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.