales for reference.