While walking along the beach, piles of kelp can be seen washed ashore. Although this slimy, and often stinky tangled mess is not appealing to look at, it’s extremely
helpful to the planet. Kelp forests cover 20% of the world’s coastlines, equivalent to approximately 1.5 million kilometres, and not only have a phenomenal impact on ecosystems in the ocean but the atmosphere above as well.
Disguised as a plant, kelp is actually not a plant at all! Kelp is extremely brown algae and belongs to a special family known as Protista which is roughly classified into three categories of red, green or brown algae; also known as seaweed. There are thousands of varieties of marine algae within these three categories and they vary greatly in appearance. Kelp refers to large brown algae which will be the primary focus of this article.
What is Kelp
Kelp shares some similarities to plants, performing photosynthesis and having a leafy appearance but is also quite different. Unlike plants, kelp does not have roots to pull nutrients from the substrate, nor does it have a vascular system through which nutrients are transferred. Kelp absorbs all of its nutrients from passing water. Structurally, kelp consists of a holdfast, stipe, blades and gas bladder. Frond is a term used to refer to the blades and stipe combined.
At its base above ground is a holdfast which may resemble roots in appearance. Holdfasts are a mass of tissue used strictly as an anchor attaching to solid structures to prevent floating away. Instead of a trunk or stem, kelp has a stipe which is used primarily for support. Stipes can vary in size and structure depending on the species of kelp, being rigid, flexible, or gas-filled. Finally, kelp has blades instead of leaves which have photosynthetic cells on both sides, whereas most plants only have them on one. This increases surface area to maximize the use of available sunlight for energy and to absorb nutrients from the water.
Varying pigments in marine algae is another way to maximize energy from the sunlight. Different pigments absorb different light waves, for example, green seaweed has primarily green pigment, like plants, which is good for absorbing red wavelengths. Red wavelengths cannot travel very deep in the water though, therefore green seaweed thrives in shallower waters. Kelp and red seaweed also have green pigment, however, kelp has primarily orange and red seaweed contains primarily red and blue pigments. Orange, red and blue pigments are able to absorb the blue-green wavelengths which travel much deeper into the water. These wavelengths are what gives the ocean its blue-green appearance.
Kelp reproduces by releasing microscopic spores through special blades located near the holdfast. Spores will settle on the ocean floor and eventually grow into male or female forms while still microscopic. When mature, the males and females will release their respective sperm or eggs, which then face the challenge of finding one another. Females release pheromones which is a chemical that helps sperm locate the eggs. Once fertilized it will grow into what we recognize as kelp.
Rainforests of the Sea.
Kelp forests are complex ecosystems, providing shelter and food for thousands of sea creatures making it one of the most productive ecosystems in the natural world. Scientists estimate that marine algae also contributes up to 80% of the oxygen available in the atmosphere!
Kelp protects coastlines as well by slowing incoming waves which minimizes erosion. As a wave passes by, a kelp forest creates drag reducing the energy of the wave as it comes to shore. This is especially important during storms. Kelp forests go through seasonal changes like a terrestrial forest, dying off in winter and growing back in spring, with the holdfast remaining to grow again the following season. Kelp lives on average 4-5 years however have been reported as old as 8-10 years.
While most members of the protista family are single-celled organisms, brown algae is more complex, are the largest marine algae, and possibly the fastest growing organism in the world! Giant kelp is the largest species and lives in cold, clear, nutrient-rich waters. On average it can reach 30 meters in length, growing 28 cm per day! In ideal conditions giant kelp may reach up to 53 meters, growing 61cm in a single day! Upon reaching the surface giant kelp continues to grow. This extra growth lays horizontally on the surface of the water creating a raft on which some creatures rest. Sea otters use kelp to wrap themselves up in and have a nap without being swept away to sea.
Rapid growth requires a lot of energy and nutrients, which means access to sunlight is very important. Kelp, being large and heavy, requires assistance to grow upright towards the light. Luckily it’s equipped with a built-in flotation device called a float which is a gas-filled bladder at the base of its blades. Floats differ structurally between species, for example, giant kelp has many blades running up the entire length of the stipe, and located at the base of each blade is a small pear-shaped float. Bull kelp is very closely related to giant kelp and is one of the most common in Victoria. Structurally it only has one set of four blades at the very top of the stipe, with one large ball-shaped float at the base of the blades.
Kelp and Climate Change
Thanks to its rapid growth rate and ability to remove carbon dioxide from the atmosphere, kelp could play an important role in preventing global temperatures from rising further. Coastal ecosystems have the ability to absorb 20 times more carbon than a terrestrial forest! In most cases when kelp dies it gets washed out to deep sea where it will sink to the bottom, and because of low oxygen levels in the deep water, it breaks down much slower, preventing the release of carbon dioxide possibly for centuries! Estimates suggest that approximately 200 million tons of carbon dioxide are removed from the atmosphere by kelp each year.
Although kelp is not yet on the endangered list there is a concern about its declining presence due to human interference. Purple sea urchins eat kelp at exponential rates; otters on the other hand like to eat sea urchins and keep them under control. Unfortunately, humans have played a significant role in the decline of sea otter populations by overhunting. Pollution, combined with overfishing has left remaining otters with a limited food supply, making it difficult for them to bounce back. If sea urchin populations get out of control they create what is called an urchin barren which is like a desert underwater. This happens when the normal food chain is disrupted and imbalanced.
Global warming is also an issue because kelp thrives in cool coastal waters and requires a nutrient-rich environment to survive. Warmer water tends to contain less nutrients and reduces the kelps ability to hold onto these vital nutrients. Between 2014 -2015 heatwaves underwater resulted in a near 95% decline of kelp forests in Northern California. Over the years similar events along with pollution has resulted in kelp declining approximately 2% per year. This is expected to continue unless humans can get climate change under control. Climate change also causes weather extremes. Large wind storms can devastate kelp forests, breaking them off or even washing ashore the entire holdfast which means it cannot reproduce again.
Kelp also has many uses for human consumption and product use which has led to harvesting kelp at increasing rates. This may be one of the greatest threats because of an already imbalanced ecosystem. If kelp goes extinct, thousands of species will suffer. Kelp can help, but humans still need to put a lot of effort into implementing change by minimizing our own carbon footprint.
