Irish moss is a red seaweed found in large colonies on stones and rocks in shallow water. Irish moss is also called carragheen, because it contains so much carrageenan. Carrageenan is used as a thickener and stabilizer in many products, including ice cream and lunch meats. The Scots use this seaweed for making a kind of tapioca pudding. The seaweed is found in the Atlantic Ocean and adjoining waters, such as the North Sea and parts of the Baltic Sea.