Sargassum johnsonii facts for kids

Sargassum johnsonii is a type of brown seaweed. It belongs to the Sargassum family. This special seaweed only lives in one place: the Three Kings Islands in New Zealand. When a plant or animal only lives in one specific place, we call it endemic.

People sometimes call it totara weed. This is because it looks a bit like the leaves of the native New Zealand totara tree. The scientific name, Sargassum johnsonii, honors the person who discovered it. His name was Magnus Earle Johnson. He was an explorer of the Three Kings Islands. He also captained a yacht called Rosemary. He helped scientists visit the islands many times.

Where Does Sargassum johnsonii Live?

Sargassum johnsonii grows on rocks. It lives in the intertidal zone. This is the area of the coast that is sometimes covered by water and sometimes exposed to air as the tide changes. It can also grow deeper, in the subtidal zone. This means it lives underwater all the time, sometimes as deep as 40 meters.

This seaweed is very important for its home. It is a foundation species. This means it creates the main structure of its habitat. Because there is so much of it around the Three Kings Islands, it makes many small homes. These tiny homes are called microhabitats. Many other sea creatures live in these microhabitats. These include bryozoans, sea squirts, and sponges.

What Does Sargassum johnsonii Look Like?

Sargassum johnsonii plants are usually quite large. They can grow to be about 50 to 60 centimeters tall. The main stem of the plant is usually bare and has a bumpy, knobby feel.

The leaves near the bottom of the plant are long and strap-shaped. They can be simple or have small lobes. Their middle vein is not very clear. The leaves higher up on the plant are smaller and narrower. They also have a faint middle vein.

The plant attaches itself to rocks with a small, flat disc. This part is called a holdfast. The whole plant, called the thallus, is dark brown. It feels tough and leathery.

Unlike some other seaweeds, Sargassum johnsonii does not have air-filled sacs. These sacs are called air-vesicles and help some seaweeds float. Its reproductive parts are called receptacles. They are small and swollen, about 2 millimeters long. They grow in clusters where the upper leaves meet the stem.

See also

In Spanish: Sargassum johnsonii para niños