Seaweeds are marine algae rather than plants. They have no roots, flowers or seeds; many attach to rock with a holdfast and use flexible blades to capture sunlight and nutrients from the surrounding water.

Large brown seaweeds such as golden kelp, giant kelp and southern bull kelp create layered underwater forests. Their canopies provide food, shelter and nursery habitat, while smaller red and green seaweeds add further colour and structure below.