OF PURPLE LAVER, TONGUE WEED AND HEDGEHOG SEAWEED

Common red seaweeds of the Cape Peninsula.

by Gavin lIv. Maneveldt, Department of Botany, University of the Western Cape and,Rene Frans, International Ocean Institute of Southern Africa, University of the Western Cape

The fourth part of our series on the common intertidal seaweeds of the Cape Peninsula looks at thered seaweeds, which form by far the largest group of seaweeds on the Peninsula and dominate the mid

to lower intertidal area to a large extent. Like the brown seaweeds, many of the reds are fleshy andbulky and generally occur lower down the shore because they are less tolerant of salinity and

temperature extremes than some of the common green seaweeds.

Veld Er Flora June 2001

Nothogenia erinacea (left) is aptly called thehedgehog seaweed. It consists of elongated leaf­like blades that are tough and leathery when wet,and papery when dry. The blades bear numerousdensely packed tuft-like outgrowths giving theseaweed its hedgehog-like appearance. Thisspecies varies in colour from yellow-brown toalmost black. It is also very common in the mid tolower intertidal zone.

Porphyra species, or purple laver (above and left)are extremely thin (only one cell thick), flat,membranous plants. This seaweed looks like asheet of wrinkled cellophane when dry - allcrumpled and folded upon itself. They vary incolour from yellow to purple to almost black.Porphyra is abundant high up on the shorewhere desiccation stress is at its greatest, and notmany other species can survive. It hasremarkable recovery capabilities - and cansurvive dehydration for a week.

Hildenbrandia lecanellierii, an encrustingred alga (right), is tolerant of the desiccationstress high up on the shore. Lookingremarkably like splashed tar, this speciescovers large expanses in the upper intertidalarea, in crevices and in places prone to sandinundation. Older parts of the plant oftenbecome detached from the substrate, but itrecovers quickly from physical disturbanceand can regenerate from but a few cells.

Red seaweeds appear redbecause they possesspigments known as phyco­

bilins that absorb blue and greenlight and reflect red light.Although they are commonlycalled red seaweeds, some mayappear black, blue, yellow andeven green. This is especially truefor intertidal reds, the redpigments of which may becomemasked by the chlorophyll andother pigments present in them.As blue light penetrates water to agreater depth than any other light,the phycobilins present in redseaweeds allow these seaweeds tophotosynthesize and survive atgreat depths - some as deep as250 m.

The red seaweeds common tothe Cape Peninsula and theSouth African west coast includePorphyra species, Hildenbrandialecanellierii, Aeodes orbitosa,Gigartina polycarpa, Sarcothaliastiriata, Nothogenia erinacea andHypnea spicifera.

Of all the seaweeds, the redsare probably the most economi­cally valuable. The genusPorphyra in particular makes atleast 80 % of all seaweedharvested all over the world. InAsia it is known as nori and iseaten as a whole seaweed eitherdried or in soups, or as tastywrappings for sushi and rice.The iodine and high vitamin andprotein content of nori makes itpopular, as does the relativesimplicity of its mariculture(sea farming), which began morethan 300 years ago in Japan.Red seaweeds are also importantfor their phycocolloid extracts,which cause particles to remainsuspended in solution and aretherefore excellent as stabilizing

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and gelling agents. The mainphycocolloids derived from redseaweeds are carrageenan andagar. Carrageenan is important inthe dairy industry - milkshakes,cheese, yoghurts and powderedmilk (including baby formula)possess red seaweed extracts.Believe it or not, carrageenan iseven used in pet food, cosmetics,shampoos, paints and toothpaste.A number of carrageenophyteseaweeds are being investigated inSouth Africa, including Hypneaspicijera and various species ofGigartina, Sarcothalia andAeodes.

Agar on the other hand, has itsmost important use as a mediumon which to culture fungi andbacteria in microbiological andmedical pathological research. Infood for human consumption agarcan be found in baking andconfectionary products and is alsowidely used to clarify wine, juiceand vinegars because of itsexcellent protein bindingproperties. In larger industries,agar is used to make adhesivesand capsules for tablets. SouthAfrican agarophytes include theseaweed genera Graci}aria(which is harvested extensively inSaldanha Bay) and Gelidium. ~J

There is another group of red seaweedsthat are especially important in theformation of coral reefs. an activity withwhich they have been intimately involvedfor miJlions of year.~. These reef-buildingseaweeds are the encrusting coraJIine rcdseaweeds. which is the .~ubject of my nextand final chapter in thi.~ series.

AcknowledgementsThe graphic art for much of the seaweedseries was adapted from the artwork byMargo Branch in the book The LivingShores of Southern Africa by Margo andGeorge Branch.For information about the authors. seepage 125 of the September 2000 issue ofVeld &' Flora.

Sarcothalia stiriata (right) or twistedgigartina (it was formerly classified underthe genus Gigartina) is a fleshy, rubbery,translucent seaweed that often occurs inequally high densities with Gigartinapolycarpa in the lower intertidal area.There are two distinct forms: asexuallyreproducing individuals are smooth,somewhat flattened and forked at theirapices and sexually reproducingindividuals are contorted (hence thename) into irregularly proliferating fleshypapillae. Both stages often occur side byside on the rocky shore. Colour variesfrom a translucent yellow-green toreddish-brown to almost black.

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Aeodes orbitosa (in centre of photo above,and graphic on top left), commonly knownas slippery orbits., is a tough, flat, slippery,leaf-like seaweed."Colour varies fromyellow-brown to reddish-brown. Thisseaweed is common in the middle tolower reaches of the intertidal area whereit often occurs in large expanses. Insheltered intertidal pools, it can grow to2 m in diameter - you could easily drapesuch a single plant over a standardbedroom door!Gigartina polycarpa (on left and right ofphoto above. and graphic on bottom left).or tongue weed, is a tough, fleshy seaweedwith oval blades. Individuals of thisspecies are characteristicaJly rough andbear numerous papillae (sometimes theblades are even rippled) giving theappearance of a rough tongue. The colourvaries from yellow-brown to reddish­brown to almost black. With Aeodes it isquite abundant in the lower half of theintertidal zone.

Hypnea spicijera, (far left and left)commonly called green tips, occurs asdense green and purple clumps on thelowest parts of the shore and is onlyvisible during low water of spring tides.The upper parts of the clumps are coveredwith numerous short green fleshy spines.The colour in this species is character­istically purple-brown at the base and aluscious translucent green at the tips.The chlorophyll completely masks the redpigment near the upper surface of theseaweed. It is able to form extensive matson the lowest reaches of the shore becauseof its rhizomatously spreading holdfastsystem.

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