Additional factors that affect the distribution of habitats:

Many environmental factors interact to determine the distribution of habitats across the shore.

Exposure to air, whilst the tide is out also influences the distribution of organisms and hence the distribution of communities and habitats on the shore. Many organisms show behavioural adaptations to reduce drying out whist exposed to the air and will become inactive in a shady location such as a crevice with other individuals, and clamp down their shells or, reduce their surface area by curling up, so that they can conserve as much water as possible.

Anemones close up to conserve water

Crabs bury in the damp sand.

The longer the period of air exposure the more specialised to with stand the physiological stresses an organism has to be, so that only those specific organisms with the advantages adaptions to with stand being out of the water for prolonged period of the time will occur at the top of the beach. That isn’t to mean that these organisms can’t occur lower down, in deed in many cases they do. It’s just that lower down other organisms who didn’t cash in on the ability to with stand drying out developed abilities which made them competitively superior to and more abundant than the upper shore organisms once conditions became more gentile.

Small and rough periwinkles are characteristic higher shore species.

So the nearer the low tide mark you get, the less physiological stress organisms experience due to exposure to air, and instead increased competition for space is experienced. Therefore anything that increases the available space increases the number of species that can co- occur. Seaweeds, boulders, gullies and rock pools all increase space and species diversity.

Under-boulder environments increase the surface area and complexity enabling more species to be supported.

Of all of these rock pools provide the greatest refuge from the reseeding tide as it provides constant emersion, allowing species less adapt at withstanding desiccation to flourish on the shore and it is because of this and the unique communities that rock pools support that they have their own habitat classifications associated with them. As rockpools can occur across a range of wave exposures these habitats are broadly known as features of littoral rock habitats.

Rockpools can act as refuges from dessication.

Salinity and sand scour can also influences the communities found, with areas experiencing reduced salinity characterised by seaweeds such as estuary wrack or in areas of reduced salinity or sand scour, ephemeral green and red seaweeds. 

A ephemeral seaweed habitat influenced by sand scour.