Northern Pacific seastar in Australia
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The Northern Pacific seastar (Asterias amurensis) is an invasive species in Australia.
This seastar is native to the coasts of northern China, North Korea, South Korea, Russia and Japan, and distribution of this species into other countries has increased. It is on the Invasive Species Specialist Group list of the world's 100 worst invasive species. They can be transmitted to waters around the world via seawater in live fish trade, via recreational boats, in ballast water, and on the hulls of ships.[1]
The species prefers waters temperatures of 7°C to 10°C, but it has adapted to Australian waters of around 22°C, and usually found in shallow waters of protected coasts. It is able to tolerate a wide range of temperature and salinity, so is frequently found in estuaries and on muddy, sandy or rocky sheltered areas of intertidal zones.[1]
Detection, habitat and behaviour in Australia
Asterias amurensis was first seen in Tasmanian coastal waters in 1986.[2] Their presence has been recorded in the state from as far north as Banks Strait (between Cape Portland and Clarke Island[3]) and south to Recherche Bay, with the highest population densities in sheltered waters in south-east Tasmania, particularly the Derwent Estuary.[4]
It then spread northwards,[4] and was detected in Port Philip Bay, Victoria, where it was observed to reach up to 12 million individuals over a two-year span,[1] and is now considered established there. It has also been seen in San Remo, Anderson Inlet, Waratah Bay, Tidal River and the Gippsland Lakes area, but measures are being taken to ensure that they do not get established in these areas.[4]
In Australian waters, spawning occurs between July and October,[1] and the female seastar can carry 10 to 25 million eggs.[4] It is a voracious predator, consuming bivalves, gastropod molluscs, barnacles, crustaceans, sea worms, echinoderms, ascidians, sea urchins, sea squirts and other seastars, including those of its own species if other supplies are exhausted. Its preferred foods are clams, mussels and scallops, but will also eat dead fish and fish waste.[1]
Although the species prefers shallow, sheltered areas, it has also been observed in other habitats, including on rocky reefs and bedrock, and, in its native range around Japan, at depths of up to 200 metres (660 ft).[4]
Impact
The Northern Pacific seastar is considered a serious pest of native marine organisms in Australia, and is a major factor in the decline of the critically endangered spotted handfish. It preys on the handfish eggs, and/or on the sea squirts (ascidians)[1] that help to form the substrate that the fish spawn on.[2] It is also considered a mariculture pest, as it settles on the lines used to grow scallops, mussels and oysters, as well as salmon cages.[1]
In 2005, a two-year study identified Asterias amurensis as "one of the ten most damaging potential domestic target species, based on overall impact potential (economic and environmental)", and as having a "reasonably high impact/or invasion potential".[1]