The next time you eat ice cream or brush your teeth with toothpaste or paint your living room, keep in mind that you might be using a product that has seaweed in it. That is, you might be using an extract from seaweed called carrageenan. Most likely this came from a red alga including a common one that grows in many parts of the world, namely Irish moss (Chondrus crispus).
Irish moss grows in large populations and is attached to rocks and the substrate by a small disc-shaped holdfast. This alga is a deeply red to purple color though it may be yellowish-green if exposed to direct sunlight for long periods of time. The blades are up to four inches long and dichotomously branched. It usually grows in the lower portions of the intertidal zone.
Like many red algae species the life cycle is complicated. There are three stages to its life cycle. There is a diploid stage called the tetrasporophyte which undergoes meiosis and releases haploid tetraspores. These develop into male or female gametophyte plants. A third stage, the carposporophyte, forms on the female gametophyte and releases haploid carpospores which grow into the tetrasporophyte once again. This series of events is an example of an alternation of generations.
Irish moss is a red alga and not a moss. It was a staple of the Irish diet during the potato famine and Irish immigrants were the first to harvest it in Massachusetts. A large “mossing” industry developed in Scituate, Massachusetts in the mid-1800’s and continued through World War II. The harvesting of Irish moss using long iron rakes was another way of earning a living by the sea. Even today a seaweed pudding is made using Irish moss along with some milk, sugar, salt, and vanilla extract.
There are many commercial and industrial uses of carrageenan. A partial list includes yogurt, beer, puddings, fruit juice, cake batter, pie fillings, and cottage cheese. The thickening agent present prevents ice crystal formation in ice cream. It’s also used in some medicines, cosmetics, paints, body lotions, and paper production.
Irish moss has an extensive distribution and grows abundantly along the Atlantic coastline in North America and Europe. There are several related species found in the Pacific Ocean. It has also been collected in the Mediterranean and Bering Seas. Its appearance may vary from place to place depending on wave action.
Like many other seaweeds it may be home to other species that attach as epiphytes. Small red algae like Ceramium and animals like the tube worm Spirorbus can be found on Irish moss. I have collected my favorite seaweed, the sea potato (Leathesia difformis) on Irish moss. Chondrus does shed its surface layer of cells occasionally which reduces the number of epiphytes. Still, this commercially important seaweed is also one of the more attractive plants of the sea.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.