Red algae gleam in various forms and hues

Gleaming algae in different shades of red can be found on almost every rocky surface within the sunlit zone. Red algae grow a little deeper than other algae, clearly colouring the underwater landscape and occurring up to several metres below the surface. Unlike green and brown algae, red algae can utilise the light which penetrates deeper into the water. Like brown algae, red algae also occur in a wide variety of forms and colours.

Red algae occur at different depths

At shallower depths, red algae usually occur as part of sub-surface filamentous algal zones or among larger kelp species. Small red algae such as Coccotylus truncatus, the stalked leaf bearer, i.e. Phyllophora pseudoceranoides, and the mat-like Hildenbrandia rubra are often hidden on stone surfaces or the stems of wrack species and are easily overlooked.

Of the filamentous red algae, the most commonly occurring species belong either to the genus Ceramium or to the so-called siphon weeds, i.e. Polysiphonia. These form wave-swept, whisk-like and tufted growths amongst other the filamentous algae, as well as on the surfaces of larger algae. Moving deeper, the light decreases and the algal vegetation changes to bare rock surfaces and blue mussel communities, to which the red algae bring a touch of colour.

 Red algae and blue mussels on stone
The beautiful red algae thrive at greater depths than the green and brown algae and can occur as deep as ten metres.

Clawed fork weed is the largest of the red algae

The largest species of red algae in Finnish waters is the clawed fork weed, i.e. Furcellaria lumbricalis. This species occurs as growths of branching twigs on hard surfaces, usually at depths from three to seven metres. These curled plants may reach up to 20 centimetres in length and provide shelter and food at depths from which other algae species are almost completely absent.

A wide variety of invertebrate animals find shelter within the foliage of the clawed fork weed. Similarly, smaller species of red algae can be found hidden in the shade of the sturdier plants as they press close to the bottom. Blue mussels also thrive in such habitats.

Most of the red algae on the Finnish coast come from the saltwater of the oceans. Therefore, the occurrence of these species decreases as one moves north: only two species of red algae, i.e. Ceramium tenuicorne and Hildenbrandia rubra are found at the innermost reaches of the Bay of Bothnia.

 Red algae Furcellaria on stone
Although the clawed fork weed resembles coral, it belongs to the red algae.

Red algae species:

  • Fin. Töpöpunaröyhelö ”Stubby red frill” (Coccotylus truncatus)
  • Stalked leaf bearer (Phyllophora pseudoceranoides)
  • Fin. Meripunakalvo, ”red sea-membrane” (Hildenbrandia rubra)
  • Siphon weed (Polysiphonia spp.)
  • Clawed fork weed (Furcellaria lumbricalis)
  • Fin. Punahelmilevä, ”red bead alga” (Ceramium tenuicorne)
  • Fin. Purppurasamettilevä ”Purple velvet alga” (Rhodocorton purpureum)