Northern Pacific seastar
Encyclopedia
Asterias amurensis, commonly called the northern Pacific starfish, is an invasive species
in Australia
, and native to the coasts of northern China
, North Korea
, South Korea
, Russia
and Japan
. Distribution of this species into other countries has increased. 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 larva
e in ballast
water for ships. The ships suck in the ballast water containing seastar larvae, in a port such as one in Japan, and let it out in a port such as one in Tasmania
, the larvae come out with the water, and metamorphose into juvenile sea stars.
occurs from July to October at temperatures of 10°C to 12°C. Fertilized eggs develop into free-swimming larvae that live in the water for around 90 days before settling and metamorphosing into juvenile seastars. In one year the northern Pacific seastar is capable of increasing its diameter by 8 cm; when fully grown the northern Pacific seastar lives up to five years, and can reach sizes up to 40 to 50 cm in diameter. Larval survival is constrained by temperature and salinity of the surrounding marine habitat, with the optimal ranges respectively 8°C to 16°C, and 3‰ to 8.75‰. Generally, seastars are sensitive to salinity
fluctuations, and are unlikely to be found in places of high salinity. In Japan its numbers increase and reach outbreak proportions for two to three years; outbreaks have been found to occur in three or ten year cycles.
Native to the coasts of northern China, Korea, Russia and Japan, the northern Pacific seastar lives in waters between 7 °C and 22 °C. It lives in mainly shallow water, but also is found as deep as 200 metres. It is rarely found on reefs or high wave action areas, instead sitting on mud, sand or pebbles.
In Tasmania, due to the plague of these seastars, hunting days have been organized, where volunteers work together to physically remove as many of the seastars as possible. Efforts of this kind in 1993 resulted in the collection of more than 30,000 seastars. During the first attempts to remove the seastar from Tasmania, many of the seastars that were captured were cut up and thrown back into the sea. Unfortunately, each part that was thrown back was able to regenerate and grow a new seastar as long as it had part of the central disc remaining.
Seastar poisons are not specific and in the ocean, could damage many other natural marine communities. Also, the amount of chemicals needed to poison seastars in estuaries would be uneconomical, and very impractical. In Australia, northern Pacific seastars don't have any pathogen
s, though in Japan, northern Pacific seastars are attacked by a unicelled animal called Orchitophrya. Orchitophrya invades seastars' testes, kills sperm, and castrates the seastar. However scientists later discovered that Orchitophrya doesn't usually invade all 10 of the seastar's testes and doesn't have the effect hoped for.
The northern Pacific seastar has also been found in Port Phillip Bay
, Victoria
, for some years now. Interestingly, the seastar has migrated inland in the Maribyrnong River
, reaching as far inland as Essendon
. The Maribyrnong is a salty river (previously known as Saltwater River), but finding the seastar this far inland is unusual.
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, and native to the coasts of northern China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, North Korea
North Korea
The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea...
, South Korea
South Korea
The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. Distribution of this species into other countries has increased. 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 larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e in ballast
Sailing ballast
Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...
water for ships. The ships suck in the ballast water containing seastar larvae, in a port such as one in Japan, and let it out in a port such as one in Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
, the larvae come out with the water, and metamorphose into juvenile sea stars.
Reproduction
In Australia spawningSpawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
occurs from July to October at temperatures of 10°C to 12°C. Fertilized eggs develop into free-swimming larvae that live in the water for around 90 days before settling and metamorphosing into juvenile seastars. In one year the northern Pacific seastar is capable of increasing its diameter by 8 cm; when fully grown the northern Pacific seastar lives up to five years, and can reach sizes up to 40 to 50 cm in diameter. Larval survival is constrained by temperature and salinity of the surrounding marine habitat, with the optimal ranges respectively 8°C to 16°C, and 3‰ to 8.75‰. Generally, seastars are sensitive to salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
fluctuations, and are unlikely to be found in places of high salinity. In Japan its numbers increase and reach outbreak proportions for two to three years; outbreaks have been found to occur in three or ten year cycles.
Native to the coasts of northern China, Korea, Russia and Japan, the northern Pacific seastar lives in waters between 7 °C and 22 °C. It lives in mainly shallow water, but also is found as deep as 200 metres. It is rarely found on reefs or high wave action areas, instead sitting on mud, sand or pebbles.
In Tasmania, due to the plague of these seastars, hunting days have been organized, where volunteers work together to physically remove as many of the seastars as possible. Efforts of this kind in 1993 resulted in the collection of more than 30,000 seastars. During the first attempts to remove the seastar from Tasmania, many of the seastars that were captured were cut up and thrown back into the sea. Unfortunately, each part that was thrown back was able to regenerate and grow a new seastar as long as it had part of the central disc remaining.
Seastar poisons are not specific and in the ocean, could damage many other natural marine communities. Also, the amount of chemicals needed to poison seastars in estuaries would be uneconomical, and very impractical. In Australia, northern Pacific seastars don't have any pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s, though in Japan, northern Pacific seastars are attacked by a unicelled animal called Orchitophrya. Orchitophrya invades seastars' testes, kills sperm, and castrates the seastar. However scientists later discovered that Orchitophrya doesn't usually invade all 10 of the seastar's testes and doesn't have the effect hoped for.
The northern Pacific seastar has also been found in Port Phillip Bay
Port Phillip
Port Phillip Port Phillip Port Phillip (also commonly referred to as Port Phillip Bay or (locally) just The Bay, is a large bay in southern Victoria, Australia; it is the location of Melbourne. Geographically, the bay covers and the shore stretches roughly . Although it is extremely shallow for...
, Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
, for some years now. Interestingly, the seastar has migrated inland in the Maribyrnong River
Maribyrnong river
The Maribyrnong River rises about 50 km north of Melbourne, Victoria , near Mount Macedon. It flows generally southward and combines with the Yarra River to flow into Port Phillip....
, reaching as far inland as Essendon
Essendon, Victoria
Essendon is a suburb in Melbourne, Victoria, Australia, 10 km north-west from Melbourne's central business district. Its Local Government Area is the City of Moonee Valley...
. The Maribyrnong is a salty river (previously known as Saltwater River), but finding the seastar this far inland is unusual.