Pelvetia canaliculata

Pelvetia canaliculata (L.) Dcne. et Thur. (channelled wrack) is a very common brown seaweed (Phaeophyta) found on the rocks of the upper shores of Europe.

Description
Pelvetia grows to a maximum length of 15 cm in dense tufts, the fronds being deeply channelled on one side: the channels and a mucus layer help prevent the seaweed drying out. It is irregularly dichotomously branched with terminal, receptacles and is dark brown. Each branch is of uniform width, irregularly dichotomously branched and without a midrib. The receptacles are forked at the tips. It is distinguished from other large brown algae by the channels along the frond. It has no mid-rib, no air-vesicules and forms the uppermost zone on the shore growing at or above high water mark. The reproductive organs form swollen, irregularly shaped receptacles at the end of the branches. The conceptacles are hermaphrodite and borne within the receptacles.

Ecology and distribution
P. canaliculata grows on rocks and forms a zone along the upper shore at the upper littoral zone, it is the highest large occurring on the shores of the British Isles. It tolerates a wide range of exposure conditions. It needs periods of exposure to the air, and sometimes grows so high up a beach that coarse grass and other longshore angiosperms grow among it. If it is submerged for more than six hours out of 12 it begins to decay.

Distribution
Pelvetia canaliculata is common on the Atlantic shores of Europe from Iceland to Spain, including Norway, Ireland, Great Britain, the Netherlands, France and Portugal.