Northern Pacific sea star
From Biocrawler, the free encyclopedia.
Asterias amurensis, commonly referred to as the northern Pacific sea star, is native to the coasts of northern China, North Korea, South Korea, Russia and Japan. Distribution of this species has increased, into other countries. Based on the distribution of northern Pacific sea star 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 sea star 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 metamophasize into juvenile sea stars.
Reproduction
In Australia spawning occurs from July to October at temperatures of 10˚-12˚ C. Fertilised eggs develop into free-swimming larvae that live in the water for around 90 days, before settling and metamorphosizing into juvenile sea stars. In one year the sea star is capable of increasing its diameter by 8 cm; at fully grown, the northern Pacific sea star 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˚ to 16˚ C, and 3‰ to 8.75‰. Generally, sea stars are sensitive to salinity fluctuations, and is unlikely to be found in places as such. Northern Pacific sea stars live up to five years. In Japan its numbers increase and reach outbreak for two to three years; outbreaks tend to occur in three or ten year cycles.
Habitat
Native to the coasts of northern China, Korea, Russia and Japan, the northern Pacific sea star lives in waters between 7˚ 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 pebble substrates.
Plagues
In Tasmania, due to the plague of sea stars, hunting days have been organised, where volunteers work together to physically remove as many of the sea stars as possible. Efforts of this kind in 1993 resulted in the collection of more than 30,000 sea stars.
Sea star poisons are not specific and in the ocean, could damage many other natural marine communities. Also, the amount of chemicals needed to poison sea stars in estuaries would be very expensive, and very impractical. In Australia, northern Pacific sea stars don't have any pathogens, though in Japan, northern Pacific sea stars are attacked by unicelled animal, called Orchitophrya. Orchitophrya invades sea stars' testes, and kills sperm and castrates the sea star. However scientists later found out that Orchitophrya don't usually invade all 10 of the sea star's testesm and it's unlikely Orchitophrya will have the effect scientists had hoped for.
