Pest species

There was a time when the marine environment was considered an inexhaustible resource. However, our research shows, and Victorians understand, that this is not true, but that our bays, coasts and seas are fragile and threatened, and need protection.

Many threats to our marine environment lie below the water's surface and are not visible to most people. Although out of sight, the introduction and establishment of marine pests below the sea surface is one such threat.

Introduced pests threaten the biodiversity and ecological integrity of Victoria's aquatic ecosystems, human activities such as aquaculture, and recreational and commercial fishing. These non-native species come in all shapes and sizes – from microscopic algae to seastars to large marine plants.

There are many introduced pests in Victoria's fresh and marine waters that have caused serious problems, including the North Pacific sea star, carp and willow. When introduced, these pests can dominate ecosystems and exclude native animals.

Freshwater pests species

Increased invasion of non-indigenous (not locally native) flora and fauna such as willows, Alligator Weed and carp are an established concern in freshwater systems throughout Victoria. Introduced fish significantly impact on native fish through predation, and competition for food and habitat.

Carp, for example, have become the dominant freshwater fish in many fish communities in south-eastern Australia. In addition to displacing native fish, they increase water turbidity and damage aquatic plants.

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Marine pest species

The introduction of pest species is potentially a great threat to the marine environment. Exotic species have been travelling from port to port since humans have been travelling the oceans of the world. Most do not create a big problem in a new environment. However some become pest species and can have great ecological and economic impact.

The international community is moving to address this issue, with Australia taking the lead. However, achieving international and national consensus will take some time.

How species invade

Many marine pests have been introduced into Victoria via shipping involved in globaland interstate trade and boating activities. Vessels entering Victorian ports are potential sources of marine pests. Already our natural ecological balance is threatened by exotic species in a variety of ways, such as competition for food.

Ballast water

Vessels need ballast to operate safely at sea. Ballast water is taken up or discharged when cargo is unloaded or loaded, or when ships need extra stability in response to foul weather. However, ships also pick up the plants and animals that live in the sea water. Discharge of ballast water releases these into new areas and they can become marine pests. There are programs for ballast water management.

Vessel fouling

Many exotic species can attach to the hulls of vessels and in port they may release eggs, spores and larvae which can settle on nearby berths and piers. Other organisms hide in pipes and other apertures and can be transferred as adults from one place to another.

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Ten marine pests

Some 99 exotic marine organisms are known to have become established in Victoria. Ten of these are of particular concern to Victoria as they may be harmful to our environment.


Broccoli weed	Japanese kelp	Northern Pacific seastar

Common name	Scientific name
Northern Pacific seastar	Asterias amurensis
European shore crab	Carcinus maenas
Broccoli weed	Codium fragile tomentasoides
European clam	Corbula gibba
Asian mussel	Musculista senhousia
Fanworm	Sabella spallanzanii
Japanese kelp	Undaria pinnatifida
Three toxic dinoflagellate species dinoflagellates (Alexandrium sp. and Gymnodimium sp.)

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More information

The Victorian Government has introduced domestic ballast water management arrangements for Victoria that entered into force on 1 July 2004.

The Action Statement Introduction of Exotic Organisms into Victorian Marine Waters and the Interim Victorian Protocol for Managing Exotic Marine Organism Incursions are available from:

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