Saturday, 9 March 2013

Common Seaweeds of the Shore: Reds




Red seaweeds (Rhodophyta) are the most diverse and species rich group of seaweeds.

Red seaweeds come in all shades from orangey red to pink and can change colour when bleached in the sun or submerged underwater.
Growth forms vary between multi-branched fronds that arise from a stipe, to laminar transparent sheet like forms, to hard encrustations. Even a single species can exhibit a range of morphologies. For example Chondrus crispus can have a flat dichotomously notched frond (not unlike a moose’s antler) or, a thin narrow dichotomously branched frond.

There are over 350 species of red seaweed around the UK, many of which require specialized skills in taxonomy to identify. 

Below are images of some of the common species that you may encounter whilst rock pooling around the UK:

Irish moss (Chondrus crispusis brownish- red to dark red and can be iridescent in water. Growth forms vary from a flat dichotomously notched frond (not unlike a moose’s antler) to a thin narrow dichotomously branched frond.
C. crispus occurs on rock in pools of the lower shore down into the sublittoral.
Grape pip weed (Mastocarpus stellatus) is a dark brownish-red with a flat dichotomously branched frond that can have channels running down it. This species can be easily recognized from seasonal growths that occur over the frond. M. stellatus occurs on rock of the lower shore.
Chondrus crispus and Mastocarpus stellatus
Osmundea spp is brownish-red with a cartilaginous texture, the frond is branched in one plane and looks a bit like a Christmas tree. Osmundea spp occur on damp areas of rock and pools of the mid to lower shore.
Osmundea spp occurring within a crevice. 
Osmundea spp
Corallinacea crusts are one of the most conspicuous red seaweeds of the UK. Crusts form over rocks, shells and other seaweeds as if someone has covered them with pink paint. Corallinacea crusts occur beneath overhangs and understoreys, within rock pools and into the sublittoral.
Common coral weed (Corallina officinalis) looks more like a coral than a seaweed. It is pink with a brittle “crunchy” texture and many joints with pinnate branching in one plane, like a feather. The thinner weed may represent C. elongata.
Corallina spp. occurs on rock within pools and damp crevices.
Corallina officinalis
Corallina officinalis
Corallina sp
Pink plates (Mesophyllum lichenoides) is pink with flat discoid brittle fronds. It occurs on other coralinacea in the lower shore and sublittoral.
False eyelash weed (Calliblepharis jubata) is dark red with narrow blades that branch off from a main stem giving a frilled appearance. C. jubata occurs on rocks and seaweeds in pools of the lower shore.

Dumont’s Tubular Weed (Dumontia cortorta) is brownish-red with long strip like tubular fronds. It occurs on rock in pools of the lower shore and subtidally.
Red grape weed (Gastroclonium ovatum) is brownish-red with a cartilaginous texture and rice shaped branchlets. It occurs in pools of the mid and lower shore.
Red sausage weed (Lomentaria articulata) is red with a limp texture and a beaded growth form. It occurs on rock and seaweeds in shaded areas of the shore.

Lomentaria articulata

Polysiphonia spp is a dark red epiphytic weed that grows predominately on fucoids in the mid to lower shore.


Fine veined crinkle weed (Cryptopleura ramosa) is pinky red with laminar fronds that are irregularly branched with crinkly sides. It occurs on rocks of the lower shore.

Ceramium spp is red with thin cartilaginous branches that appear highly divided and have ends that form pincers. It occurs in pools of the mid to lower shore.

Sand binder (Rhodothamniella floridula) is red and forms dense turfs on sand scoured rock of the lower shore.


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