Introduced marine organisms in Port Phillip Bay

How are marine organisms spread?

Most species of marine organisms do not occur throughout the world, but are restricted to a particular region. However, marine scientists now know that many marine animals, as well as seaweeds and other algae, are being accidentally spread worldwide, by humans. There seem to be three common ways that this occurs:

Ballast water. Ballast tanks of ships are filled with seawater to balance the cargo load. These tanks may spread marine organisms, often as tiny larval stages that are pumped in along with the ballast water.

Fouling organisms. Organisms that can attach to a ship’s hull can easily hitch-hike and thus become established in a new location.

Accidental associates. Oysters and other shellfish that are moved to establish fisheries in new locations have other organisms living among their shells. Many small species have undoubtedly been spread in this way.

Regulations are now being put in place to try to minimise spread of marine life, but many foreign organisms are already well established and spreading further in Australian seas. The long-term impacts and effects on native marine life are not yet known.

Introduced organisms in Port Phillip Bay

At least 100 marine organisms have become established in Port Phillip Bay, mostly as a result of shipping traffic through the Port of Melbourne. These include crabs, sponges, algae, worms, molluscs, sea stars and fish. Seven of the most prominent introduced species in Port Phillip Bay are:

Northern Pacific Seastar Asterias amuensis — This large sea star has five arms with pointed tips and is mottled yellow and purple in colour. It is native to the northeastern Pacific, around Japan, Korea, Russia and China. The Northern Pacific Seastar was discovered in Tasmania in 1986 and in Port Phillip Bay in 1995. In the Derwent estuary near Hobart it now dominates the sea floor. In Port Phillip Bay it is now widespread.  In January 2004 the Northern Pacific Seastar was found to have spread to shallow reefs near Inverloch in southeastern Victoria.  Volunteer divers and staff of the Department of Sustainability and Environment are attempting to eradictate this latest outbreak.

Northern Pacific Seastar
Source: Museum Victoria

Japanese Kelp Undaria pinnatifida — This seaweed of the northern Pacific was first recorded in Tasmanian waters in 1988, and in Port Phillip Bay in 1996. It has also been introduced to New Zealand, Europe and Argentina. Japanese Kelp spreads quickly, colonising bare surfaces, and often replaces native seaweeds. It is the only kelp in southern Australia that has a single blade with a distinct midrib arising from each holdfast. The much more widespread native kelp Ecklonia radiata is similar but lacks the midrib.

European Shore Crab
Photographer: Michael Marmach / Source: Museum Victoria

European Shore Crab Carcinus maenas — This dark green crab has five notches on each edge of the carapace (shell) outside the eyes. It was first recorded in Port Phillip Bay in 1900 and now occurs widely in southeastern Australia. It has also been introduced into many other regions of the world. The European Shore Crab is known to exclude native crabs from its immediate habitat.

European Fan-worm Sabella spallanzanii — This fanworm (sometimes referred to as Spirographis spallanzanii) lives in tubes attached to hard objects and forms dense clumps that may be more than 30 cm high. Its fan forms a distinct spiral when opened. It was first recorded in Port Phillip Bay in the mid-1980s and is now common, attached to pier piles in many locations. The European Fan-worm is native to the Mediterranean Sea but is also introduced in Java and Brazil. A native fan worm, Sabellastarte australis (previously known as Sabellastarte indica), is similar in size but is solitary and its fan does not form a distinct spiral.

Three species of bivalve molluscs Musculista senhousia, Corbula gibba and Theora fragilis — These small bivalves are not readily seen by casual visitors to the coast, but during a recent survey Corbula gibba and Theora fragilis were found to be among the most common marine invertebrates on the sea floor of Port Phillip Bay. The mussel Musculista senhousia was discovered in Port Phillip Bay in 1982 and is now displacing a native mussel, Xenostrobus inconstans.

Visitor Information

Specimens of the molluscs Musculista senhousia, Corbula gibba, Theora fragilis, the crab Carcinus maenas and the sea star Asterias amuensis can be seen in the Discovery Centre at Melbourne Museum.

Further Reading

Edgar, GJ. 2000. Australian Marine Life. revised edition. Reed, Kew, Victoria.
[contains many images of native marine species, and of some introduced species also]

Hewitt, C. L., Campbell, M. L., Thresher, R. E. and Martin, R. B. 1999. Marine Biological Invasions in Port Phillip Bay, Victoria. Technical Report No. 20. CSIRO Centre for Research on Introduced Marine Pests.
[a technical reference on introduced marine species in Port Phillip Bay]

Comments (4)

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sarah 18 March, 2010 09:52
how where the european fan worm introduced into australia and why?
Bruce Webster 7 February, 2012 12:00
Whilst swimming at Parkdale beach, Victoria, on Saturday 4 Feb, I noticed hundreds of seagulls sitting just past the sandbank about 50 metres from shore. I went out to the area they occupied, and was surprised to see a red worm about 12cm long swim up from the bottom. Not long afterwards, I saw another but I couldn't catch it. I assume that the presence of these worms was the reason for the congregation of seagulls. Can you provide me with any information as to the species of these worms? Thank you, Bruce Webster.
Discovery Centre 8 February, 2012 12:39

Hi Bruce, the red worms that you saw at Parkdale are almost certainly breeding polychaete worms, in our part of the world these are likely to be either family Nereididae or Glyceridae (on coral reefs palola worms, family Eunicidae, also do this and are collected by Pacific Islander natives as food). Both those families are known to swarm en masse. The phenomenon is world-wide wherever these worms occur but it is reported often enough in Australia (often in fishing magazines since under these conditions it is easiest for fishermen to harvest these worms for bait, and also since fish (like the seagulls) gather to feed on the numerous polychaete worms. Often this occurs on a monthly cycle and during the night, on a full moon, so it is interesting that you observed it during the day. If you see it again our Curator has said he would be happy to see some of the worms to know which species is involved.

If you want more information on this phenomenon, try Wikipedia or other online sources and use the search term “epitoky”, which describes the body changes that take place in swarming breeding worms (typically the “feet” of the polychaetes become enlarged and more paddle-like, for better swimming).


barry 24 July, 2014 14:07
can you please name two vertebrates and two invertebrates that live in port Phillip bay or the Victorian coastal waters?
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Internet Resources

The Australian Government's National System for the Prevention and Management of Marine Pest Incursions site includes a link to the National Introduced Marine Pest Information System