Article | Updated 9 months ago
Green, brown, and red algae are organisms that look like plants. They possess modified ‘roots’, which act as holdfasts allowing the algae to attach to hard surfaces and avoid being swept away by ocean currents. These organisms require light to photosynthesise, just like true plants. Worldwide, there are over 7 000 species of algae.
The flowering plants or angiosperms (Phylum: Magnoliophyta) include the land dwelling plants. However, a few groups are adapted to live underwater or along the shoreline of the coast. Two such groups are the seagrasses and the mangroves.
Algae and plants have an important role in the underwater environment. They provide a source of food and shelter for a range of marine animals. Algae and seagrass beds provide ‘nursery’ grounds for many fish species. These beds give the young fish a place to hide from predators.
Green algae (Phylum: Chlorophyta) can range from single celled microscopic species to larger, plant-like forms, commonly referred to as seaweeds.
Like true-plants, green algae rely on sunlight for photosynthesis and this dependence will generally determine where they occur.
Green algae are an important part of marine food chains as they provide a food source for animals at the lower end of the food chain.
Some species of green algae are able to grow in moist areas on land. However, the majority can be found in aquatic environments.
Brown algae (Phylum: Phaeophyta), like red and green algae, can generally be distinguished by their colouration. Brown algae are commonly seen growing on coral reefs and rocky shores.
The pigments in brown algae are more efficient at absorbing sunlight than green algae and, therefore, brown algae can be found in deeper waters. Brown algae are less efficient at absorbing sunlight than red algae.
Brown algae are the fastest growing plants and the longest and heaviest of all the seaweeds.
Brown algae are harvested by humans to extract a substance known as alginic acid. This acid is used in the manufacture of many products including toothpastes, soaps and ice cream.
Red algae (Phylum: Rhodophyta) are distinguished by their colouration, which ranges from red to purple. They appear in single celled and larger, multi-celled, plant-like forms.
Red algae are able to photosynthesise at greater depths than both green and brown algae and are, therefore, more abundant in deeper waters. Like the other groups, red algae provide food and shelter for a range of marine animals.
Certain species of red algae are used in some Asian countries, mainly Japan, as a source of food due to its high vitamin and protein content.
Although, seagrasses are very similar to the terrestrial plants, they have become adapted to live underwater. They can be found in many different habitats, including coral reefs and areas of soft sediment.
Seagrasses can reproduce by two methods. Like terrestrial flowering plants, seagrasses can produce flowers and seeds. These seeds are then dispersed by the ocean currents. Seagrasses also have root-like structures, known as rhizomes, which grow along the seabed and sprout new leaves.
As with the other flora in aquatic environments, seagrasses provide an ideal habitat for a wide range of fauna. Approximately 60 species of seagrass are known to occur worldwide.
Mangroves are a specialised group of plants that are able to survive in waterlogged mud, which typically has a high level of salt. They have adaptations that aid in their survival in these harsh conditions.
These features include the ability to reduce the uptake of salt or to excrete salt through their leaves. Some species also possess special structures called pneumatophores, which allow oxygen to reach the roots of the plant.
Mangroves form important habitats along muddy shorelines in the Dampier Archipelago. The network of roots reduces the erosion of the shores through binding the sediment together and reducing water flow. The roots also provide a suitable habitat for fish and other animals, giving them a place to evade large predators.
Mangrove leaves that have dropped into the water and have begun decaying provide a source of food for other marine organisms.