Where does the Northern Pacific Sea star live?

Answer 1

The Northern Pacific Seastar is a native species to the coasts of China, Korea, Russia and Japan, and they are also found across the Bering Sea in Alaska and northern Canada.

Habitat

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 meters, and occasionally to 200 meters. 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 fertilization 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 Platonic 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.

Diet

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 seastars, 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 kilometer 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.

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.