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|Northern Pacific Seastar|
Asterias amurensis, also known as the Northern Pacific seastar and Japanese common starfish, is a seastar native to the coasts of northern China, Korea, Russia and Japan. This species has been introduced to the oceanic areas of Tasmania, southern Australia, Alaska, the Aleutian Islands, parts of Europe, and Maine. 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 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.
North Pacific Seastar Invasion in North America
The 2011 Tōhoku earthquake and tsunami with a magnitude of 9.0 struck near Oshika peninsula, sending a 133-ft. tall tsunami across 217 square miles of Japan. The tsunami was an abiotic disaster, but the resultant invading species in America, Asterias amurensis classifies as biotic disturbance. A tsunami is more immediately destructive, while an invasive species disturbance may only be addressed at a point where its negative effects become expensive or difficult to eradicate. Additionally, terrestrial and freshwater invasions have been the subject of more extensive research and study than species introduced in marine and estuarine habitats. It is important to monitor implications of invasions in these areas and their potential reach in new areas of propagation.
Japanese Tsunami Marine Debris & New Invasive Species
Alien species from Japan are introduced to North America’s west coast either on purpose when oysters are imported for farming or incidentally "hitchhiking" in ballast water. The mass influx of unknown or unwanted species from Japan after the 2011 Tohoku earthquake contributes to this existing problem. An estimated 1.5 million tons of debris, from ships to pieces of buildings, have shown up on the North American shoreline from Alaska to Southern California, carrying algae, plankton, barnacles, shellfish, echinoderms and more across the Pacific Ocean.
According to Williams College's marine sciences professor, James Carlton, about 500 foreign plants & animals have been introduced and are thriving in U.S. waters. San Francisco Bay, especially, has become a hot spot for invasive species, which have almost totally displaced native species.
In June 2012, a 188-ton dock washed up on Agate Beach in Oregon. There were at least 30 non-native species attached to it. A number of these were identified by scientists in Oregon as species that have invaded other parts of the world. John Chapman of Oregon State University's Hatfield Marine Science Center says healthy, reproductive species were found and this is a horrible thing.
Among those washed ashore was Asterias amurensis, the North Pacific sea star from Japan, which has been a troublesome invasive species in Tasmania for years. The star is a generalist species that eats scallops, cockles, oysters, clams and crustaceans as well as dead fish and fish waste. The most salient economic impact is felt when shellfish populations are depleted. The sea star is known to populate expansive areas exponentially in a relatively short period of time. In Port Phillip Bay of south Victoria, Australia, the population of 300,000 in 1999 multiplied a hundredfold in 2000 and then tripled the following year. Wild shellfisheries in Tasmania experienced losses between 0.5 to $1 million in 2000. Its voracious appetite for Fulvia tenuicostata was observed in an experiment in the Derwent Estuary of southeast Tasmania. This is one example of a depleted population of a commercial bivalve species that is directly affected by an explosion of the Northern Pacific sea star. If this pest is allowed to invade North America's shoreline it could seriously damage the fishing industry.
Impacts on Society
Invasions breed extinctions. It is vital to monitor ecological impacts from invasive species, because they can cause economic or even human health impacts. A surge in this species’ population will affect the populations of its prey and throw off normal balances in the current trophic web of Pacific coast areas. Experimental evidence has concluded that the predatory star has a major impact on juvenile bivalves. The asteroid will also attach itself to salmon traps, oyster lines and scallop longlines. In Australia, it was connected to the decline of the endangered handfish. American ecologists must pay close attention to the implications of this invasive species. As trophic webs change over time, the endangerment and loss of certain marketable sea organisms cause coastal communities to potentially lose billions of dollars. In Japan, the sea star’s population outbreaks have cost the mariculture industry millions of dollars in control measures and losses from predation.
The North Pacific sea star has already invaded Australian waters in the Derwent Estuary and Henderson Lagoon. Such a notable disturbance as a result of a Japanese tsunami has not been documented in America.
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. Poisoning the seastars or introducing a new predator to cut back their population numbers would introduce new problems, so effectiveness is not guaranteed. Early detection and prevention of reproduction remains the best solution to reducing harmful effects of invasive species. The aim of the study by Mountfort et al. was to develop a probe to test ballast water and detect the presence of this specific maritime pest. If policies on removal of ballast water are enforced, the star will not be introduced to foreign systems so frequently.
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