These amazing ecosystems are abundant in species but disappearing fast.

In many parts of the world, towers of underwater kelp form undulating forests in shallow waters. Sometimes called the rain forests of the sea, these lush beds of seaweed are also disappearing like their terrestrial counterparts.

Between 2014 and 2015 alone, an underwater heatwave caused a nearly 95% decline in Northern California kelp canopies.1 Thanks to similar heatwaves, coupled with pollution, global kelp abundance continues to decline by about 2% every year.2

Found in warm waters around the globe, the underwater ecosystems created by kelp harbor an array of inhabitants. Here's a collection of interesting information about the mysterious world of kelp forests.

1. Kelp Is a Type of Seaweed

Although kelp fronds look a lot like trees, and in groups they are called forests, kelp isn’t even a plant. While they photosynthesize like plants, kelp is actually a type of brown algae or seaweed. In fact, all of the world’s plants evolved from algae millions of years ago

2. Kelps Need Cool Water

Kelp grows in shallow water because it depends on sunlight for photosynthesis.

In general, kelp thrives in water that’s kept between 42 and 72 degrees Fahrenheit.3 At warmer temperatures, seawater’s ability to hold valuable nutrients quickly plummets. Kelps need nutrient-rich water to survive, restricting the seaweed to cool, coastal waters.

3. Some Can Grow More Than a Foot a Day

Under ideal conditions, some kelps can grow over one foot in a single day.4 For the giant kelp (Macrocystis pyrifera), a single kelp can produce hundreds of kelp fronds, the kelp equivalent to leaves. Individual kelp fronds can grow to be over 100 feet long, allowing this kelp species to sit comfortably below the ocean’s surface while still reaping the benefits of the sunshine above.

4. They Grow Along 20% of the World’s Coastlines

Kelp forests are found throughout the world including along the west coasts of North and South America, the southern tip of Africa and Australia, and islands near Antarctica. In North America, kelp forests are found on the Pacific Coast, from Alaska and Canada to the waters of Baja California. Together, kelp forests cover over 20% of the world’s coastlines, or about 570,000 square miles.5

5. Kelps Calm Stormy Waters

Together, the many kelp fronds that make up a kelp forest can help put the brakes on incoming waves. As waves roll over a kelp forest, the densely-packed seaweed creates drag, sapping some of the wave’s energy as it passes through. During storms in particular, kelps can help protect coastlines from the full effects of the ocean’s waves, slowing coastline erosion.6

6. Kelps Lack Roots

Kelps don’t use roots. In fact, they don’t grow underground at all. Instead, each kelp attaches to a rock or other solid structure using a holdfast—a ball-like mass of kelp tissue that anchors the kelp to the seafloor. 

7. They Use Gas-Filled Air Sacks to Float

Underwater, kelp forests stand tall thanks to their floating, gas-filled bladders known as pneumatocysts.7 These gas chambers make kelp fronds buoyant, allowing the seaweed to grow upright towards the ocean’s surface where kelp can receive more of the sunlight it needs to proliferate.

8. Kelps Are Sensitive to Warm Water

Kelp forests are particularly susceptible to underwater heatwaves. Warmer water carries less of the nutrients kelp needs to survive and puts added stress on the seaweeds metabolism.

During a particularly long underwater heatwave between 2014 and 2015, Northern California’s kelp canopies declined by nearly 95%.1 Climate change is expected to increase the frequency of underwater heatwaves, putting the future of the world’s kelp forests at risk.8

9. They Form Natural Rafts

When strands of kelp break loose, they have a tendency to clump together and form floating rafts. The raft along with the small sea creatures it carries can travel hundreds of miles, bringing species to new places.9 Scientists have even documented the arrival of a kelp raft in Antarctica carrying a bundle of non-native species, generating new concerns over kelp’s ability to spread invasive species to new habitats.10

10. Kelp Farming Is Popular

Kelp is also farmed as a crop. Globally, kelp aquaculture is part of a $6 billion seaweed farming industry.11 Kelp is typically grown near the coast on a series of ropes called longlines. Instead of building holdfasts on the ocean floor, the kelps grow off of the floating ropes.12

11. Kelp Has Many Uses

Kelp is harvested for use in many products including toiletries, like shampoo and toothpaste, and a wide range of foods, such as salad dressings, puddings, cakes, dairy products, and frozen foods. It's even used in some pharmaceuticals. Algin, a sugar found in kelp, is one of the unique components extracted from the seaweed for use in products as an emulsifying agent. In California alone, between 100,000 and 170,000 wet tons of kelp are harvested each year.13

12. It Is Easy To Buy

Dried kelp can be purchased from many grocery stores and health food stores for use in cooking. While the full nutritional benefits of eating kelp are not yet well understood, kelp contains a unique array of nutrients that are rare or lacking entirely from food produced on land.14