There are many kinds of brown seaweeds with different shaped blades. Many rock platforms are covered in brown seaweed called King Neptune’s necklace. The rows of rounded airbladders are stuck together like a large beaded necklace.
The largest seaweeds like kelp are brown seaweeds. These large brown seaweeds have a special structure called a holdfast that is glued to rocks.
The light fades in deeper water. In deeper water brown and red algae are able to use their extra pigments to make better use of the available light.
You can find many types of seaweeds washed up on a beach. As brown seaweeds die they become darker brown or even black. Collect the different dead seaweeds on the beach and compare their size, shape and colour. Are you able to find any holdfasts and bladders?