Asterias amurensis, also known as the Northern Pacific seastar and Japanese common starfish, is a seastar found in shallow seas and estuaries, native to the coasts of northern China, Korea, far eastern Russia, Japan, Alaska, the Aleutian Islands and British Columbia in Canada.

[1][5] Parasterias albertensis was described in 1914 from British Columbia by Addison Emery Verrill from a collection made late in the previous century and kept at the Smithsonian;[6] this taxon was synonymised by Walter Kenrick Fisher in 1930.

[1] There are two forms (or subspecies) are accepted in the World Register of Marine Species by Christopher Mah as of 2008:[1] It can grow up to 50 cm in diameter,[2][4][12] although this is exceptional and the arms usually grow to 16.1 cm, with the ratio between the length of the arm and the radius of its disc ranging from 3.6:1 to 5.9:1.

[4] It shows a wide range of colours on its dorsal side: orange to yellow, sometimes red and purple.

[2][4] The arms are unevenly covered with small, jagged-edged spines, which line the groove in which the tube feet lie, and join up at the mouth in a fan-like shape.

[12] In Russia it is found in the Peter the Great Gulf in Primorsky Krai, in the Chukotka Autonomous Okrug in the eastern Chukchi Sea to the Arctic Ocean,[12] Kamchatka,[11] the Kuril Islands, both east and west shores of Strait of Tartary and on both coasts of Sakhalin.

[13] This species has been introduced to the west coast of Tasmania in southern Australia, parts of Europe and Maine.

[14] It spread to Tasmania and Victoria as planktonic larvae in ballast water carried by commercial vessels sailing from where the species is native, such as Japan.

If the seastar is ripped apart, each arm can grow into a new animal (fissiparity) if a part of the main disk is attached.

[12] Male and female seastars release their gametes into the seawater (external fertilization),[2][12] resulting in fertilised eggs.

[2][12] These larvae float as pelagic plankton[12] from 41 to 120 days before they find and settle on a surface and metamorphose into juvenile sea stars.

This metamorphosis in larvae is stimulated by chemicals detected in the presence of adults and of tactile stimuli (feeling a surface).

Other possible parasites found associated with these seastars are the skeleton shrimps Caprella astericola, the copepod Scottomyzon gibberum, the polychaete scaleworm Arctonoe uittuta, species from the harpacticoid copepods genera Parathalestris, Thalestris, Paramphiacella and Eupelite, as well as several unidentified gammaridean amphipods and an unidentified apicomplexan living within it.

It competes with the starfish Uniophora granifera and Coscinasterias muricata, and Pacific walruses, Odobenus rosmarus ssp.

[4] A possible commensal is the bacterium Colwellia asteriadis, a new species published in 2010, which has only been isolated from Asterias amurensis hosts in the sea off Korea.

In Japan, where it is native, population outbreaks have cost the mariculture industry millions of dollars in control measures and losses from predation.

[19] It has colonised Australian waters in the Derwent Estuary, Port Phillip Bay and Henderson Lagoon in Tasmania.

[2][12] In the Derwent Estuary, the Northern Pacific seastar has been connected to the decline of the endemic endangered spotted handfish.

[2][3][23] Trials have been run to find effective removal processes including physical removal of A. amurensis, which was estimated by workshop participants to be the most effective, safe and politically attractive when compared with chemical or biological control processes.

[2] Mountfort et al. studied developing a probe to test ballast water and detect the presence of this specific maritime pest.