The Northern Pacific Seastar (Asterias amurensis) is a marine organism recognized by its five tapering arms extending from a small central disk. It typically displays coloration ranging from orange to yellow, sometimes with red and purple pigmentation on its upper surface. A distinguishing feature is the often upturned tips of its arms. While it can reach up to 50 centimeters in diameter, it is usually much smaller.
Defining the Native Range
The native distribution of Asterias amurensis is confined to the shallow, temperate coastal waters of the Northwest Pacific Ocean. This area encompasses the shorelines of East Asian nations, including Japan, the Korean Peninsula, Northern China, and the far eastern coasts of Russia.
The precise geographic limits include the Sea of Japan, the Yellow Sea, and the coastal regions surrounding the Okhotsk Sea. The species prefers shallow, sheltered areas in the intertidal zone but can be found at depths reaching up to 220 meters.
Its historical range is characterized by relatively cold water temperatures, typically preferring an environment around 7 to 10 degrees Celsius.
Key Biological Characteristics
The biological success of the Northern Pacific Seastar stems from its massive reproductive capacity. A single mature female can release an estimated 10 to 25 million eggs annually.
Following external fertilization, the offspring enter a prolonged planktonic larval stage that can last anywhere from 41 to 120 days. These free-swimming larvae, known as bipinnaria and brachiolaria, are pelagic. This lengthy larval duration is a primary factor in the species’ ability to disperse over considerable distances, carried by ocean currents.
The seastar also exhibits physiological tolerance to varying marine conditions. It is eurythermal, surviving a temperature range documented from 0 to 25 degrees Celsius. Furthermore, it is euryhaline, tolerating salinities between 18.7 and 41.0 parts per thousand.
This high tolerance allows the seastar to thrive in estuarine habitats where salinity fluctuates due to freshwater runoff. Once settled, the seastar becomes a voracious predator.
It uses its tube feet to pull apart the shells of bivalve molluscs (like mussels, clams, and oysters), then everts its stomach through its mouth to digest prey externally. The predatory diet is broad, also including gastropods, barnacles, crustaceans, and other invertebrates, which allows the species to exert significant pressure on local benthic communities. Its rapid growth, reaching sexual maturity at around one year of age and a diameter of 10 centimeters, further compounds its ability to establish quickly.
Global Presence as an Introduced Species
Outside of its native Asian waters, the seastar has developed established populations in several regions globally, primarily through human activity. The most widespread and ecologically recognized introductions have occurred in Southern Australia, particularly in the Derwent Estuary in Tasmania and Port Phillip Bay in Victoria. These regions have experienced significant population booms since the species was first detected in the 1980s.
The primary mechanism responsible for the seastar’s global spread is commercial shipping. The long-lived planktonic larval stage makes the species susceptible to being drawn into and transported within the ballast water tanks of large vessels. When the ship discharges this water in a new port, the larvae are released into a foreign environment where they can settle and establish a new population.
Another vector for human-assisted dispersal is the fouling of ship hulls, where juvenile or adult seastars can attach themselves to the outside of a vessel. The movement of equipment and stock related to aquaculture activities has also been implicated in the secondary spread of the seastar. The combination of these human-mediated transport mechanisms has allowed Asterias amurensis to become a global marine species.