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.

Rockpooling destination: Land's End Peninsular, September 2013

Revisit of Land’s End Peninsular

The bay experiences a dynamic regime, alternating between periods of erosion and deposition. The underlying substrate is boulders, however, variable amounts of sand may be deposited on top, sourced from the sand bar situated offshore. The communities encountered reflect the alternation between these regimes.

At the time of visitation the beach was mainly sand with boulders exposed in the region of the river and amongst out cropping bedrock in the mid to lower shore.

Steep cliffs surround the bay, craggy edges of which are covered by lichens. Below, large swathes of sand cover the shore through which a fresh water river has eroded a channel to the sea. Steep sloping bedrock and cliff bases of the mid and lower shore are covered by barnacles, limpets, periwinkles and whelks. Boulders and bedrock of the mid and lower shore host a similar barnacle community plus a variety of seaweeds, including where sand scour is event, ephemeral seaweeds. Throughout the mid and lower shore rockpools occur.

The shore is comprised of bed rock and boulders over which sand has been deposited. A river brings fresh water onto the shore and erodes the sand to reveal the boulders beneath and a succession of strandlines mark the recession of the lowering tide. Habitat classification: LR.HLR (High energy littoral rock), LR. MLR (Moderate energy littoral rock), LS.Sa (Littoral sand) and LS.Sa.st (Strandline).

Habitats classification:

Substrate	LR (Littoral rock)									LS (Littoral sediment)
Habitat	LR.HLR (High energy littoral rock)	LR.MLR (Moderate energy littoral rock)			LR.FLR (Features of ilttoral rock)					LS.LSa (Littoral sand)
Biotope complex	LR. HLR.MusB (Mussels and/or barnacles on high energy littoral rock)	LR.MLR.BF (Barnacles and fucoids on moderately exposed shores)			LR.FLR.Rkp (Rockpools)		LR.FLR.Eph (Ephemeral green or red seaweed communities	LR.FLR.CvoV (Littoral caves and overhangs).	LR.FLR.Lic (Lichens on supralittoral rock)	LS.LSa.St (Strandline)
Biotope		LR.MLR.BF .FspiB (Fucus spiralis on full salinity exposed to moderately exposed upper eulittoral rock)	LR.MLR.BF .Fser (Fucus serratus on moderately exposed eulittoral rock)	LR.MLR.BF .Rho (Rhodothamniella floridula on sand scoured lower eulittoral rock)	LR.FLR.Rkp .Cor (Corallina officinalis, coralline crusts and brown seaweeds in shallow eulittoral rockpools)	LR.FLR.Rkp .SwSed (Seaweeds in sediment- floored eulittoral rockpools).	LR.FLR.Eph.EntPor (Porphyra purpurea and Entomorpha spp. on sand scoured mid to  lower eulittoral rock)
Sub Biotope			LR.MLR.BF.Fser.R (Fucus serratus and red seaweeds on moderately exposed lower eulittoral rock)		LR.FLR.Rkp.Cor.Cor (Corallina officinalis and coralline crusts in shallow eulittoral rockpools)

The communities found were similar to those of the previous visit.

Below are photographs of some of the organisms encountered whilst rock pooling in this habitat.

Fresh water influx cuts a channel through the uppershore to reveal the cobbles below the sand.

Spiral wrack (Fucus spiralis) and ephemeral green seaweed occur on the more sheltered bedrock of the upper shore. Habitat classification: LR.MLR.BF.FspiB (Fucus spiralis on full salinity exposed to moderately exposed upper eulittoral rock).

Small periwinkles (Melarhaphe neritoides) seek refuge within a crevice of the steep faced bedrock which supports an upper shore community akin to littoral fringe biotopes. 

Small periwinkle (Melarhaphe neritoides). 

Representatives of the species complex ‘Rough periwinkle’ Littorina saxatilis agg also inhabit the bed rock. 

Representatives of the species complex ‘Rough periwinkle’ Littorina saxatilis agg. 

Representatives of the species complex ‘Rough periwinkle’ Littorina spp. 

In the cervices of the steep sided cliffs in the mid and lower shore barnacles, common mussels (Mytilus edulis) and Limpets occur. The barnacles and mussels characterise the biotope complex LR.HLR.MusB (Mussel and/or barnacle communities).

Within the barnacle community small rock pools are colonised by the coralline algae, Corallina officinalis  and Corallinaceae crusts, which, characterise the biotope LR.FLR.Cor.Cor (Corallina officinalis and coralline crusts in shallow eulittoral rockpools).

Where these pools drain into damp crevices coralline algae grow as ‘turfs’. Habitat classification: LR.HLR.MusB (Mussel and/or barnacle communities).

The distribution of fauna in the mid and lower shore is influenced by wave exposure, sand scour, fresh water runoff and desiccation. The result is a patchwork of biotopes that are not distributed evenly down the shore. Here mid shore boulders tops are colonised by barnacles and gastropods, whilst below fucoids occur. Habitat classification: LR.MLR. BF (Barnacles and fucoids on moderately exposed shores).

Barnacles, Dog whelks (Nucella lapillus) and limpets cover the boulder, whilst fucoid seaweeds colonise rock below that occurs at a lower altitude and is thus exposed to desiccation for a lower period of time. Habitat classification: LR.MLR. BF (Barnacles and fucoids on moderately exposed shores).

Barnacles.

Limpets have a low shell profile to deflect the wave’s energy as an adaptation to the wave exposure. 

Where sand is deposited on the boulders fauna are forced to aggregate on the remaining available substrate. 

The tops of fucoids are an indication of the relatively recent sand deposition. 

Fucoids ‘emerge’ from the sand, which has been deposited relatively recent. 

The shore exhibits a mosaic of boulders and sand with the hard substrate colonised by barnacles, fucoids and ephemeral green algae. Habitat classification: LR.MLR. BF (Barnacles and fucoids on moderately exposed shores) LR.FLR.Eph (Ephermeral green or red seaweeds (Fresh water or sand influenced), LS.Sa (Sand).

Between the hard substrate are sandy pools within which seaweed species have colonised available hard substratum. Habitat classification: LR.FLR.Rckp.SwSed (Seaweeds in sediment- floored eulittoral rockpools).

LR.FLR.Rckp.SwSed (Seaweeds in sediment- floored eulittoral rockpools).

LR.FLR.Rckp.SwSed (Seaweeds in sediment- floored eulittoral rockpools).

Serrated wrack (Fucus serratus) covers less exposed boulders of the lower shore and characterises the biotope LR.MLR.BF .Fser (Fucus serratus on moderately exposed eulittoral rock).

Lomentaria articulata and cladophora rupestris form part of the Fucus serratus understory community.

Mastocarpus stellatus forms a mosaic distribution with Fucus serratus. The distribution of Fucus serratus and red seaweeds in this manner is characteristic of the biotope LR.MLR.BF.Fser.R (Fucus serratus and red seaweeds on moderately exposed lower eulittoral rock).

Mastocarpus stellatus forms a mosaic distribution with Fucus serratus. 

In areas of the lower shore where the influence of sand scour is increased sand binder (Rhodothamniella floridula) occurs. Habitat classification: LR.MLR.BF.Rho (Rhodothamniella floridula on sand scoured lower eulittoral rock)

Sand binder (Rhodothamniella floridula). 

Entomorpha sp and Porphyra sp covers boulders in an area of sand scour and fresh water runoff. Habitat classification: LR.FLR.Eph.EntPor (Porphyra purpurea and Entomorpha spp. on sand scoured mid to lower eulittoral rock)  

Sections of the lower and mid shore experiencing sand scour have a community characterised by ephemeral and sand tolerant seaweeds. In this patch the green ephemeral Entomorpha sp covers boulders. Habitat classification: LR.FLR.Eph.EntPor (Porphyra purpurea and Entomorpha spp. on sand scoured mid to lower eulittoral rock)

Porphyra covers sand scoured boulders. 

The ephemeral green seaweed Cladophora rupestris and a flat periwinkle (Littorina sp). 

The ephemeral green seaweed Cladophora rupestris.

Caves in the cliff provide shelter from desiccation and the surrounding biotopes often penetrate into the cave entrance. Habitat classification: LR.FLR.CvoV (Littoral caves and overhangs).

The shaded entrance to the cave supports the red seaweeds Osmundea sp, Lomentaria articulata and Corallinaceae crusts, the green seaweed Cladophora rupestris, beadlet anemones (Actinia equina) and common limpets (Patella vulgata). Many of these species have come from the surrounding Barnacles and fucoids biotope where they occur in the shaded understory, conditions similar to the entrance of the cave.

The shaded entrance to the cave supports Osmondea sp. 

Sand scoured gully on shore