Brown and red algae
Marine algae range from a few centimetres to tens of metres in length; they grow attached to stones, sand and other objects on the sea floor. Besides chlorophyll their chromatophores contain yellow (carotene), orange (xanthophyll), brown and red pigments, which is why divisions of brown and red algae are distinguished. Brown algae include kelp (Laminaria, e.g. Japanese kelp): large, with the upper part a long ribbon-like blade (several metres) and the lower part a short stalk; it grows from the shore down to about 25–35 m where the water is always moving, and reproduces both asexually (by zoospores) and sexually. Its body holds many vitamins, sugars and other useful substances, which is why it is called “sea cabbage”. The red alga Nemalion and the green alga Ulva are also eaten. In countries such as Norway, Iceland and Scotland algae are fed to livestock; industry extracts iodine and bromine from them; agar from red algae such as Phyllophora is used for marmalade and ice cream and to grow microbes in laboratories.
Demonstration: look at, smell and describe a sample of dried kelp or nori sheet — colour and structure; mark on a map where marine algae live. Tasting only if it is a shop-bought food product, with your parents’ permission (do not eat if you are sensitive to iodine). Safety: never eat algae collected on a shore; wash hands.