The Supralittoral coastal biome marks the landward extent of the transition from marine to terrestrial biomes. It is elevated above the direct influence of waves and tides (see the Shoreline biome) and beyond the direct influence of freshwater seepage or rivers (see brackish tidal biota). Supratidal coastal ecosystems extend around all the world’s land masses, occupying a fringe from tens of metres to a few kilometres wide and covering the entire extent of many small islands.

Onshore winds, created by differences in air pressure related to the differing heat capacities of water and dry land, are a key driver of ecosystem function. These winds create desiccating conditions on elevated landforms such as headlands and coastal dunes, as well as continual inputs of aerosol salts and salt spray. Even though the supralittoral zone is located above high spring tide, it is exposed to recurring disturbance from storms producing exceptional waves and tides that reduce standing biomass and destabilise substrates.

These strong environmental gradients select for a specialised, low-diversity biota. Much of this biota is confined to supralittoral ecosystems and nowhere else, a key feature of these ecosystems, although it may be widely distributed behind shorelines on different land masses due to dispersal by coastal winds, oceanic currents, and/or migratory behaviour. Autochthonous energy is produced by wind-pruned vegetation with traits promoting tolerance to desiccation, high salinity, and substrate instability (e.g. stomatal regulation, extensive rhizomes or root systems, and succulence). The sea supplies allochthonous energy subsidies such as wrack and guano but also transports a portion of primary production to other ecosystems. Invertebrate detritivores and physical weathering contribute to rapid decay. Supralittoral ecosystems also provide nesting habitat for seabirds on the surface, in vegetation or in burrows, especially on islands free from terrestrial mammalian predators.