Introduced Marine Species

The Asian green mussel, Perna viridis, in Australia

Photo: Graham Wharton, Tropical Reef Shipyard.

In July 2001, Asian green mussels Perna viridis were found on the hull of a vessel in Cairns harbour in north Queensland. These mussels are not native to Australia. The discovery caused concern because in other parts of the world, Asian green mussels have become a pest. They can grow quickly and cover underwater walls, pylons, boat hulls and intake pipes. In some places, Asian green mussels form carpets 60cm thick and reach densities of more than 35,000 mussels per square metre. If Asian green mussels were to establish in Cairns harbour, the commercial value of the Port may be detrimentally affected and the mussels may compete with native mussels and oysters.

Perna viridis are commonly called Asian green mussels, green mussels or brown mussels. In this document, they are referred to as Asian green mussels.

DISTRIBUTION OF THE ASIAN GREEN MUSSEL
The Asian green mussel is a native of the tropics, from the northwest Indian Ocean and western Pacific Ocean. It is found from the Persian Gulf to the Philippines and from the east China Sea in the north to Indonesia in the south. It is an important aquaculture species, particularly in China, India, Thailand, Singapore, Indonesia and the Philippines. It has also been introduced for culture in many south Pacific islands, such as Fiji and eastern Polynesia.

The Asian green mussel has been accidentally introduced to Trinidad in the Caribbean, and then spread (probably by currents and human activities) to the coast of nearby Venezuela. In 1999, it was found clogging the intake canals of power plants on the Florida coast. It is expected that the mussels will spread south in water currents along the American coastline to the Florida Keys.

BIOLOGY OF THE ASIAN GREEN MUSSEL
The Asian green mussel has a bright green shell when it is younger which becomes darker green to brown as it gets older. The inside of the shell is iridescent white.

Photo: Dave Field, DWAP

Asian green mussels live for about three years and usually grow to about 8 cm long although they can reach 16 cm long. They feed on tiny plants and animals filtered from the water. Asian green mussels grow in warm waters from 26-32°C but can survive for a short time in water as cool as 10 C and as hot as 35°C. They grow in estuarine waters where the salinity is between 24 - 33 ppt but can survive in less salty water (down to 16 ppt). The mussel grows near the low tide mark but has been found as deep as 42 m.

The mussels can breed throughout the year. When they are ripe, the flesh of the male mussel is creamy white and that of the female is orange. The Asian green mussels are often stimulated to breed when the salinity drops, for example, after heavy rains during the wet season. They can also be stimulated to spawn when they detect sperm or eggs from other Asian green mussels in the water.

Male and female Asian green mussels release sperm and eggs into the water column when the water is about 21°C although spawning can take place in water cooler than 28°C. The fertilised eggs develop into tiny swimming larvae that spend 10-21 days washed about in water currents before settling on to a hard surface. The young mussels attach with strong byssal threads and then grow quickly; in some environments they can grow at about 1 cm per month. In some aquaculture environments, the Asian green mussels can begin to breed when they are about 2 cms long.

CONTROLLING ASIAN GREEN MUSSELS IN CAIRNS HARBOUR
In December 2001, a baseline survey in Cairns Port commissioned by the Environmental Protection Agency (EPA) was conducted by scientists from the CRC Reef Research Centre and the Northern Fisheries Centre at the Queensland Department of Primary Industries and Fisheries to determine the prevalence of Asian green mussels in the harbour.

This survey found Asian green mussels that were in low numbers and concentrated in a few areas. The EPA, with the assistance of CRC Reef Research Centre, the Queensland Department of Primary Industries and Fisheries, Queensland Transport, the Department of Defence, and the Cairns Port Authority commenced an emergency operation in Trinity Inlet on 19 March 2002. The operation involves inspection and decontamination of potentially infected vessels and dive surveys of Trinity Inlet to establish the extent of the Asian green mussel infestation. For more information on the Asian green mussel operation, visit the EPA website.

These areas have been targeted for further work, including the slipping of vessels and additional dive surveys, to attempt to define the extent of the infestation of the mussels. In addition, the entire port is being closely monitored for the settlement of new young mussels.

PREVENTING THE SPREAD OF ASIAN GREEN MUSSELS
The Environmental Protection Agency (EPA) has released a brochure that lists key steps to prevent the spread of Asian green mussels. Some of the steps are listed below. The entire brochure (The Tussle with the Asian Green Mussel) can be accessed via the EPA website.

The key to preventing green mussels hitching a ride on vessels is good maintenance and effective antifouling. Some practices recommended by the EPA are:

• Paint hulls with an appropriate antifouling in accordance with manufacturer's directions.
• Flush seawater inlets regularly with fresh water to kill newly settled pests.
• Regularly clean propellers and other underwater fittings that cannot be painted with antifouling paint.
• Remove any established green mussels when discovered. Note that in-water cleaning is banned in Australia under the ANZECC Code of Practice for Antifouling and In-Water Hull Cleaning.
• Ensure your boat hull is clean before traveling to other areas so that the mussels are not spread to other harbours and other vessels.
• Notify the Environmental Protection Agency (EPA) if you think you may have found green mussels - or any other potential pest species - so their spread can be monitored.

For more information:
CRC Reef Research Centre
PO Box 772 Townsville 4810 Qld
Ph: 07 4729 8400
Email: info@crcreef.com
Website: www.reef.crc.org.au

Environmental Protection Agency
EPA Building, 80 Meiers Rd, Indooroopilly Qld 4068
Ph: 07 3896 9250
Website: www.env.qld.gov.au

Northern Fisheries Centre
Dept Primary Industries
PO Box 5396, Cairns Qld 4870
Ph: 07 4035 0100

For a fact sheet about Asian green mussels:
CSIRO Centre for Research on Introduced Marine Pests (CRIMP)

For more information about marine pests and antifouling:
Environment Australia
CSIRO Centre for Research on Introduced Marine Pests (CRIMP)
Defence Science and Technology Organisation (DSTO)

To report possible sightings of green mussels contact:
Environmental Protection Agency
EPA Building, 80 Meiers Rd, Indooroopilly Qld 4068
Ph: 07 3896 9250
Website: www.env.qld.gov.au