Brown Seaweeds

Brown seaweeds are the most common type of seaweed found on rocky beaches. They normally have a method to strongly attach themselves to rock surfaces.The brown colour of the seaweed is due to the brown pigment fucoxanthin overriding the green pigment chlorophyll. Both pigments are used in the photosynthesis of light, fucoxanthin improving the process when the algae is covered by water.

Each species has its own niche on the shore, the major factors being the amount of time they are left uncovered by the tide and the degree of shelter the beach offers. These niches are often strongly defined allowing the species of brown seaweed found on a beach to be used to zone it, or classify it shelter or exposure level, particularly relevant in the case of the wracks.

The richest area of brown seaweed with its accompanying abundant animal life is the kelp forest. This forest is rarely seen, its fringe only being uncovered with spring tides. The forest is dominated by large brown seaweeds such as kelp. These large seaweeds have strong holdfasts to grip the rock face, but with strong storms even these are ripped from the forest, the seaweeds becoming stranded en masse on the shore. After a storm not only will the seaweed thrown up on the beach, but even the anchorage rock the plant was attached to. This is the only easy opportunity to study these seaweeds.

Species of Brown Seaweeds In Cornwall

      Kelps

       Wracks

      Thongweed Himanthalia elongata  

       Sea Balls Leathesia difformis

      Sea Lace Corda filum

      Japweed Sargassum muticum

Thongweed Himanthalia elongata    

The major distinctive feature of this seaweed is its mushroom shaped disk. The disc is about an inch across. From the disc grows a long branched frond reaching up to 6 feet in

length, on which the conceptacles form. The frond is eventually detached, leaving the disc behind.

Sea Lace Corda filum    

Long boot lace like seaweed attached to the sea floor, by a holdfast with fronds easily reaching twenty feet in length.

The fronds are flexible and very tough, tending to become hollow with age. They are slimy and covered with small hairs.

Sea Balls Leathesia difformis   

Now and again small ball like seaweeds get washed ashore. These are Leathesia difformis a stalkless epiphyte.

This epiphyte fastens itself to rocks and other seaweeds.

Japweed Sargassum muticum

Introduced from the Pacific it is thought to have been imported with oysters by accident. This fast growing seaweed is a threat to some native flora which it out competes. It has been in British waters for less than forty years, and it has already got a strong foothold in Cornwall.

Their branched fronds reach a meter in length. The branches have flotation bladders and receptacles.

Flotation Bladders