Red Seaweed

Gracilaria – Gracilaria

Banded weeds, Ceramium – Ceramium spp.

Tubed weeds, Polysiphonia – Polysiphonia spp.


Appearance:   All are approximately 5 to 16 inches long.

  • Gracilariayellow green to brownish purple, with coarse,rubbery branches.
  • Ceramiumred, branched, with terminal pincers on the end of the branches. Axes and branches have regular banding patterns.  
  • Polysiphoniayellow, pink or black, red, branched, bushy appearance.


Habitat:    Tide pools, lower intertidal, shallow coves, eelgrass beds

Seasonal Appearance:    All year, most abundant in the summer months

Sensitivity to Human Action







Distinguishing Features & Behaviors

            Red seaweed makes up the largest group of algae in the plant kingdom, with more species accounted for than brown and green seaweeds combined. They are almost exclusively marine plants. Although generally found in shallow waters, these seaweeds are able to withstand deep water and low-light conditions. Red seaweeds can occur as large, branched plants or as bushy growths on rocks and shellfish.

            There are many species of red seaweed in the North Atlantic and New England waters, but three species are commonly seen along the shoreline of Narragansett Bay and Rhode Island: polysiphonia, red ceramium, and gracilaria.

            Polysiphonia is the most common genus of red seaweed. The name polysiphonia is Latin for “many tubes”, which aptly describes the structure of the branches. Often called “mermaid’s hair”, polysiphonia is a bushy seaweed, growing in tufts that are yellow, pink, red or black. The top of the seaweed has many branches and feels soft to the touch compared to the coarse, dark bottom of the plant. It occurs mainly in protected shallow waters, often attaching itself to stones, shells, and eelgrass with a holdfast.

            Red ceramium is branched, resembling polysiphonia, but has pincer-like structures at the end of each of the branches. It will grow up to 10 inches long, often occurring in large tufts attached to just about any kind of substrate.

            Gracilaria is another red seaweed, although it can appear yellow green or brownish purple. Gracilaria is a course seaweed, with rounded, rubbery branches. It is common in quiet, shallow waters and is most abundant in the warm summer months. Gracilaria is commonly found floating over muddy or sandy Bay bottoms.

Relationship to People

            Many species of red seaweed are commonly harvested for food. Usually eaten raw or dried, red seaweed is used in salads, soups, and sushi. Gracilaria is harvested to make agar, a compound user in medical and biological research to culture bacteria and yeast. Agar is also used in the production of cosmetics and hand cream.