Algal Reefs

About Algae



Green, brown and red seaweeds go under the scientific name of algae. The term 'seaweed' is misleading and does not do justice to these vitally important components of marine communities. They provide gases, nutrients, shelter and food and come in a wonderful array of colours and shapes. The algal communities around south-east Australia are very diverse, from encrusting forms that spread over rocks like a mat, to canopy-forming giant kelps that create forest homes for fish, rock lobsters, urchins and sea stars. There are hundreds of algal species in Victorian waters - creating some of the richest algal beds in the world.

Algal Health

Given the vast number of species and forms of algae it is difficult to summarise what constitutes a healthy bed of algae. In general, a change in the kinds of algae that you find in the site, a change in the condition of algae at a site, or the disappearance of a previously abundant species, may be indications of a decline in surrounding environmental conditions. Threats include pollution discharges from pipes, stormwater drains, rivers and creeks, fishing, collection and introduced species. Over the last few years, Giant kelp forests (Macrocystis) have been significantly reduced or have completely disappeared from areas round Tasmania and Victoria, possibly in response to global warming.

Natural processes such as storms can also destroy kelp beds. In many areas, the ecological balance has been further upset by an increase in the number of urchins through over-fishing of their natural predator, the rock lobster. In the northern part of Victoria, around Mallacoota, grazing urchins remove algae from the rock and create urchin 'barrens'. The introduced marine weed, Undaria pinnatifida, is a threat to native species in some areas as it competes with them for space and nutrients. Loss of habitat-forming species, such as large algae, may have a serious effect on other species.

Algal Anecdotes

The three groups of algae Green (Chlorophyta), Red (Rhodophyta) and Brown (Phaeophyta) can generally be can be identified by their colour however there are some exceptions.

Strictly speaking seaweeds have no flowers, leaves, roots, nor stems. A holdfast at the base attaches the algae to the seafloor and the remainder of the body, the thallus is divided into a thickened "stipe" (stem) and flattened "fronds" (leaves).

Kelps are a particular type of brown algae (order Laminariales) that have cylindrical stems and large leafy fronds. Giant kelp (Macrocystis pyrifera) is the largest seaweed in the world, growing up to 65 m long at a rate of up to 50 cm a day.

Alginate is a substance naturally produced by seaweeds. Brown algae such as giant kelp and bull kelp are commercially harvested for their alginate which is used as a stabiliser, thickener, emulsifier, and gelling agent in many products from toothpaste, icecream and salad dressing, to medical dressings, laboratory cultures, printing and cosmetics.

Not only do kelp forests and seaweed beds provide habitats for adult animals, these areas are also important for early life history stages when free-floating larvae move down towards the seafloor to change into their adult forms. Cray weed (Phyllospora comosa) gets its name from observations of small juvenile rock lobsters clinging to its fronds.

Where Can You See Reefs of Algae?

West Coast: Roger's Rocks, Killarney, Griffith Island, Lady Bay.

Central Coast: Pope's Eye (Harold Holt Marine Reserve), Lonsdale Wall and Nepean Wall. These areas in southern Port Phillip Bay support stands of Common Kelp (Eklonia) and Giant Kelp (Macrocystis). Thick Bull Kelp (Durvillaea) can be seen fringing the rock pools and upper tidal zone of Sorrento back beach.

East Coast: Bunurong marine park (Cape Paterson), Wilsons Promontory, Cape Everard