Marine Life in Focus

Marine Life in Focus...giving you a snapshot of species found in Western Australia.

Seaweed

Though widely considered as simple marine plants, seaweeds are actually plant-like organisms called algae. They do not have true stems, leaves, flowers or fruits, or roots, instead anchoring themselves to rocks by root-like holdfasts. They form the basis of the food chain in the marine environment, using energy from sunlight to make food. Although seaweeds are divided into three colour groups (green, brown and red), they are not always true to the group, as classification is based on their life history and type of reproduction, rather than colour.

Green algae are characteristically green, although colour can range from yellowy-green to almost black. They exist as both large attached algae and free-floating microscopic (planktonic) algae, in both freshwater and marine environments. Marine attached green algae are commonly found on shallow rocky shorelines where the sunlight penetrates the water easily. It is thought that all terrestrial plants evolved from green algae, mainly due to the presence of chlorophylls a and b, which gives them the green colouration.

Brown algae contain most of the large conspicuous algae seen on rocky shorelines and in shallow waters. Brown algae are the heaviest and largest seaweeds, and the fastest growing of all the algae. Almost wholly restricted to the marine environment, they are generally shades of brown, except for some that can appear blue underwater. Nearly all species of brown algae remain fastened on rocky or other firm habitats by a holdfast, although some species are free-floating.

Red algae are the most numerous of the three seaweed groups but are relatively small and not easily seen, so are not noticed as often as green and brown algae. Red algae are generally the most abundant algae in deep water as they can tolerate lower light conditions than their relatives. Red algae come in a variety of forms and their texture may vary from fine and delicate to hard and crusty.

Did you know?
Some types of seaweed:

• are used as a food sources in many countries in salads, soups and other dishes.
• contain a gelatinous substance called algin that is widely used as a thickening or stabilising agent in products such as ice cream, salad dressing, pet food and toothpaste.

 

Ulva, or sea lettuce as it is more commonly known, is named for its appearance and the fact it is edible.