Northern Pacific Seastar
- Why are Northern Pacific Seastars considered pests?
- How to distinguish the Northern Pacific Seastar from native seastars
- Where are Northern Pacific Seastars native?
- How did they get to Australia and where are they found?
- What is being done about the Northern Pacific Seastar in Port Phillip Bay?
- Report a marine pest
Why are Northern Pacific seastars considered pests?The Northern Pacific Seastar is considered a serious pest in Australia because of its impact on native marine ecosystems and marine industries such as shellfish farming.
Impacts on native species
Northern Pacific Seastars are known to have detrimental effects on native marine organisms, mainly because they are voracious predators that eat a wide range of native animals. They can have a major impact on populations of native shellfish, which are important components of the marine food chain. In Tasmania's Derwent estuary for example, they have become the dominant invertebrate predator.
The seastars have also been directly implicated in the decline of the endangered spotted handfish (Brachionichthys hirsutus) in Tasmania. It is suspected that the seastars prey on handfish egg masses, and/or on the sea squirts (ascidians) that handfish use to spawn on.
Impacts on marine industries
The threats posed by the Northern Pacific Seastar to commercial shellfish farming (mariculture) are well documented. Outbreaks in Japan cost the shellfish mariculture industry millions of dollars annually in the form of control measures and losses due to predation. The seastar has also been reported to affect oyster production on some marine farms in south-eastern Tasmania.
The Northern Pacific Seastar has the potential to rapidly establish large populations in new areas. For example, recent estimates indicate the population had reached 12 million two years after they were first detected in Port Phillip Bay. Tens of thousands of seastars have been removed in eradication attempts, but with little effect on overall population numbers. Even in Japan where the seastars are native, some populations show 'boom and bust' cycles, reaching plague proportions for two to three years followed by rapid declines.
How to distinguish the Northern Pacific Seastar from native seastarsUnfortunately a number of our native species are suffering from mistaken identity and being removed from the water. These include the 11-leg seastar and the rare native five-armed seastars that have rounded rather then pointed tips at the end of each arm.
Native seastars should not be harmed, and some of them are known to eat the Northern Pacific Seastar. It is important that you know how to identify the native species from the pests before you remove any seastars from the water.
For further information see Northern Pacific Seastar fact sheet
Where are Northern Pacific Seastars native?
Throughout their natural range, the Northern Pacific Seastar prefers temperatures between 7 and 10ºC, but has adapted to warmer waters (up to 22ºC) in Australia and other countries. The seastars prefer mud, sand or rocky habitats in sheltered areas of the intertidal zone down to depths of around 25 metres, and occasionally to 200 metres. They are not normally seen on reefs or in areas of high wave action.
Reproduction and dispersal
Juvenile seastars grow rapidly, reaching sexual maturity when approximately 10 cm in diameter and around one year old. In south-eastern Australian waters, spawning occurs during winter when water temperatures are around 10 to 12ºC. Females are capable of producing up to 20 million eggs each. After fertilisation the eggs develop into free-swimming larvae, remaining in the plankton for up to 90 days before settling and changing into juvenile seastars. This long planktonic stage increases their capacity to disperse over a wide area.
Northern Pacific seastars are also capable of growing a full body from a single leg, as long as a small portion of the central disc remains. Individuals live for up to five years.
Northern Pacific Seastars are voracious predators and will eat almost any animal they can capture. In Australian waters they have been recorded feeding on a variety of native animals including shellfish (bivalve and gastropod molluscs, barnacles, crabs and other crustaceans), worms, sea urchins and other seastars (echinoderms) and sea squirts (ascidians), although they seem to have a strong preference for shellfish. Once alternative food sources have been exhausted they can become cannibalistic. They can detect food from some distance away and will dig shallow pits to extract buried prey.
How did they get to Australia and where are they found?
The Northern Pacific Seastar is established at two Australian locations: Tasmania's Derwent River Estuary and east coast and Victoria's Port Phillip Bay.
The Northern Pacific Seastar was probably introduced into Australia through ballast water from Japan. Although it was first confirmed in the Derwent River in Tasmania in 1992 it is believed to have been introduced earlier than this date. In Tasmania the highest population densities are found in the Derwent estuary, but they are also found on the east-coast of Tasmania down to Southport in the south.
The Port Philip Bay infestation is likely to have been introduced from the Derwent River by ship ballast water. It was first confirmed in Victoria in August 1995 when the first adult Northern Pacific Seastar was caught off Point Cook. Despite a major effort to find and eradicate the seastar, only three more adults were found in the next 30 months - one in September 1995, one in August 1996 and another in April 1997.
In 1998, there was evidence that the seastar was breeding in Port Phillip Bay with four juveniles found off Dromana. By the end of April 1998 over 100 juveniles had been caught in the same area. In February 1999 the seastar covered a 100 square kilometre area in the eastern and central part of Port Phillip Bay.
Efforts were stepped up to reduce the chance that human activities would lead to this pest's introduction to other areas of Victoria through the movement of ballast water, aquaculture equipment and small vessels. These efforts were backed by projects to help understand scientifically how to best deal with the Northern Pacific Seastar in the long term.
In early 2004 individual Northern Pacific Seastars were found on a beach near Inverloch, a coastal town facing Bass Strait and 143kms south-east of Melbourne. If allowed to establish, it was likely that the seastars would spread along the Victorian coastline and up into New South Wales in future years with the water currents. A concerted effort to find and eradicate this outbreak before they were able to breed in the area was mounted. Surveys in 2008 suggest that this eradication effort has been successful. Read the case study on why eradication was attempted on this population.
What is being done about the Northern Pacific Seastar in Port Phillip Bay?
Although an eradication effort was attempted when the Northern Pacific Seastar was first found in Port Phillip Bay, these efforts were unsuccessful. Because the seastars are highly productive (with each female releasing up to 20 million eggs each),100 percent of the population must be removed for an eradication attempt to be effective. Should just a few individuals be left the population will successfully breed.
The Northern Pacific Seastar is now established in Port Phillip Bay. The seastars are present as adults and larvae in Port Phillip Bay waters at various times of the year.
Current technology is unable to eradicate this species from the Bay without causing severe side effects to the environment. Therefore the current priority is to stop this marine pest from spreading to new areas along Victoria's coastline.
Report a marine pestIf you suspect you have seen a Northern Pacific Seastar outside of Port Phillip Bay, you should report it to the Customer Service Centre on 136 186. If possible, remove the pest and preserve it in a container of salt water or freeze it. The Customer Service Centre will provide instructions on what to do with the specimen. If collecting a specimen is not possible, a clear photograph can also be useful for identification
For information about identifying native seastars see Northern Pacific Seastar fact sheet (PDF - 347 KB)