Northern Pacific sea stars are found throughout parts of the Pacific Ocean near Japan, Russia, Northern China, and Korea as a native species. However, this species has also been introduced to oceanic habitats near parts of the southern Australian coast (especially Tasmania), Alaska and the Aleutian Islands, Europe, and the state of Maine. ("Asterias amurensis (Japanese seastar)", 2012; "Ocean Biogeographic Information System", 2012; Byrne, et al., 1997; Stevens, 2012)
Northern Pacific sea stars live in estuarine, intertidal, and coastal zones and prey on other marine inhabitants in or on the substrate. They are found near protected areas of coasts, far away from areas of the ocean with high wave action, at depths up to 220 meters. They prefer a slightly cold environment of about 7-10ºC; however, this species has adapted to the warmer waters of the Australian coast, which average about 22ºC. It can survive in a temperature range of 0–25ºC. Due to their presence in estuarine habitats, these sea stars are able to tolerate a large range of salinities, from 18.7-41.0 ppt. ("Asterias amurensis (Japanese seastar)", 2012; Stevens, 2012)
Northern Pacific sea stars have five arms, all ending in small, upward-turned tips. Each of these arms joins in the center of the organism to form a central disc. This species shows a wide range of colors, from orange to yellow, and sometimes purple on their dorsal side. Irregularly arranged spines run down the length of each arm. A row of spines from each arm come together near the mouth area, creating a fan-like appearance. Spines also line the ventral groove of each arm, where the tube feet are found. This species can grow to be up to 50 cm in diameter. ("Asterias amurensis (Japanese seastar)", 2012; Stevens, 2012)
Male and female sea stars release their respective gametes in to the aquatic environment. The gametes come together to form a fertilized egg, which undergoes holoblastic and radial cleavage followed by gastrulation, completing the beginning stages of larval development. The larva begins to feed once the gastrovascular canals are formed, and at this stage is called a bipinnaria. This stage later develops brachiolar arms, with three of them combining with a central adhesive disk to form the brachiolar complex. This marks the transition of the larva into the brachiolaria state. A brachiolarian larva can remain in the water column for about 120 days before it finally settles and undergoes metamorphosis into the adult sea star. Metamorphosis is induced by the detection of metamorphic inducing factors by the adhesive papillae on the brachiolar arms, such as chemical cues from adult sea stars in the environment. It takes a larva as little as 41 days to about 120 days, from the time of fertilization, to develop into an adult sea star. This process is all dependent upon the temperature of the water in which the sea star is developing; the warmer the water, the faster the rate of development. (Byrne, et al., 1997; Paik, et al., 2005; Stevens, 2012)
Female Northern Pacific sea stars release their eggs into the surrounding marine environment; they are then externally fertilized by sperm released by male sea stars. This species reproduces seasonally and spawns during the months of January to April in Japan and during the months of June to October in Russia and Australia. ("Asterias amurensis (Japanese seastar)", 2012; Stevens, 2012)
Sexual maturity occurs in both males and females when they are 3.6-5.5 cm in length. Females can be identified for 5-6 months of the year due to the presence of their maturing ovaries. Mature ovaries are characterized by the constant release of eggs as well as their orange color. Females are capable of carrying about 10-25 million eggs. Males are also reproductively mature for about 6 months of the year, with maturity being characterized by the yellowish-brown color of the testes. These sea stars have ectosomatic organs, meaning that the pores for gamete expulsion are in direct contact with the marine environment. As gametes are released, they are replaced by constantly ongoing gametogenesis within the gonads. Spawning usually occurs in the late winter and early spring months, continuing into the summer. ("Asterias amurensis (Japanese seastar)", 2012; Byrne, et al., 1997; Paik, et al., 2005; Stevens, 2012)
The average lifespan of a sea star is around 10 years, although many sea star species are able to live to about the age of 50. There is no specific information available regarding the lifespan of Northern Pacific sea stars. (Uscian, 2006)
These sea stars exhibit positive phototactic behavior, moving toward light. In situations where part of the organism is shaded and part is illuminated, it has been seen that the animal moves towards the illuminated area. As they move, the animals exhibit what is known as a “typical advancing posture". This means that the sea star moves with a particular ray of its body in a certain direction and the rest of the organism slowly follows. The adult and juvenile forms of these sea stars both have limited motility. When they do move, they step using their tube feet. However, larval stages are free-swimming and are known to travel using water currents. (Stevens, 2012; Yoshida and Ohtsuki, 1968)
There is no home range information available for Northern Pacific sea stars.
Northern Pacific sea stars are able to perceive light stimuli and are positively phototactic. As previously mentioned, when four of five arms are shaded, a sea star will move with its illuminated ray forward. All other documented information about the communication and perception abilities of these sea stars regards sensory interactions between larval and adult forms. Larvae are capable of sensing metamorphosis inducing factors expelled by adults via use of neural cells that are held within the adhesive papillae on the external surface of the brachiolar arms. (Murabe, et al., 2007; Yoshida and Ohtsuki, 1968)
Northern Pacific sea stars are known to be voracious predators with a varied diet, essentially eating any type of animal that they encounter. Bivalves, such as mussels, scallops and clams compromise the largest part of this species' diet. They are known to pull apart the shell of these organisms with their arms, and then evert their stomachs into the shell cavity to digest their prey. This species also preys on gastropods, crabs, and barnacles. Occasionally, they have been seen exhibiting cannibalistic behavior when food sources are particularly low. This species has also been observed digging out buried prey from under the substrate, and feeding on algae. ("Introduced Marine Aquatic Invaders - A Feld Guide", 2012)
Northern Pacific sea stars are not generally preyed upon by other organisms. However, they may occasionally be eaten by Japanese sun stars (Solaster paxillatus). In Alaska, king crabs are known to feed on this species, and in laboratory settings, snails in the genus Charonia (tritons) have shown a preference for this species, as opposed to feeding on other marine life. ("Asterias amurensis Feeding and Predators", 2012)
Northern Pacific sea stars are an invasive species in some areas and an obligate predator whose presence has a great impact on benthic infauna, including mollusks, crustaceans, echinoderms, and other organisms that are preyed upon by this sea star. This species is known to host the bacterium Colwellia asteriadis, although negative effects on the sea star due to the presence of this microbe have not been described. ("National Control Plan for the Northern Pacific Seastar Asterias amurensis", 2008; Choi, et al., 2010)
There are no known positive economic effects of Asterias amurensis on humans.
The negative economic effects of Northern Pacific sea stars are extensive. In their native Japan, they have devastated the shellfish industry. In Australia, the economic effects of the species are still being fully evaluated, but it is thought that if their spread continues, the soft sediment communities along the coast of Australia may be compromised. It is evident that several fisheries have been negatively impacted – there has been an estimated one billion dollar loss in the industry in Tasmania. Because these fishing industries are important to the economy of the region, several “sea star hunting days” have been organized in which several thousand sea stars have been removed from the coasts. Northern Pacific sea stars are also on the Global Invasive Species Database's list of the 100 Worst Invasive Species. ("National Control Plan for the Northern Pacific Seastar Asterias amurensis", 2008; Stevens, 2012)
This species hs no special conservation status.
Foram Shah (author), The College of New Jersey, Shikha Surati (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Jeremy Wright (editor), University of Michigan-Ann Arbor.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
fertilization takes place outside the female's body
union of egg and spermatozoan
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
uses sight to communicate
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