Division Rhodophyta, Red Algae

The majority of seaweed species are part of the Division Rhodophyta, or red algae. They are found in a variety of physical forms, including simple and branched filaments, fleshy plants, and sheets. Some red algae are single celled while others can reach lengths of 2 or 3 metres! Red algae have a unique intercellular structure, which gives them a rubbery, springy quality. You can discover the elastic quality of red algae by giving them a gentle pull. In addition to chlorophyll, red algae contain the pigments phycocyanin and phycoerythrin, which give this group their red colouration. However, the colour of red algae varies, and if the pigment phycoerythrin is destroyed, they may appear purple, brown, green, or yellow. The accessory pigments (phycocyanin and phycoerythrin) of red algae allow them to grow in deeper waters than other algae. Red algae also grow in the intertidal zone.

One group of red algae, called the coralline algae (see picture below), are pink in colour and have magnesium and calcium carbonate in their cell walls. These seaweeds are hard like stones, and were once thought to be animals closely related to corals.

Humans have discovered many different uses for red seaweeds. Two substances found in the cell walls of red algae are agar and carrageenan. These are gelling compounds, and are used in food products and scientific research. Carrageenan is an important ingredient in toothpaste and many milk products, such as ice cream and chocolate milk. Agar has many scientific applications in microbiology, biotechnology, and criminology, and is also used in the packaging of canned meats. One of the most popular seaweed food products is a red seaweed called nori (Porphyra), which is used in sushi wraps and other Japanese dishes. Nori is grown in commercial seaweed farms on the east coast of North America and in Asia.

Chondracanthus exasperatus - the turkish towel, and corraline algae in the background

Chondracanthus exasperatus is a simple unbranched plant with one or more broad, thick blades. The stunning blades are brick red to purple in colour, and appear iridescent when wet. This radiant red seaweed is also known as the turkish towel because the surfaces of the blades have a towel-like appearance and texture. Each brilliant blade is covered with numerous stiff projections, called papillae, which may be vegetative or reproductive structures. The beautiful blades can grow up to 1 metre long and 30 centimetres wide. Chondracanthus exasperatus has a short stipe and a disc shaped holdfast, which ranges in diameter from a few millimetres to several centimetres.

Chondracanthus exasperatus grows on rocks in the low intertidal zone and subtidally to 20 metres depth. This beautiful seaweed is found along the Pacific coast from Alaska to Mexico in wave sheltered and exposed areas. The big blades of Chondracanthus exasperatus are also often seen washed up on the beach after storms.

The life cycle of Chondracanthus exasperatus is described as an isomorphic alternating generations life cycle. This means that the gametophytes (gamete producing blades) and sporophytes (spore producing blades) look the same. The word isomorphic means "same form".

The cells of Chondracanthus exasperatus contain a seaweed gum called carrageenan. Carrageenan is an extremely useful emulsifier that is used in numerous food and industrial products. It is commonly used as a thickener in many tasty milk products, such as chocolate milk, cottage cheese, and ice cream, because it gels in the presence of calcium ions. Carrageenan is also found in pasta, pet food, pancake syrup, and toothpaste. Turkish towel blades are also used by humans as wash cloths to remove dead skin.

see more about intertidal Rhodophyta!

References

Druehl, L. 2000. Pacific Seaweeds. Harbour Publishing, Madeira Park, B.C., Canada.

Harbo, R.M. 1999. Whelks to Whales Coastal Marine Life of the Pacific Northwest. Harbour Publishing, Madeira Park, B.C., Canada.

Waaland, J.R. 1977. Commom Seaweeds of the Pacific Coast. J.J. Douglas Ltd., Vancouver, B.C., Canada.

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