Rocky Beaches

Rocky shores are the coastal habitats with the most abundant shore life. They are interesting as many of them display a distinct zoning. However the type of fauna and flora that comprise the zoning depends on to what degree the beach is exposed to the elements. The flora fauna noted here are only the most common, there are a plethora of others, but they are too numerous to list.

The following notes attempts to categorise the fauna and flora on the grounds of the level of exposure from the elements a beach receives. It must be remembered that there are only three levels stated here, which in the real world most beaches will not exactly match, instead they will fall somewhere inbetween these levels.

Exposed & Semi-Exposed Rocky Beaches

Supralittoral Fringe

Any animal that lives in this zone has to be tough and be immune to long term desiccation.

Found just above the barnacle zone, lichens are found particularly two black ones, Verrucaria and Lichinia pygmaea. At first sight they will look like oil or tar thrown up on the rocks.

Lichens in The Supralittoral Fringe

Commonly found crawling around the rocks is a small crustacean the common sea slater Ligia oceanica. This animal looks like a rather large woodlouse.

The small periwinkle Littorina neritoides is very common on both exposed and semi exposed rocky beaches, while the rough periwinkle Littorina saxatilis joins it on semi exposed beaches.

Upper Littoral Zone

This zone is dominated by barnacles which are one of two species Semibalanus balanoides or Chthamalus stellatus. Which barnacle species is dominant depends on the conditions. Balanus balanoides is a northern barnacle and in Cornwall it is on the edge of its range. While Chthamalus stellatus is a southern species and find conditions in Cornwall more to its liking and out performs it’s rival and is the dominant barnacle. If both species are found on the same beach, Semibalanus balanoides will be grouped together and can be distinguished by their whiter colour.

Mid Littoral Zone

Barnacles persist strongly into this zone and can still be the dominant animals, but if the beach is exposed, the common mussel will fill their niche instead. The common mussel Mytilus edulis can be so closely packed that their growth is affected and they grow misshapenly. Often stretched out over the mussel beds is the purple laver Porphyra umbilicalis, which when desiccated is coloured black. If either barnacles or mussels dominate, there is one predator that thrives on both and will be found here, the dogwhelk Nucella lapillus .

On exposed shores the bladderwrack Fucus vesiculosus can be found in the form Fucus vesiculosus linearis. This is a bladderless stunted form, that often suffers badly from the severe wave action. The lamina may be worn away leaving only the mid rib and even when the plant does grow back it may lead to a distorted form.

Limpets are found on all rocky beaches whether exposed or sheltered. Three limpet species can be found, the Common Limpet Patella vulgata, the China Limpet Patella aspera and the Black-footed Limpet Patella depressa a southern species. Even if the all the species are found it is almost impossible to determine the species without dislodging them and observing their foot. Limpet shells tend to be flatter on unsheltered beaches or those with strong currents, thus providing the shells a lower resistance to the water flow.

Beadlet Anemones Actinia equina and Snake-locks Anemones Anemonia viridis are the found in this zone. Beadlet anemones are particularly common whether in the rock pools with their tentacles extended or exposed on rocks with their tentacles withdrawn. Snakelock anemones do not favour exposed beaches.

Lower Littoral Zone

Beadlet anemones, snakelock anemones and limpets persist into this area. The Coral Weed Corallina officinalis is common in the rockpools. This bushy red seaweed is distinctive to the feel, it is rigid due to calcium within its structure.

Sublittoral Fringe

This area is only uncovered at really low tides. It is dominated by large brown seaweeds. Investigating this zone is not for the faint hearted as it is very slippery and awkward to move in.

This forest of large brown seaweed composition differs depending on the exposure of the beach. On exposed beaches murlin Alaria esculenta occurs while on less exposed beaches furbelow Saccorihiza polyschides and tangle weed Laminaria digitata.

Sheltered Rocky Beaches

The most important factor with increasing shelter, is the growing dominance of seaweeds that comes with it.

Supralittoral Fringe

The fauna and flora is similar to that of exposed beaches. The height of the zone is less due to reduced wave action having the knock on affect of less splash and spray.

Upper Littoral Zone

Under sheltered conditions, the competition for space is between the barnacles and seaweed. The barnacles tend to lose out. It does not mean that barnacles are not present, they can be still in large numbers,  its just that their absolute dominance has been lost.

The dominant seaweed is the Channelled Wrack Pelvetia canaliculata, which due to its position high up on the beach has to able to tolerate desiccation. If seen on a hot summers day, channel wrack appears to be dead, looking black and completely dried out. However it recovers when recovered by the tide. Often merging with channel wrack is the Egg Wrack Ascophyllum nodosum.

Mid littoral zone

Again the wracks are dominant and cover the rocks. Bladderwrack Fucus vesiculosus is by far the commonest, but is replaced by the more brackish tolerant Horned wrack Fucus ceranoides at places where there is a flow of fresh water such as rivers meeting the sea. In Cornwall, the Edible Periwinkle Littorina littorea can be found in their thousands in this zone. They are to be seen in rock pools where their trails in the sediment are so obvious. Lifting a rock can reveal that its complete underside is covered by edible periwinkles.

The bladders of the bladder wrack are just the right shape and size to provide the perfect camouflage for the Flat Periwinkle Littorina littoralis. Common in Cornwall are both the Flat Top Shell Gibbula umbilicalis and the much larger Thick Top Shell Monodonta lineata.

In this zone there is a continual struggle, between the shellfish particulary the limpet with the seaweeds. These animals are grazers, however the wracks once grown are too tough for them and established themselves on the rocks. However in the rock pools the grazers can have the upper hand, which can be to such a degree that the pools are completely denuded of seaweed (excluding Lithothamnia), the only foothold being the seaweed growing on the back of the limpets.

Lower Littoral Zone

The seaweeds in this area still dominate particularly two species, horned wrack Fucus ceranoides on the rocks and the Coral Weed Corallina officinalis in the rock pools. Horned wrack is often plastered with the small, white, coiled tubes of the Spirorbis worm.

Sublittoral Fringe

As with the exposed beaches this will be primarily a kelp forest. The sugar kelp Laminaria saccharina particularly favours sheltered beaches.