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Edition 15: Marine pests

In this edition:

Marine pests in our bays and waterways can adversely affect aquatic habitats, food chains, the ecosystem, and our enjoyment of the marine environment.

An example of how quickly marine pests can invade native marine environments in Victoria is the Northern Pacific Seastar (Asterias amurensis). This invasive species was first reported in Port Phillip Bay in 1995; populations established so successfully that five years later numbers in Port Phillip Bay were estimated to be well over 100 million individuals.

Marine pests in Victoria

Marine pests are highly invasive, non-native animals and plants that can cause significant harm to Victoria's marine environment. These pests can include a wide range of organisms, such as sea stars, seaweed, crabs, mussels, fish, sea squirts, amongst others.

Where marine pests come from

Marine pests can arrive in Victoria from other parts of the world or even other Australian waters. Many of them can arrive:

  • as unwanted tourists attached to the hulls of ships that visit our ports.
  • as larvae in ballast water.
  • accidentally through the aquarium trade

Learn more about how you can reduce the spread of marine pests.

Why marine pests are a problem

Once introduced, marine pests reproduce quickly, often producing large numbers of offspring that can rapidly spread to new areas.

They compete with native species by preying upon them, and outcompeting them for space, light, food, or overgrowing them.

They can also introduce diseases and parasites to our native species, and clog internal pipework resulting in overheating and damage to boat motors.

Because of their invasive nature, marine pests pose a significant threat to our marine native biodiversity and economy. Once marine pests become established, it is nearly impossible to eradicate them.

Established marine pests in Victoria

The following are high-risk marine pests that are known to be already established in parts of Victoria:

Northern Pacific Seastar (Asterias amurensis)

Image of a Northern Pacific Seastar

An invasive species of seastar currently present in Port Phillip Bay. It is characterised by having five arms with pointed upturned tips and being yellow/orange with purple markings. It can grow up to 50 cm across when fully mature. It is normally found in bays, estuaries, and reefs in habitats, such as seagrass, mussel beds, rock pools and rocky reefs, and artificial structures, such as marinas and ports.

During the cooler months, individuals aggregate to spawn, so numbers tend to be higher at a single location.

This is an aggressive predator of native and commercially important species including scallops, mussels, and oysters. Not only does it pose an ecological threat to biodiversity, but it also has an economic impact by affecting the aquaculture and fisheries industries.

Wakame (Undaria pinnatifida)

Image of Wakame

An invasive seaweed that is established in Port Phillip Bay, Apollo Bay harbour, Port Welshpool and Portland. Its main features are the presence of a frilly growth, known as sporophyll, at the base, a well-defined stipe that extends through the whole length of the blade as a mid-rib, and smooth, thin blades that finish before the base of the plant. The colour ranges from green to golden brown, with the stipe being lighter coloured.

This species is more commonly found during the cooler months, from low tide mark to 20 m in habitats such as rocky reefs, aquaculture equipment and hard surfaces, such as boats which accidentally transport It around the state. Wakame can rapidly take over areas previously devoid of large algal species.

Asian Shore Crab (Hemigrapsus sanguineus)

Image of an Asian Shore Crab

An invasive crab present in Port Phillip Bay. It can be identified by the banded patterns on its walking legs, the three spines on each side of the eyes and the spots on its claws. The shell can grow to up to 4cm wide and is characterised by having a squared shape and a colour that goes from green-purple to orange-brown.

It can be found in exposed rocky coasts, estuaries, and shallow waters, on a range of surfaces including shells, beneath rocks and artificial structures.

This species can outcompete native species and preys on crabs and shellfish, mainly oysters and mussels.

What can you do to help?

Although marine pests can spread naturally, they are normally transported around Victoria on the hulls of vessels or in areas and equipment that are not cleaned and dried properly.

Everyone can play a part in reducing the introduction and spread of marine pests and protecting Victoria’s marine environment. Some of the ways that you can help are:

  • Remembering to ‘Check, Clean, Dry’ boats and fishing, diving, snorkelling and surfing equipment that has been in the water.
  • Joining local volunteering groups with an interest in marine biosecurity
  • Keeping an eye out for unusual marine species and reporting suspected marine pest sightings to

Visit the Agriculture Victoria website and download a copy of Victoria’s Marine Pest Deck to learn more about high-risk established and exotic species that can affect Victoria’s unique marine environment and industries.

Front cover of the 'Marine Pest Deck' that also states 'Invasive Species Guide' and 'Protecting Victoria's marine environment from high-risk marine pests'

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Further Information

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