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Seaweeds
Various seaweed species can be seen on Chek Jawa

What are seaweeds? Seaweeds are algae that live in the sea or in brackish water. They are considered "large algae" or "macro algae" to differentiate them from the microscopic algae that abound in the same habitats.

Why do seaweeds have such weird shapes? Algae are very different from ‘normal’ land plants. Although both have chlorophyll, algae don't have true roots, stems and leaves. Algae don't have a system of channels to move water around their body, called a vascular system, that 'normal' plants do. So they can only grow in water or moist places. Freed from the 'rules' of living on land, seaweeds can take all kinds of shapes from filaments to sheets, encrusting layers to branching forms.

Although some seaweeds might look similar to seagrass, the body parts of these seaweeds work differently. So they are named differently.

For example, the part that anchors the seaweed is called the holdfast and not the root. The holdfast simply grips the surface and does not absorb nutrients or grow extensively into the ground like true roots.

Caulerpa sertularioides
This seaweed is often mistaken for seagrass. Place your mouse over the photo
to see the names of the different parts
of this seaweed.

The leaf-like portion is called the blade and the stem-like portion that holds it up, the stipe. The whole seaweed is called the thallus. Seaweeds photosynthesise and absorb nutrients and water with all parts of their body.

Freakin Fucus has an excellent simple explanation with diagrams of the various parts of seaweed and the bizarre shapes that seaweeds can take on.

Algae are found everywhere! Algae grow everywher ein the sea, in freshwater and even on land. Large seaweeds grow attached to the ground or hard surfaces. Smaller algae grow on the seagrass or even bigger seaweeds. They also coat rocks, snail shells and other hard surfaces. Invisible microscopic algae float in the water and grow in soil. Algae may also grow inside animals (such as carpet anemones) or other living things (such as with fungus to form lichen).

Why are seaweeds slimy? A slimy coating reduces water loss when exposed at low tide. Being leathery also helps. Seaweeds also protect themselves from herbivores by containing unpleasant tasting chemicals such as iodine.

Seaweed reproduction: Algae do not have flowers, fruits or seeds. Instead, they have a complex method of sexual reproduction involving the formation of some kind of spore. Seaweed can also grow from fragments of the parent plant.

Role in the habitat: Unlike seagrass, seaweeds are eaten by a wide range of creatures from snails to fish, crabs to sea urchins. Small algae that grow on hard surfaces, seagrass leaves and even bigger seaweed provide food for tiny grazers such as snails.

Larger herbivores such as sea hares munch on bigger seaweeds.
Seaweeds can grow very fast. During certain seasons when the waters of Chek Jawa are particularly rich in nutrients, there can be a 'bloom' of various algae. These seaweeds can carpet the shores or get washed up in huge piles on the shore and sand bars.

Human uses: Many seaweeds are edible to humans too. You have probably eaten some seaweed recently! Extracts of seaweeds are widely used to colour, stabilise and thicken food. Some seaweeds are even cultivated for commercial uses.

Colours of the Weed: All seaweeds have green chlorophyll, but some also have other pigments. Seaweed species are classified by their colours.

Green seaweeds (Division Chlorophyta) are usually found closer to shore because they can tolerate more sun and drying out.

Red seaweeds (Division Rhodophyta) can grow in deeper waters where green seaweeds may not survive. This is because their red colour allows them to photosynthesise in lower light levels. The ‘Nori’ used in Japanese sushi is a red seaweed (Porphyra spp.). Red seaweeds are a source of agar used to make delicious jellies (agar-agar); and carrageenans, natural gums used to gel and stabilise food such as chocolate milk and yoghurt.

Brown seaweeds (Division Phaeophyta) are more common in colder waters. They are a source of alginates used to make water-based products thicker, creamier and more stable. For example, alginates make smoother ice cream.

Status and threats: Like other plants of the intertidal zone, seaweeds are affected by reclamation and human activities that result in pollution or increased sedimentation. However, some human activities may actually promote seaweed growth. For example, nutrient rich water from sewage and other outflows might trigger an explosive growth of seaweeds. This, however, can result in an imbalance in the ecosystem.

Huge bundles of seaweed are sometimes washed ashore

Sea lettuce sometimes carpets Chek Jawa's shores

Links
Seaweeds on the OceanLink website: lots of layman information on all aspects of seaweeeds, what they are, how they reproduce, what they are used for.
Gifts from the Seaweed by Donald Cheney, the Seaweed Biotechnology Laboratory on the Northeastern University website: a fascinating but easy-to-read article on the many uses of seaweed and about seaweed agriculture.
Freakin Fucus by Andrew Davies: lots of delightful articles on seaweed ranging from primers for the layman to more technical articles, with an enlightening section on the basic structure of seaweeds, various forms that seaweed can take, and algae communities. Lots of photos and links too.
The Tree of Life on the Museum of Paleontology, University of California, Berkeley website: has introductions to green algae, red algae,
Modern Uses of Cultivated Algae by Steven L. Morton on Ethnobotanical Leaflets on the Southern Illinois University website: lots of information on current uses of macro and micro algae.
Plants and Algae on the Ask-a-Scientist website has lots of interesting questions with equally fascinating answers on seaweeds and algae.
Algae on Life on Australian Seashores by Keith Davey on the Marine Education Society of Australia website: a fabulous goldmine of a site which covers various kinds of intertidal habitats and their inhabitants. An introduction to seaweeds in general with facts and photos on common green, red and brown seaweeds of Australia.
on the Northern Arizona University website:
Welcome to the world of Algae on the University of the Western Cape, South Africa website: with a virtual slide show for beginners, some interesting student assignments including classification of algae, and farming of algae (mariculture). Lots of links to other sites too.
An introduction to carrageenan on the Amer Trading Co. website: lots of details on industrial applications of carrageenans
Why is some ice-cream made with seaweed? Isn't there a better ingredient? on the Mad Scientist website: Robert LaBudde gives a simple explanation of why seaweeds make better ice-cream!
The Algae in French Polynesia on the Centre D'Oceanologie de Marseille website: a brief but rather technical introduction to seaweeds with lots of photos, and detailed explanation of seaweed reproduction.
Hawaiian Reef Algae on the University of Hawai`i at Manoa website: a quick but rather technical introduction to seaweeds with study-guide lists of features; keys to identification; lots of photos.
How much is Too Much of a Good Thing? on the Florida Keys National Marine Sanctuary website: about microscopic algae and their role in the habitat.

Other references

Calumpong, H. P. & Menez, E. G., 1997. Field Guide to the Common Mangroves, Seagrasses and Algae of the Philippines. Bookmark, Inc., the Philippines. 197 pp.
Tan, Leo W. H. & Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp. online version
Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times of Labrador Beach. Division of Biology, School of Science, Nanyang Technological University & Department of Zoology, the National University of Singapore. 160 pp.
Ong, Jin Eong & Gong, Wooi Khoon (eds.), 2001. The Encyclopedia of Malaysia (Vol. 6): The Seas. Didier Millet, Malaysia. 144 pp.

a companion website to the chek jawa guidebook website©ria tan 2003 www.wildsingapore.com

a companion website to the chek jawa guidebook
website©ria tan 2003 www.wildsingapore.com