sandy beach that may comprise a very narrowly defined habitat specifying the key species and sediment grain size ( Lanice conchilega in littoral sand). Thus broadly described habitats can be found in small patches and habitats may not be the best units to describe very large areas.  This notion of scale in defining seabed features has been extended into the concept of marine landscapes (also referred to as seascapes). These are large physiographic features such as estuaries or seamounts, and large areas of seabed defined mostly on their topographic character such as offshore sediment plains. Marine landscapes are discussed further in ' Landscapes and habitats -- different approaches to classification ' later in the MESH Guide.