Red, green and brown, Algae are essential!
Algae are a diverse group of simple, plant-like organisms found in aquatic environments. They play an important role, forming the base of the food chain for marine life. They range from tiny, single-celled organisms called phytoplankton, visible only with the aid of a microscope, to the large kelps that can form massive undersea forests.
Distribution
Algae have a wide distribution across various habitats. Alage can be found in oceans, freshwater bodies, and even on land.
Plant … or not?
In the aquatic environment, the term ‘plants’ is sometimes used in a very flexible sense, and can refer to seagrasses, algae, and photosynthetic bacteria.
Algae lack the features of true flowering plants such as roots, stems, and leaves. Instead of roots, they anchor themselves to rocks or other organisms using root-like attachments called holdfasts.
Algae contain chlorophyll and other photosynthetic pigments, which are used to create oxygen. They form the basis of the food chain in the marine environment, converting energy from sunlight into starches and sugars in a process called photosynthesis.
The term algae encompasses several groups that are only distantly related to one another, these include the red algae, geen algae, and brown algae.
Algae include a diverse range of microscopic (microalgae) and macroscopic (macroalgae) forms.
red algae
Microalgae
Microalgae, also known as phytoplankton, can only be seen through a microscope, and are typically found in rivers, estuaries, and oceans.
The two main classes of phytoplankton are dinoflagellates and diatoms. They are single-celled species which can exist individually, or in chains or groups. Depending on the species, their sizes can range from a few micrometres to a few hundred micrometres.
Because they can photosynthesise, microalgae are very important for life on Earth. It is estimated they produce between 50 and 75 per cent of the Earth’s oxygen and simultaneously absorb about 25 per cent of the greenhouse gas – carbon dioxide.
Macroalgae
Macroalgae are multicellular and visible to the naked eye. They can vary in size, ranging from a few centimetres to many metres long. The piles of seaweed often washed up onto beaches are a mixture of macroalgae and seagrass and are referred to as ‘sea wrack’.
Macroalgae grow in a wonderful variety of forms including large leafy types like sea lettuce, filaments, clumps, and balls.
They are divided into 3 colour groups – green, brown and red. They are not always true to their colour, as sometimes different pigments can dominate and mask their actual colour, making identification difficult.
Macroalgae form vital habitats for a wide array of marine life.
anatomical diagram of macroalgae
Weeds of the ocean
Macroalgae are often called ‘seaweeds’, but this is really a misnomer as normally they are a natural component of the marine ecosystem and not weeds at all.
Algal blooms
An algal bloom is caused by a rapid increase in the population of microalgae in an aquatic system.
Some blooms are caused by high levels of nutrients (particularly phosphorus and nitrogen) in waters. These nutrients enter the waterways mainly as a result of activities on nearby land. As concentrations of these nutrients in water increase, they may accelerate the growth of algae and green plants.
While most algae blooms are a natural part of aquatic ecosystems and are not harmful, some can cause serious problems, such as producing toxins and impacting water quality. These are known as harmful algal blooms (HABs).
Algal blooms are not a recent phenomenon – Captain Cook recorded an algal bloom during his voyage in 1770.
Alexandrium algal bloom, photo: Department of Biodiversity, Conservation and Attractions
Green algae (Phylum: Chlorophyta)
Green algae can be found in most habitats, from marine to freshwater to terrestrial.
Their colour is usually grass-green or a slightly greyish hue of the same colour. They may be either attached or free-floating microscopic (planktonic) algae.
Marine-attached green algae are commonly found on shallow rocky shorelines where the sunlight penetrates the water easily so they can photosynthesise.
Green algae come in a variety of shapes including flat sheets, cylinders, strings of beads and spheres of hair-like filaments.
It is thought that all terrestrial plants evolved from green algae, mainly due to the presence of chlorophylls a and b, which give them their green colouration.
sea lettuce, a green algae abundant near shallow shores
Brown algae (Class: Phaeophyceae)
Brown algae are found living mainly on rocks, seagrasses or other seaweeds. They are the heaviest and largest of seaweeds and are frequently seen on shorelines and in shallow water.
Almost entirely restricted to the marine environment, they are generally shades of brown, though some species can appear blue underwater.
Large brown algae such as Kelp forests, can grow up to 35m long. In Western Australia, kelp does not reach the same lengths with some species reaching up to 1.5m. They thrive in shallow, cool waters where they can attach to rocky reefs.
brown algae kelp forest near Rottnest Island
Red algae (Phylum: Rhodophyta)
Red algae are the most numerous of the three seaweed groups outnumbering the brown algae and the green algae 3:1 in Australian waters.
Red algae are generally the most abundant algae in deep water as they can photosynthesise in lower light conditions. They are relatively small to medium in size and never form extensive beds.
Recognising red algae can be difficult as some appear anything but red. Some hints include any trace of red colouration. They come in a variety of forms and their texture may vary from fine and delicate to hard and crusty.
‘Red tides’ (brownish-red discolouration of marine waters) are caused by a type of phytoplankton, not red algae.
red algae
Tiny but mighty
Microalgae is a major component of plankton – those minute organisms that float, swim weakly or drift in the water and are the first link of aquatic food chains. They provide the main food source for many species, including filter feeders such as oysters and mussels, and zooplankton including crustaceans.
Macroalgae are habitats for small animals such as molluscs and shrimps and nursery areas for juvenile fish, crabs, and prawns. They also shelter fish and crustaceans from predators such as larger fish or birds and can help to reduce erosion along the shoreline.
juvenile mullet feeding on algae
Invasive species
Invasive species are introduced into environments where they do not live naturally. They can spread a number of ways; including through ships discharged ballast water, bio-foul on boat or ship hulls, aquarium imports, even marine debris.
A variety of marine algae have been introduced to Western Australian waters, some of which are considered invasive and pose potential threats to the environment where they outcompete native species and alter habitats. Some invasive algae can accumulate toxins and affect seafood safety.
For more information on invasive algae and to stay up to date with biosecurity alerts, refer to Aquatic pests, weeds and diseases on our website www.dpird.wa.gov.au.
Humans and algae
Algae are essential for the wellbeing of the coastal ecosystem, but they are also of huge value to people. Some four hundred different species of seaweeds around the world are used by people for food, stock feed, aquariums, medicines, cosmetics, and fertilizers.
More recently algae have been used to produce algal biodiesel. This product has the potential to be a sustainable, environmentally friendly alternative to diesel.
Bibliography
Commonwealth Scientific and Industrial Research Organisation:
www.csiro.au
Department of Biodiversity, Conservation and Attractions, Western Australia:
www.dbca.wa.gov.au
Department of Climate Change, Energy, the Environment and Water:
Department of Primary Industries and Regional Development, Western Australia:
www.dpird.wa.gov.au
Department of Water and Environmental Regulation, Western Australia:
www.wa.gov.au/organisation/department-of-water-and-environmental-regulation
Marine Education Society of Australasia:
www.mesa.edu.au
Bridgwood, S. 2010. Codium Fragile ssp. Fragile (Suringar) Hariot Summary Document. Department of Fisheries.
Hallegraeff, G.M. 2007. Algae of Australia. CSIRO and Australian Biological Resources.
Edgar, G.J. 2008, Australian marine life: the plants and animals of temperate waters, 2nd edition. New Holland Publishers: Sydney.
Huisman, J.M. 2000. Marine Plants of Australia. University of Western Australia.
Glossary
Algae
Aquatic plant-like organisms.
Algal bloom
Rapid and excessive growth of algae, caused by high nutrient levels and favourable conditions.
Chlorophyll
A green pigment found in photosynthetic organisms that is able to capture the sun’s energy.
Filter feeder
An animal that strains food such as plankton from water using a sieve-like structure in its mouth.
Macroalgae
Aquatic “plants” that form underwater and can be seen with the naked eye.
Microalgae
Microscopic algae that require the aid of a microscope to be seen.
Microscopic
Organisms that cannot be seen with the naked eye.
Photosynthesis
The process by which green plants and other organisms use sunlight to synthesise foods from carbon dioxide and water and release oxygen as a byproduct.
Photosynthetic
Relating to or involved in the process of photosynthesis.
Phytoplankton
Plankton consisting of microscopic plants.
Plankton
Microscopic organisms that drift in water.
Terrestrial
Living or growing on land; not aquatic.
Zooplankton
Plankton consisting of microscopic animals and larval stages of animals.