Towers of underwater kelp form undulating forests in shallow waters in many parts of the world. Sometimes called the rain forests of the sea, these lush beds of seaweed are also disappearing like the jungle forests. In fact, rising sea temperatures along the coast of Australia have wiped out more than 60 miles of kelp forest, making it the most rapid and extensive kelp loss ever documented, according to a new study released in the journal Science.

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

1. Although it looks a lot like a tree, kelp is actually a type of brown algae or seaweed. Kelp belongs to several species of the order Laminariales.

kelp forest Kelp can grow as much as 18 inches in one day. (Photo: NOAA's National Ocean Service/Flickr)

2. In ideal conditions, kelp can grow up to 18 inches per day, according to National Ocean Service, which is part of the National Oceanic and Atmospheric Administration or NOAA/ That's why it can seem like a kelp forest can almost pop up overnight. Kelp can often grow as high as 150 feet underwater.

3. 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, reports NOAA.

sunlight streaming onto kelp Kelp grows in shallow water because it depends on sunlight for photosynthesis. (Photo: worldswildlifewonders/Shutterstock)

4. Kelp is most often found in cool, shallow, nutrient-rich water. Kelp forests grow in water that is between 49 to131 feet deep, according to NOAA. That's because kelp depends on light for photosynthesis.

5. Many living things find shelter or food in kelp's blades. Many use kelp to hide with their young from predators or to weather the turbulence of storms. According to NOAA, among the many mammals and birds that use kelp for shelter or feeding include seals and sea lions, whales, sea otters, gulls, terns, snowy egrets, great blue herons, cormorants and shore birds.

6. Kelp doesn't have roots. Instead, it uses something called holdfasts to attach itself to solid structures such as rocks, reports the National Park Service. Holdfasts act like roots, but they don't absorb nutrients.

bladders on kelp Gas-filled bladders on kelp help keep the fronds floating in the water. (Photo: Ethan Daniels/Shutterstock)

7. Many species of kelp have pneumatocysts, which are gas-filled bladders that help keep the fronds afloat in the water.

8. Summers that are warmer than normal can be harmful to kelp forests, according to Oceana. In addition, very strong storms can wipe out large areas of kelp forest by ripping the plants from the seafloor. Sea urchins are also a danger because big groups of sea urchins can prevent the plants from growing large enough to form forests.

pollution and kelp Pollution can destroy kelp forests. (Photo: Phineas Gage [CC by 2.0]/Flickr)

9. Kelp forests can also be damaged by destructive fishing practices, coastal pollution and accidental damage caused by boat entanglement, according to Oceana.

10. Kelp is harvested for use in many products including shampoos and toothpastes, 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 is extracted from kelp and used as an emulsifying agent in these products. Between 100,000 and 170,000 wet tons of kelp are harvested just from California waters each year, according to NOAA.

11. Kelp is also farmed as a crop, part of a $5 billion global seaweed-farming industry. Kelp absorbs CO2 from seawater, helping fight climate change while also making nearby water less acidic. That's why many kelp farms also raise shellfish, since less acidity creates a better environment for shell growth. By growing kelp and mussels on floating ropes, which also support baskets of scallops and oysters, a farm can produce 40 metric tons of kelp and 1 million bivalves per hectare per year.

12. You can buy kelp, sometimes called kombu, at some health food stores or grocery stores. It's low in calories and high in calcium and vitamin K, according to SF Gate.

Editor's note: This file has been updated since it was originally published in July 2016.

Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science and anything that helps make the world a better place.

12 things to know about beautiful kelp
Found worldwide, kelp forests offer shelter and food to many living things, but in many places, they are disappearing.