The seastar is a large predator, reaching sizes 40 to 50 cm in diameter. In its native range, the seastar prefers water temperatures between 7 and 10oC, but can also be found in warmer waters (up to 22oC) in Australia and other countries. It is fast growing and can produce up to 20 million eggs per adult female. It can live for up to five years. It generally is found close to shore on either mud, sand or pebble substrates but can live in depths up to 200 metres. It can grow to 50 cm wide (arm tip to arm tip).
Where did they come from?
It is native to the coasts of northern China, North Korea, South Korea, Russia and Japan.
Where are they found in Australia?
Its distributionis increasing, having been introduced into many countries, including Australia. It was first found in Tasmania in 1986 and by 1995 was also found in Victoria.,
How was it introduced?
Based on the distribution of northern Pacific seastar populations in shipping ports and routes, the most likely mechanism of introduction is the transport of free-swimming larvae in ballast water for ships. The ships suck in the ballast water containing seastar larvae in a port in Japan for example, and let it out in a port in Tasmania. The larvae come out with the water, and metamorphose into juvenile sea stars.
It has also been spread by the transport of commercial bivalve shellfish for aquaculture.
What is its impact?
The northern Pacific seastar is a very active predator eating almost any animal it can capture. It has a prefenrce for shellfish however. I prises open their shells open with its arms before eating it. This diet poses a serious threat to mariculture and wild shellfish fisheries. The seastar is also capable of detecting food from some distance away and will dig shallow pits to extract buried prey.
How is it controlled?
It has been found to have few natural predators Australian scientists are working with others in Japan and Russia on a biological control using parasites which infect the seastar. However, in the short-term, physical removal and the use of specially designed traps offer the only options for control.
For more on control methods see How are we trying to control marine pests?