What is a kelp forest, and why are they important?

Kelp forests line about a quarter of the worlds cold and temperate coastlines, thriving in cold, nutrient-rich waters. These coastal habitats support a surprising diversity of sea life and are one of the oceans most diverse ecosystems according to Oceana, but there is more to these underappreciated ecosystems than meets the eye.

In my latest blog for WorkingAbroad, I wrote about the Great African Sea Forest, the only giant bamboo kelp forest on the planet. It stretches for over 1000km from Cape Town to the coastline of Namibia, and was catapulted to the headlines after the release of the Sea Change Project film My Octopus Teacher at the end of 2020. Here I wanted to dive into the biology and structure of the kelp itself and the environmental benefits protecting seaweed can have in a world in the midst of biodiversity and climate crises.

What is Algae?

Despite its appearance, kelp is not a plant but algae. The term “algae” covers many different organisms, and while they are not necessarily closely related there are features that unite them, such as the ability to conduct photosynthesis. You’ll likely be familiar with a few types of algae, such as seaweeds (like kelp or phytoplankton), pond scum or the algal blooms in lakes.

Believe it or not, you’ve almost definitely eaten seaweed in one way or another. Alginate is derived from its cell walls and has uses across many industries due to its characteristic of forming heat-stable gels. It’s used in anything from thickening ice cream to foam stabilisation in beers.

Algae are different to terrestrial plants in a couple of ways: they lack a true root system, stems, leaves, and a vascular system to circulate nutrients and water around. Algae are also unusual in the fact that they didn’t all descend from a common ancestor, so they form a more informal group which often includes cyanobacteria. Some species exist as single microscopic cells, others, like kelp, take on a leafy appearance.

There are three main types of algae, red, green and brown. Kelp is a type of large, brown algae, and there are four species found in the Great Africa Sea Forest: sea bamboo (Ecklonia maxima) and split-fan kelp (Laminaria pallida) dominate, while bladder kelp (Macrocystis pyrifera) and the spiny kelp (Ecklonia radiata) are less abundant.

Sea bamboo is the largest of these, growing to heights of 17m, creating the canopy that is visible from the shore. While the split-fan kelp only grows to a few metres, it creates the second dense layer of the ‘forest’, a sanctuary for many animals.

At their base, a root-like structure called a holdfast does exactly that, anchoring the rest of the kelp to the ocean floor. The holdfast does not absorb nutrients as a root system would do, but simply anchors the kelp.

A stem-like structure called a stipe extends from the holdfast. The stipe of sea bamboo is hollow and gas-filled, ending in a bulb-like float called a pneumatocyst. The gas content can vary but are usually filled with oxygen, nitrogen, and carbon dioxide. Depending on the species, the kelp may contain one large pneumatocyst or several smaller pneumatocysts distributed throughout the kelp. Split-fan kelp lacks these buoyant structures (though its stipes are often hollow) so it doesn’t float in the same way as the sea bamboo.

From the pneumatocysts, primary and secondary blades emerge which look like leaves. The secondary blades of the sea bamboo can reach 3m in length. From the stipe of the split-fan kelp, it grows a single fan-shaped blade and gains its name from the irregular splits.

Why are kelp forests important?

“I can only compare these great aquatic forests with the terrestrial ones in the inter-tropical region. Yet if in any country a forest was destroyed, I do not believe nearly so many species of animals would perish as would here, from the destruction of the kelp.”

Charles Darwin, 1845

Though Darwin was not referring to the forest off the coast of South Africa, his statement rings true for kelp forests around the world. As ecosystems, they’re as important as coral reefs to the health of the ocean, as well as protecting the coastline from violent storms.

Storing millions of tons of carbon each year when they die and get buried in sediment on the ocean floor, but they’re worth more than just the carbon they lock away. These forests act as nurseries, breeding and feeding grounds for a multitude of animals. Pyjama catsharks cruise through the fronds, getting their name from the stripes that run from head to tail, on the lookout for crustaceans and octopuses to hunt while while brittle stars crawl along the seafloor and jellyfish drift through the green-brown vines. South Africa’s kelp forests are also home to many fish species that aren’t found anywhere else in the world. Blue-grey Hottentot seabream, southern mullet and strepie all live in the forest perpetually, while giant yellowtail and Cape salmon visit to scout out some food.

There are also a colourful array of tiny nudibranchs, ranging from the baby pink of the Verconia protea to the wildly colourful Bonisa nakaza, the Gasflame nudibranch (pictured right). There are an estimated 500 species of nudibranchs in South Africa. Another particularly beautiful sea slug is the sea swallow’s (Glaucus atlanticus) dragon-like translucent and steel blue appearance.

Many species that call the Great African Sea Forest home have yet to be described, but luckily this forest is one of the 27% that are growing, spreading eastwards.

Kelp forests act as a buffer for storm surges, absorbing the brunt of the force of the ocean swells and preventing coastal erosion. The growth of the kelp itself sequesters carbon dioxide and reduces local ocean acidification. There are studies calculating that kelp forests are more efficient at capturing carbon per acre compared to terrestrial forests, so they could be a great ally in the fight against climate change.

Destructive fishing practices, pollution, ocean minings, and chemical waste are just a few of the threats facing sea forests. As well as physically damaging the forest and throwing the delicate balance of species, overfishing can be particularly destructive when targeting urchin-eating species like rock lobsters and abalone. When sea urchin populations boom kelp forests are decimated as they feast on the kelp holdfasts, turning thriving ecosystems into ‘urchin barrens’.

One of the most pressing threats faced by kelp forests is the lack of knowledge and awareness, making it difficult for conservation groups to receive funding for research, advocate for and build momentum for its protection. By sharing its story and voting for change, we can recognise its value.

One thought on “What is a kelp forest, and why are they important?

  1. Great overview of this beautiful ecosystem! I think the fact that they absorb storm energy, protecting coastlines, is especially fascinating. That’s what makes marine science so exciting – the interface between biology & physics is right there. My Octopus Teacher was such a beautiful documentary, but my love of kelp forests was fueled by my own “backyard” aquarium back in the Monterey Bay. They’re doing great work and do a great job of showcasing those sea otters. 🙂


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