Sargassum is a large seaweed genus which prefers the open waters of the tropics, although some species can be found clinging to rocks closer to shore. Members of this genus are referred to as “Sargassum” by both biologists and laypeople, an example of a situation where the scientific name for something is also its common name. Many people are familiar with the concept of Sargassum, thanks to the fame of the Sargasso Sea, a remarkable feature in the Atlantic Ocean which has been a topic of discussion and commentary for hundreds of years.
Like other seaweeds, Sargassum is a form of algae which has developed a multicellular structure. Sargassum is characterized by long highly branched fronds which can make it appear almost leafy, and many have bladders filled with air which help them to float. In the open water, these bladders keep the Sargassum free floating near the surface of the water so that it can photosynthesize energy. In areas with Sargassum is anchored to the bottom, these bladders help the seaweed stretch towards the light, creating forests of seaweed which gently undulate with the waves.
There are a number of uses for Sargassum. In some regions, for example, it is collected as fertilizer. It is also a food source, especially in Japan, where it may be added to soups and fermented with the other ingredients in soy sauce to create a specific flavor. Many animals call Sargassum home, as the seaweed provides shelter with its abundant fronds, along with a hiding place from predators and a source of food.
The Sargasso Sea is a large section of the Atlantic Ocean which is often covered in mats of this interesting seaweed. Travelers were initially very confused by the region, which looked bizarre with mats of floating seaweed on it which were sometimes thick enough to choke a ship's progress, and they assumed that other than the seaweed, the Sargasso Sea was barren. This is not, in fact, the case. The seaweed hosts a number of animals, and the Sargasso Sea also plays an important role in the development of both European and North American eels, who travel to the area to lay eggs.
Closer to shore, Sargassum often occurs in combination with other seaweeds, creating lush underground forests which are filled with all sorts of fascinating animals. Sargassum is generally dark brown to green in color, with many branching fronds and a slightly sticky texture. You may also hear Sargassum called “gulfweed,” especially in the Southern United States.