What is blue-green algae?
What causes a blue-green algae bloom?
How do blue-green algae blooms normally disappear?
Problems with blue-green algae
Managing blue-green algae blooms
Marine algae blooms
What is Trichodesmium?
How to spot a Trichodesmium bloom
Is Trichodesmium toxic?

What is blue-green algae?

Despite the name, ‘blue green algae’ refers to a phylum of bacteria called ‘cyanobacteria’. Numerous types (species) of this bacterium are naturally found within Australian fresh and marine waters, and play an important role in maintaining a healthy aquatic ecosystem.

Under certain conditions, cyanobacteria can rapidly grow and dominate the water, called an ‘algal bloom’.

These blooms can either be seen across the top of a waterway, or throughout the water column, depending on which type is causing the bloom.

 Signs of a bloom include:

• Green, soupy looking water
• Green ‘flecks’ throughout the water
• Surface scums, mats or films
• Swampy or fishy smell.

Blue-green algae factsheet

What causes a blue-green algae bloom?

Like our own digestive systems, waterways rely on a balance of ‘good’ and ‘bad’ bacteria to function normally.

Under favourable conditions or following a rapid change in a waterway’s chemistry, the balance of bacteria within a waterway can become unstable; and cyanobacteria may rapidly multiply, causing an ‘algal bloom’.

Traits of a waterway that may trigger a bloom include:

• Warm water temperatures; smaller bodies of water can warm up faster
• Increased nutrient levels; decaying plant matter (e.g. after a storm) or run-off fertilisers from gardens
• Low levels of ‘healthy bacteria’; cyanobacteria compete with ‘healthy’ bacteria for nutrients, so a good balance of healthy bacteria will hinder the cyanobacteria from blooming,
• High sunlight; many blooms form as we enter Spring/Summer,
• Stagnant water; calm or still water is easier for the bacteria to multiply within and dominate, and
• Drought conditions.

Some Australian waterways host algae blooms annually, as part of their natural cycle. For example, waterways which naturally deplete during the dry season, often have blooms at the start and end of wet season.

How do blue-green algae blooms normally disappear?

Most blue green algae blooms are natural events, and the bloom will disappear as the waterway returns to its natural balanced state. This process begins as the cyanobacteria starts to deplete what nutrients it can feed from; and the bloom will die-off as a result.

Problems with blue-green algae

• Blue-green algae is easily moved by wind and water currents. As a result, blooms may accumulate into thick mats where these currents are moving toward.
• Some species of blue-green algae release toxins as they breakdown, which are a potential health risk to humans, pets, livestock, and in major circumstances, aquatic wildlife.
• If an algal bloom ‘dies-off’ rapidly, it can deplete the oxygen levels within the waterway
• Algae blooms can also discolour the water and create an unsightly and foul-smelling scum on the surface.

Managing blue-green algae blooms

Most blue-green algae blooms are natural events that cannot be stopped; however, steps can be taken to reduce the frequency and severity of these blooms.

Some of the actions that Council undertakes to minimise blooms, include:

• Using equipment to keep water moving (such as fountains) in waterways known for blooms
• Regulated use of fertilisers in our gardens and greenspaces, to minimise fertiliser run-off to waterways
• Water monitoring of relevant waterways during seasonal periods that may trigger blooms.

Marine algae blooms

Some species of blue green algae naturally occur in saltwater, particularly in warmer tropical and subtropical ocean waters. While marine blue green algae are less frequently seen compared to their freshwater counterparts, certain environmental conditions can cause blooms to form on beaches and within coastal creeks.

Such ocean conditions include:

• Calm waters
• Northerly currents
• Warm water temperatures
• Excess nutrients entering the ocean (e.g. following floods).

What is Trichodesmium?

The main species of marine blue green algae seen in the Gladstone Region, is ‘Trichodesmium’ (try-koe-DES-me-um). Trichodesmium blooms are occasionally misidentified or are called misleading nicknames, including coral spawn, sea sawdust, whale sperm, whale food and sea scum.

Trichodesmium blooms are most noticeable when they approach or wash up upon shore.

These blooms, beached or free floating, usually disappear in a few days.

In rare circumstances, large storms and/or king tides may cause Trichodesmium to enter brackish coastal creeks, where the bloom may persist longer than average due to the stagnant/slow moving waters.

How to spot a Trichodesmium bloom

Trichodesmium blooms are common between August - December when increased temperatures, sunlight and other environmental factors are favourable to growth. A Trichodesmium bloom can be identified by:

• A characteristic rusty-brown colour, turning yellow-green as the bloom decays
• Tiny flecks of ‘sawdust’ in the water,
• Clumps of red-brown scum floating on or near the water’s surface.
• A putrid, almost ‘fishy’ odour.

Is Trichodesmium toxic?

In most circumstances a Trichodesmium bloom is harmless; however during the decay process it may decrease oxygen levels of the water which may impact aquatic animal health.

Where Trichodesmium becomes stagnant, a transparent toxin may be released. This release is indicated by the colour of the bloom, as it changes from a rusty brown colour, to a green/pink colour.

This toxin is rarely in a high enough concentration to pose a threat to human health. Trichodesmium can be easily washed off the skin by rinsing with water. As a precaution, Council advises beach users to avoid swimming within or contacting waters containing an active Trichodesmium bloom.