OF SEA BAMBOO, SPLIT-FAN KELP AND BLADDER KELP

Three common kelp species of the Cape Peninsula and west coast.

by Gavin W. Maneveldt, Department af Botany. University of the Western Cape andRene Frans. International Ocean Institute of Southern Africa. University of the Western Cape

The third part in our series on the common intertidal seaweeds of the Cape Peninsula looks at the kelps, the giant brownseaweeds that occur in the subtidal and intertidal gullies of the Cape Peninsula and the west coast. Like trees in an ancientforest, kelp dominate the canopy of the subtidal zone in the cool, nutrient-rich waters of the South African west coast.Kelp is the largest and fastest growing of the seaweeds, growing as much as 13 null in a day. Some of these seaweeds suchas the giant kelp (Macrocystis pyrifera) of central and southern California are known to grow to over 30 m in length.

­20cm

Ecklonia maxima, commonly called seabamboo, occurs abundantly on ilie souili-westand west coasts. It is ilie largest of ilie localkelps, dominating ilie inshore regions of iliesouthern west coast. This seaweed possesses amassive holdfast iliat extends into a long,hollow, gas-filled stipe up to 15 m in length thatends in a bulb (float) at its apex. The bulbfurilier extends into a flat, solid primary blade from which secondaryblades emerge. These seconda'ry blades can quite easily reach 3 m inlengili. Because of its hollow stipe and bulb, this species is buoyed upin ilie water column, its blades frequently breaking the surface ofilieocean. So, when you see kelp at the ocean's surface, this is usuallyE. maxima. This also means iliat E. maxima constitutes the canopy ofthe kelp forest and it is here that three species of red seaweed and thelimpet, Cymbula compressa, occur epiphytically on E. maxima.Photo: G. ManeveJdt. Graphic al1 hy R. Frans adapted frOI11 Ihe artwork by Margo Branch for thebook The Living shores oj southern Africa by George and Margo Branch.

SEA BAMBOO

Unlike most seaweeds that are relatively simplein structure, kelp has reached a level ofspecialization closer to that of the higher

green plants. Because they are so large, these brownseaweeds have developed specialized tissues andorgans. Specialized tissues include conductive tissuefor transporting the products of photosynthesis inter­nally; and reproductive, photosynthetic, andstrengthening tissue. Specialized organs include anelaborate root-like holdfast purely for attachment, astem-like stipe that bears the photosynthetic andreproductive blades, and many possess floats thatkeep the seaweed and its blades erect in the water.All these features have improved the kelps' photo­synthetic ability. allowing them to form extensivebeds that dominate the subtidal zone.

The kelp species common to the Cape Peninsulaand the west coast of South Africa include Eckloniamaxima. Laminaria pallida, and Macrocystis angus­tifolia. Like all brown seaweeds, they also possessthe pigment fucoxanthin which is primarily respon­sible for their colour.

A productive ecosystemEcologically, the kelp canopy provides an importantcomplex, three-dimensional habitat for thousands ofspecies of fish, invertebrates and other seaweeds.The limpet, Cymbula compressa for example, occursonly on Ecklonia maxima. Kelp beds are among themost productive ecosystems on earth, supportinghigh primary production levels. This high produc­tivity forms the base of many coastal food webs incool water environments worldwide. So, bothdirectly and indirectly, they are an important foodsource for a large variety of invertebrates, fish,mammals and seabirds. Furthermore, kelp is toughand resilient, and stretching into the sea, often formany kilometers, it helps to break the force of thewaves offering protection to the nearshoreecosystem.

In South Africa, the seaweed industry is based onEcklonia and Laminaria as well as some other brownand red seaweeds. Kelp is widely used as a fertilizerand is harvested extensively as feed for commer­cially farmed abalone. Ecklonia maxima is used as anutritional supplement for farm animals. It is alsoharvested for the production of a very successfulplant growth stimulant and has been shown to be agreat source of micronutrients.

Internationally, a huge market exists for theharvesting of kelp for alginate production and inSouth Africa, Ecklonia and Laminaria are veryimportant to this industry. Alginate is of consid­erable economic importance as it is used as a gellingand emulsifying agent in a number of industries. Inthe food industry (n'ozen foods, salad dressing,gravies, beer, etc.) it makes water-based productsthicker, creamier, and more stable over extremedifferences in temperature, pH, and time. Similarly,in the cosmetics, pharmaceutical, paint, textile and

38 Veld &- Flora March 2001

20cmSPLIT-FAN KELP

BLADDER KELP

Generallyfound inshallow,somewhatsheltered waterinshore ofE. maximaand L. pallidais the bladderkelp,Macrocystisangustifolia,the leastcommon of the west coast kelps.This kelp is a relatively delicate, vine-like species bearing numerous blades atregular intervals along its slender stipe. At its apex, the new blades are fused,gradually separating as they grow. The blades possess numerous marginal spinesand a single gas-filled bladder at their bases, which allows this kelp to remainafloat and erect in the water column. Unlike the other two species of kelp, anindividual rhizomatously spreading holdfast in this species can bear multiplestipes. Large populations of M. angustifolia are only found at two locations nearCape Town; one at Kommetjie, the other at Robben Island. Unique to this species ofkelp are its haphazardly rippled blades (evident in the upper graphic image).This feature is especially important, as it allows for increased absorption ofnutrients in relatively low flow environments typical of sheltered lagoons or bays.Photo: G. Maneveldt. Graphic art by R. Fn:lI1s adapted [!"Om lhe artwork by Mengo Branch for Ihe book The Liv;ns

shores of southern Africa by George and f\1argo BI'anch.

While the sea bamboo, Ecklonia maxima, is the dominant kelp in inshore waters ofthe southern west coast, it becomes progressively replaced by another kelp species ­the split fan kelp, Laminaria pallida - in deeper waters and also further north upthe west coast. Laminaria pallida lacks the buoyant structures found in E. maxima(although the stipes of occasional plants have been shown to be hollow), so it rarelybreaks the surface in deeper water. It grows to about 10 m in length and possesses asingle broad, fan-shaped blade that becomes irregularly split, giving the kelp itsname, the split-fan kelp. Unlike the sea bamboo which is more common inrelatively shallow water, L. pallida occurs to depths of 30 m. Adult plants ofL. pallida also differ from those of E. maxima in that they have warty stipes asopposed to the smooth stipes ofE. maxima. Split-fan kelp, like seabamboo, is common on wave-exposedshores.Photo: G. Maneveldt. Graphic arl by R. Frans adaptedfrom the artwork b~1 1argo Branch for thf~ book TheLiving shores of southern Africa by George andT\lar!,:o Branch.

welding industries, alginate aids inthe suspension and stabilizing ofagents over ranges of temperature andpH. In the paper industry, forexample, alginate enables sizing andpolishing of the finished paperproduct. Did you know that alginatefrom kelp is even used to make fibresfor audio speakers?

Kelp is especially important to themedical industry. Its alginate is usedto encapsulate many things such astablets in powder form, in fracturecastings and moulds, and even inorgans for transplant. Kelp containsan astonishing amount of vitaminsand minerals, the most important ofthese is probably iodine. Iodine has anormalizing effect on the thyroidgland (this gland controls the body'sgrowth and development). In Namibia,scientists are looking to use Eckloniaand Laminaria as a treatment of goitreand prevention of (or reduction in theoccurrence of) cretinism in southernAfrica. Similarly, because iodine feedsthe thyroid, kelp is used in weightloss formulas. Japanese studies haveeven shown a direct relationshipbetween algin contained in kelp andthe prevention of breast cancer.

Macrocystis angustifolia is not usedin the alginate industry, although ithas been reported to have a higheralginate quality than either E. maximaor 1. pallida; the natural populationsof this species are too small to warrantcommercial harvesting. There are,however, a number of scientificstudies underway on the feasibility ofcultivating species of kelp for alginateextraction. Marine cultivation, ormariculture, could be the answer to asustainable high-grade alginatequality.

While the seaweed industry in theWestern world is based mainly onseaweed extracts, in the East seaweedsare cultivated in huge volumes forhuman consumption. Much of thisindustry though, is based on redseaweed, which is the subject of ournext article in this series. (YI

A beautiful calendar far 2001 an the cammon

seaweeds of the Cape Peninsula is QI'ailable from

the EERV at VIl'e. tel (021) 959 2498.

WHAT DOES THAT MEAN?

Epiphytic living on or attached toplants.Blade synonymous with leaves ingreen plants.Holdfast the root-like organ ofattachment in kelp.Rhizomatous a creeping stem-likestructure.Stipe: the flexible 'stem' inseaweeds.Upwelling cold nutrient-richsub-surface water moves to thesurface to replace offshoremoving surface water, especiallyprevalent on our west coast.

Veld Er Flora March 2001 39