Red Seaweed Identification

A diverse array of red seaweeds occur within the intertidal many of which require specialist terminology and equipment to identify them. 

The following posts include images of common red seaweed groups and seaweeds that can be identified in the field.

The first step in identifying red seaweeds is to be able to recognize the major groups, then try to recognize the family and note the habitat in which the seaweed is found. 

The most commonly recorded red seaweeds belong to the following orders:

Ahnfeltiales, Bangiales, Bonnemaisoniales, Ceramiales, Corallinales, Gigartinales, 

Gelidiales, Palmariales, Plocamiales,  Nemaliales and Rhodymeniales.

The orders Ceramiales, Corallinales, Gigartinales and Rhodymeniales contain the highest 
 number of common intertidal red seaweeds.

A tree weed - Washed up onto the shore at Great Yarmouth, Norfolk December 2014

Rockpooling Destination: Penberth, August 2014

The shore comprises a narrow cove with boulders lining either side of a slipway. There is a river that forms a small waterfall on the upper shore before flowing beneath the boulders to the sea.

The cove experiences high wave exposure and is characterized by an extended splash zone with lichens and periwinkles, elsewhere barnacles dominate with an increased abundance of limpets and robust seaweeds towards the low water mark. 

These communities fall within the habitat classifications LR.FLR.Lic (Lichens on supralittoral rock), LR.HLR. MusB (Mussel and/or barnacle communities),  LR.HLR.FR (Robust fucoid and/or red seaweed communities) and LS.Sa.st (Strandline).

Whilst rockpooling habitats are most often observed when the tide is out, however, a principle component of their classification is based upon the wave exposure whilst submerged.The following images show examples of habitats in the cove whilst the tide is low and high and demonstrate how the habitats and animals adapt to changes in water level.

Waves crash against the cliffs and boulders. The high wave exposure limits the occurrence of seaweeds in the intertidal, and restricts many organisms to crevices. Only the barnacles that are 'cemented' to the rock avoid becoming dislodged.  Habitat classification  LR.HLR. MusB (Mussel and/or barnacle communities).

Boulders with barnacles and lichina pygmaea.  Barnacles open up to feed whilst the tide is high.

Boulders of the mid shore at low tide with barnacles and robust fucoids. Barnacles are closed to prevent desiccation and fucoid seaweeds become crisp and limp. Habitat classification:  LR.HLR.FR (Robust fucoid and/or red seaweed communities).

The same habitat whilst the tide is in. Barnacles open to feed and the fucoids stand erect supported by air bladders. 

Robust fucoid and red seaweed communities of the lower shore lie flat and limp on the lower shore. Habitat classification  LR.HLR.FR (Robust fucoid and/or red seaweed communities)

As the tide comes in seaweeds such as, thong weed become erect to form a 'forest' above the boulders.

Seasonal growth of ephemeral seaweed form slimy lumps that covers limpets on boulders on the lower shore. Habitat classification  LR.HLR.MusB (Mussel and/or barnacle communities). 

The ephemeral green seaweeds become buoyant, waving too and throw with the waves as the limpets move around.

Large quantities of seaweed accumulate in the cove to form a stand line whilst the tide is out. Habitat classification: LS.Sa.st (Strandline).

At high tide wrasse come into feed on the small crustaceans that feed on this seaweed.