The Ocean Basket Kelp Forest Exhibit

Photograph by Karin Schwerm Photograph by Karin Schwerm

An enchanted underwater forest

The Ocean Basket Kelp Forest Exhibit is an underwater forest where kelp plants grow like tall trees, fish swim through the fronds like birds and abalone, sea urchins and rock lobsters feed and take cover among the root-like holdfasts.

Kelp forests are currently only displayed in a handful of aquariums in the world – Monterey Bay Aquarium in California in the United States and here at the Two Oceans Aquarium in Cape Town.

Here, three species of giant kelp provide shelter for an array of local fish, which drift amongst the kelp fronds. Our visitors are mesmerised by the  hypnotic sway of the tall kelp plants and the play of dappled sunlight on silver fish. Central to the "two oceans" theme, this enchanting forest remains one of our biggest drawcards and many visitors return time and time again to its beauty and tranquility.

Kelp forests thrive off southern Africa where the icy Atlantic Ocean washes over rocky and shallow reefs from Cape Agulhas, at the southern tip of Africa, to central Namibia. The southeasterly that buffets the Cape Peninsula in summer causes upwellings of rich nutrients from the cold, dark depths of the ocean. These nutrients fertilise the kelp plants, allowing them to grow into giant forests, the canopies of which can be seen from the shore. 

Four species of kelp grow off our coast, but you are most likely to relate to the sea bamboo, Ecklonia maxima, which is washed onto our beaches by rough seas.

Dive here!

Are you an advanced diver? You can dive in this exhibit.

Photograph by Sven Lennert Photograph by Sven Lennert

Did you know?

  • There are currently 8 500 species of sea plants in the world and more are being discovered every day. Ten percent of the world’s sea-plant species (850) are found only off the southern African coastline. We should be as proud of our sea plants as we are of our famous fynbos!

  • Biodiversity doesn’t stop at the shore – southern Africa has some of the richest flora and fauna in the world, on land and in the ocean. Over and above our indigenous sea plants, we have about 15% of the world’s marine invertebrates on our doorstep and about 16% of our coastal fish are found nowhere else in the world!

  • Sea bamboo is the fastest growing sea plant in the world – the fronds grow at a rate of 13mm per day while the entire plant grows 10mm per day and by up to 400mm in height per month.

  • Kelp plants use holdfasts instead of roots to attach themselves to rocks.

  • Kelp plants absorb nutrients through their fronds.

  • Phytoplankton, tiny single-celled sea plants, produce 90% of the earth’s oxygen! Sea plants play an important role in maintaining the delicate balance between carbon dioxide and oxygen in the atmosphere. With global warming threatening our planet and our survival, we need to protect our sea plants as well as our forests as they provide us with oxygen and absorb carbon emissions from cars, planes and industries.

  • Upwelling off the west coast of southern Africa brings icy, nutrient-rich water from the depths to the surface at a rate of 30m per day. This is a massive amount of water moving towards the surface of the ocean daily. Off Peru and California upwelling only occurs between 1.9 and 2.3m per day. 

  • Capetonians refer to the southeaster wind as the "Cape Doctor" because it "blows away" pollution and "cleans the air".

Fascinating facts about our Ocean Basket Kelp Forest Exhibit

  • It contains 800 000 litres of seawater.

  • The tank it is housed in is 12m x 12m x 6m deep.

  • The water temperature is between 12 and 15º C.

  • The windows are made of acrylic (a type of plastic) and are about 180mm thick.

  • The rocks are made from fibreglass. Sand and crushed shells were blasted onto the fibreglass to make the rocks look real.

  • We pump seawater from the harbour to all our exhibits, including the Kelp Forest. Over and above the water we add every day, we filter 800 000 litres of seawater into the kelp forest every two hours.

  • Three species of kelp are often displayed in our kelp forest – sea bamboo, Ecklonia maxima, split fan kelp, Laminaria pallida, and bladder kelp, Macrocystis angustifolia

Photograph by Sven Lennert Photograph by Sven Lennert

The Kelp Challenge – grow kelp in an aquarium

Like land plants, kelp plants also require certain conditions in which to grow, including sunlight, cool water temperature, wave action, or water movement, and nutrients. 

Sunlight

This exhibit is open to the sky so that the kelp plants can receive sunlight  to photosynthesize.  We have also added strong lights over the exhibit so that we can increase the amount of light on very overcast days and during winter when the sun is lower in the sky. 

Cool temperature

The water temperature in this exhibit must be kept between 12 and 15°C to ensure optimum temperature levels for growth.  This is a challenge in summer and especially when the Cape experiences unusual heat waves.  We have installed large chillers to keep the water temperature within a suitable range.

Wave action and water movement

In the wild kelp plants receive their nutrients from upwelling. During summer, the strong south-easterly wind, which buffets the Cape Peninsula, blows surface water away from the coastline, allowing icy-cold water from the ocean depths to replace it. Wave action and water movement are also vital for kelp growth because they stir up the nutrients and enable the plants to absorb these nutrients through their fronds.

We have installed three systems to increase water movement and the circulation of nutrients in the Kelp Exhibit. The plunger in the far right of the exhibit creates a surge while a streamer pump delivers approximately 70 000 litres of water per hour to create circular water movement within the exhibit. ‘’Dump boxes’’ tip large volumes of water into the exhibit at intervals – this stirs up the nutrients in the exhibit. 

A giant water purifier

Kelp plants thrive on waste products (for example, ammonia) produced by fish.  Together with the biofilter (aerobic bacteria living in the subgravel filter of the exhibit), the kelp purifies the water.  As a result the Kelp Forest Exhibit has the best quality water in the Aquarium.

In fact we use the Kelp Forest Exhibit as a water purifier when algal blooms in the harbour die, turning the water toxic (anaerobic). When this happens, we reduce the amount of water we pump from the harbour and pass it through the Kelp Forest before distributing it to our smaller exhibits.

Collecting kelp at sea

Kelp grows incredibly fast and must be replaced regularly. We often go out to sea to collect kelp from the rocky reefs off Robben Island and Bantry Bay. Divers carefully remove the kelp holdfasts from the rock and swim the plants to the boat. Once on the boat, the plants are placed in a specially designed fibreglass box that has a spray bar and a reflective covering to keep them wet and cool. Up to 15 plants are collected and transported back to the Aquarium where the divers tie them down to rocks in the exhibit.

A forest home for fish

South Africa’s kelp forests are home to many fish species found nowhere else in the world. Some fish, such as southern mullet, strepies and hottentots, live permanently in kelp forests where they find food and shelter, while others, such as Cape salmon, giant kob and even yellowtail, move in and out of kelp forests in search of food.

Our Proudly South African national fish

The galjoen is the national fish of South Africa. Although  it's not a very good-looking fish, it belongs to a family of fish found only off our coastline, so we’re proud of it.

Sadly, our national fish is fast-disappearing – it has been overfished and is now listed as RED by Sassi (Southern African Sustainable Seafood Initiative). Recreational anglers may only catch two galjoen (minimum size of 35cm) per day between March 1 and  October 14 each year. They are not allowed to sell their catch.  

Other South African fish species are in the same boat – overfished and undersized!

When last did you catch a white steenbras this size? Probably not in a very long time! This is because they have been overfished and their nursery areas (mainly estuaries and lagoons) are increasingly threatened by development and effluent. As a result, these fish are no longer caught commercially and it is illegal to buy or sell them in South Africa. Recreational anglers may only catch one white steenbras (minimum size of 60 cm) per day. White steenbras is another RED fish on the Sassi list.

Photograph by Sven Lennert Photograph by Sven Lennert

The many uses of kelp

The South African sea plant industry is worth about R15 million a year – small in comparison to similar industries in the Far East.

Kelp is harvested for use in agriculture, food products, health supplements, waterproofing and to prevent soil erosion.

We also "harvest’’ some of the animals, such as rock lobster and abalone, living in kelp forests. Although the population numbers of these species have declined dramatically, they are still of significant commercial value to the Western Cape.  

Kelp harvesting is carefully monitored in South Africa so that kelp remains a sustainable resource. It is also important that we don’t destroy our kelp forests which are home to many different species of animals.

Long ago kelp was used for:

Storage

The people of southern Africa used dried kelp to store water and whale oil. 

Medicinal purposes

The Topnar people who lived near the Kuiseb River in Namibia dried, roasted and ground kelp into powder, which was mixed with fat and used as a salve to prevent infection and aid the healing of wounds.

Fertiliser

Farmers along the coast used kelp for many years to fertilise their crops.

Today we use kelp in many ways

Agricultural growth stimulant

Kelp is harvested fresh near Kommetjie and taken to Kelpak near Simon's Town, where it is liquidised under pressure to release a growth hormone. When added to normal fertilisers, this agricultural growth stimulant radically increases crop yields. It has been used successfully around the world on wheat, potatoes, olives, grapevines, beans and tomatoes as well as a wide variety of flowers.  

Erosion prevention

Kelp sludge, mixed with seeds, is sprayed on soil embankments to prevent erosion. The kelp sludge acts as mulch, allowing the seeds to germinate and grow quickly.

Waterproofing

Alginic acid, produced by drying and crushing kelp, forms a wide range of salts. Insoluble alginic salts are used to waterproof cement and tiles and to seal fine paper. 

What do these items have in common?

Kelp is dried and crushed to produce alginate, a gel used in these products: toothpaste, ice-cream, pizza-toppings, beer, jelly, salad dressings, flavoured milks, cosmetics, paint and ink. Pet food, dental moulds, clothing dyes and even explosives also contain kelp extracts.

Kelp as a health supplement

Kelp is packed with more vitamins and minerals than any other food! It contains vitamin B2, niacin, choline, carotene and alginic acid plus 23 minerals. Iodine in kelp assists the thyroid gland to function normally while potassium helps to maintain blood pressure. Kelp is also taken for obesity, poor digestion, flatulence and constipation. Kelp tablets can also be given to dogs to treat eczema.

Workers in nuclear power stations are given kelp tablets daily as the alginic acid in the kelp "fixes" radioactive strontium and allows it to be removed from the body.

Food

Kelp and other sea plants are a valued source of food. In Chile, there is a booming trade in "sea vegetables".  Most South Africans don’t eat sea plants, but kelp is harvested to feed abalone, which is grown in farms near Hermanus, Betty’s Bay and Gansbaai.

Make your own jelly

Collect the red ribbon-like seaweed that grows on kelp. Boil it in water to extract a jelly called agar. Add flavouring and let it set in the fridge. Eat it with another product which also contains kelp – ice cream! Yum!