Behind the Glass: Sustainable Seaweed Harvesting at the Two Oceans Aquarium

A spotted gulley shark and stumpnose sea bream – two common residents found swimming in the Two Oceans Aquarium kelp forest exhibit.

Sunlight pours in through a three-metre tall window, illuminating the kelp forest in a shimmering green glow. It's like stepping into a secret underwater world, right here in the heart of Cape Town.

Growing up in a land-locked town, and seeing the Two Oceans Aquarium for the first time was one of the highlights of my childhood. But oddly enough it wasn’t the penguins or turtles that caught my attention, but rather the bright colours of the different reefs and seaweeds and the sheer size of the underwater trees in the kelp exhibit.

Seaweed is used in most displays at the Two Oceans Aquarium, yet they mainly go unnoticed. Like sargassum providing horsefish with camouflage shelter (right) and codium acting as a substrate for seahorses to cling onto (left).

The ocean is so much more than fish. It is an entire interconnected ecosystem. Many marine plants like seaweeds are miraculous parts of that ecosystem, sequestering carbon at phenomenal rates, while creating habitats for thousands of other species. And around the world they are on the decline, posing a danger to our existence.

The Two Oceans Aquarium’s mission is to spread awareness about why seaweeds are important, so that people understand their crucial role in keeping our planet alive, and learn to appreciate this resource—and perhaps even be driven to action. But does their educational value justify their significant ecological footprint?

Sourcing seaweeds sustainably

Keeping seaweed happy in a tank is no easy feat. It's like trying to recreate a rainforest in your living room! 

Even though the aquarium tries its best to keep the kelps healthy, it’s impossible to replicate  the ocean conditions where these plants thrive. So, the aquarium needs to constantly replace kelp and other seaweed from wild stocks. 

Collections officer, Matthew, collecting fresh sargassum seaweed to take back to the aquarium. This is then used in displays, the touch pool and as enrichment feeding for rescued turtle hatchlings.

The collections team tries to ensure sustainable practices when collecting their seaweed. They only use hand-harvesting techniques to minimise disturbance, and rotate collection sites to allow enough time for regrowth and to avoid over-harvesting. Smaller and more abundant seaweeds are harvested along the coast weekly, and kelp is harvested monthly. Only 20-30 whole kelps get collected at a time.

According to collections officer Matthew:

“A giant storm will come and wipe out more kelp than we would during a collections trip. I don’t believe we are leaving that much of an impact.”

Thanks, but no tanks

As wondrous and aesthetically pleasing as aquariums are, they have sparked a huge ethical debate. The vast majority of fish you see in aquariums are taken from the wild—including conservation-sensitive areas like the Great Barrier Reef. In the process, fish and other animals are packed into plastic bags and boxes and transported thousands of kilometres. This stressful journey can be too much on their delicate bodies, and many die along the way.

Once they arrive at their aquarium homes, animals must still adjust to captivity. They cannot forage for food as they would normally do in the wild. They may be separated from their family and be unable to create social bonds of their choosing. Aquarium animals have been observed displaying ‘abnormal’ behaviours, including circling, head-bobbing, spiralling swimming patterns and repeatedly touching glass barriers. Health problems include lacerations, wounds, scars, eye disease, deformity, infection, abnormal growths and even death (Rose, 2023).

To have or not to have

There is a huge ethical debate around aquariums, and if the price of education is worth keeping megafauna or any other marine animals in small, enclosed tanks are worth it.

So then is it justifiable to have aquariums at all?

Most of the oxygen we breathe comes from the ocean, and much of it from the seaweeds. Our oceans are endangered by increasing temperatures, acidification and eutrophication, and these dangers pose a threat to our existence. 

Marine life is at the centre of this struggle. Marine plants often sequester carbon much faster than land forests, and are responsible for having checked temperature rise to a great extent. Moreover, seaweeds such as kelp are “ecosystem engineers”, meaning they create conditions for thousands of other species to thrive. These magical creations are in decline all over the world, and many would argue that the first step in fighting this loss is creating greater awareness. 

For those who aren’t lucky enough to dive down and experience the ocean for themselves, aquariums like Two Oceans provide an opportunity to witness the underwater world first hand, and to learn about the ways of the ocean. 

So it’s essential to reflect: How much of an ecological footprint is acceptable for the cost of education and raising awareness? And Is it possible to have aquariums that are truly sustainable?