Gracilaria is a bright red or dark brown-black seaweed with typical hard 'knobs' where the reproduction cells are located. It is a typical 'summer seaweed'. The large dark form has been very common on the sandbanks in the Wadden Sea since 1995. It also grows in the delta region. You find it in the zone between high and low tide attached to rocks or gravel. Gracilaria is used for making agar, which is important in the scientific world, particularly for cultivating bacteria or fungi.