Alexandria Gabb

I say kelp, you say… Slimy? Ask around but I bet that for many “magical” is the last word that springs to mind when you mention kelp. For most, the word conjures up little more than memories of slippery seaweed stacks on the beach or perhaps thoughts of a salty snack. Well, I am here to tell you that there’s more to kelp than what’s washed up on the beach or cradling your sushi roll. Nestled just below the surface of cool, coastal shores lies an underwater forest teeming with life. Kelp forests are complex (and magical!) ecosystems, but sadly, as the saying goes “out of sight” often means “out of mind”.

What’s the difference?

The words “seaweed” and “kelp” are often used interchangeably to describe just about any plant-like critter you might come across in the ocean… so what’s what? “Seaweed” is actually an umbrella term commonly used to lump together a wide variety of marine macroalgae, which are essentially any algae visible to the naked eye. They come in all shapes and sizes but tend to be either red, green or brown meaning we can group them based on their colour. “Kelp” on the other hand is a term specific to brown macroalgae. This incredibly diverse order (Laminaria) is some 112 species strong and grows along rocky coasts in temperate and subpolar regions. They favor clear, cool (5-20C) and nutrient rich waters with ample light for photosynthesis. Kelp get their colour from light absorbing pigments, carotenoids, which mix with the chlorophyll in their tissues to create their distinctive brown colour. While most kelp species are relatively short, species such as giant kelp have been known to reach heights of 30-55m tall, growing an astonishing 2 feet every day!

Do the no plants dance

Now that we know what kelp is, let’s take a closer look at it. At a glance, kelp looks an awful lot like a plant, it seems to have roots, a stem, and leaves, just like a lot of plants on land. While kelp would most definitely take home a prize in a plant look-a-like contest, don’t be fooled. Kelp are NOT plants – they are algae! Though they seem alike, kelp lack the complex structures characteristic of terrestrial plants. Instead of roots, leaves and a stem, kelp have holdfasts, blades and a stipe – all of which help make them uniquely adapted to living life below the waves. Like a root, the holdfast acts as an anchor, helping the kelp sit tight against the ebb and flow of daily tides. Unlike a root however, it does not take up water or nutrients. Instead, all parts of the frond absorb what it needs to survive from the water that surrounds it. The holdfasts give way to the strong but flexible stipe, providing support for the leaf-like blades. Much like the leaves of a plant, the blades absorb and process sunlight to create food by photosynthesis. Having a flexible stipe allows kelp to sway and bend in synchrony with moving coastal waters – picture a more graceful, underwater inflatable tube man. This creates somewhat of an issue, however, as the flexible stipe lacks the rigidity to keep the frond standing upright and the blades close to the sunny surface. The solution? A built-in buoy system! By growing balloon shaped floaties called pneumatocysts (gas bladders) and filling them with waste gases, kelp fronds are able to float upright and position their blades near the surface for maximum light absorption!

Just can’t kelp falling in love with you

Under the right conditions, these incredible organisms can accumulate, transforming otherwise barren rocky shores into luscious underwater jungles called kelp forests. Tiered like a rainforest, they can be highly complex, featuring a canopy, understory and forest floor. The kelp forests of the Eastern Pacific coast offer some particularly iconic examples as well some exceptionally iconic residents (see the familiar face below). Here, key species like giant kelp and bull kelp grow so tall that they actually modify conditions on the coast, reducing wave action, settling sediments and cycling detritus and nutrients. These canopy-forming kelps create a three-dimensional seascape providing countless species of invertebrates, fish and mammals with food, nursery sites and shelter from storms and predators. As if all that wasn’t impressive enough, kelp forests are also carbon super-storers meaning they are vital players in our fight against climate change! Kelp forests and other coastal systems (mangroves, seagrass) are thought to capture 20x more carbon dioxide per acre than forests on land. In fact, kelp forests go the extra mile - positioned further from the coast than mangroves and seagrass, the carbon trapped in kelp forest detritus is more likely to sink down to the deep sea and therefore less likely to return to the atmosphere. 

You maki my heart sing

Fantastical forests aside, kelp is a hot commodity! Every year, 100,000-170,000 wet tons of this macroalgae are harvested from Californian waters alone… but what do we do with it? While your first thought might be the classic maki roll, makizushi is actually wrapped in a red seaweed called Nori. Kelp’s meaty flavour and slightly tougher texture, means it features heavily in many soups and broths in East Asian cuisine. Kelp doesn’t just end up on our plates though. Take a look around your house and I can almost guarantee that kelp is closer than you think. Alginate, a popular kelp-derived thickening agent, is used in everything from food and drink to beauty products and pharmaceuticals. It is regularly added to products like ice-cream, salad dressing and pudding as well as toothpaste and shampoo. 

So there you have it. Kelp is SO much more than slimy beach debris. It’s the habitat building, carbon storing and tooth-paste thickening, algae-extraordinaire responsible for maintaining and regulating cool, rocky shores across the globe.

In Spotlight on Sealife we celebrate the creatures that inspire our love for the oceans and encourage us to fight for their homes. Follow this series to uncover lesser-known facts about well-known marine life, and discover weird and wonderful marine animals that you may have never come across before.

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