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The Seashore

Encrusting red algae

Encrusting red algae

A number of red seaweeds may be encountered on the shore that appear more like stone, for example Lithothamnion and Lithophyllum.

These calcareous red alga, i.e. species that have depoists of calcium carbonate in the form of calcite or aragonite crystals in the tissues, encrust on the rock. They look like the rock and not at all like an alga. They are invariably asymmetrical, with no fixed shape. The calcite is deposited specifically in the cell walls of these species. The body of these encrustations may cover huge areas of rock from the middle shore to the sublittoral region. They are sometimes mistaken for coral especially as their growth binds stones and rocks together. Those highest on the shore will be pink or even white where they have been bleached by the sun. They become much darker as you go to the lower shore, so the rock looks a deep red colour. In areas exposed to the sun the edges are often bleached white. Due to the rock like consistency they are resistant to grazing and living under other algae they are very tolerant of the shade. They can photosynthesise in very low light and cope with the severest wave action. Encrusting calcareous species often cover the floor of rock pools and moist crevices. Plants can be long-lived although the deposition of so much calcite in the cell wall will ultimately reduce light entering the cell and kill it.

Found in the middle and lower zones of rocky seashores, especially where there is wave action. Dispersed along the European coastline from the north Atlantic to the Mediterranean.

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