1998. It has become an invasive species in Australia and is on the Invasive Species Specialist Group list of the world's 100 worst invasive species. Ecology Habitat They prefer a slightly cold environment of about 7–10 °C. The optimum temperature is also said to be 9–13 °C. It has a temperature tolerance of 0–25 °C according to one source, or 5–20 °C according to another. It is able to tolerate a large range of salinities, from 18.7–41.0 ppt., and can survive in estuaries. It has been found at a maximum depth of 220m. It prefers shallow, sheltered areas. Adults are found on a wide range of substrates, including kelp forests, mud, sand, pebbles, rock, flotsam, nets and artificial substrates. It is not found in areas of high wave action or on reefs. Behaviour These seastars move towards light. The adults are mobile with a top speed of 20 cm/minute. Tagged seastars in Tokyo Bay, Japan, logged maximum travel distances 2.5 km in 32 days (78m/day) in the west of the bay, and 8.1 km in 129 days (62.8m/day) at the east. The population goes through boom-and-bust cycles in Japan, where it can swarm on occasions; during swarms the adults can float on the sea surface due to air retained within the body cavity. The population is mixed, with different age groups found intermingled. The animals can survive at least four years in the wild in Japan, but it is estimated that most live to two to three years. If the seastar is ripped apart, each arm can grow into a new animal (fissiparity) if a part of the main disk is attached. This is not entirely uncommon. Development Male and female seastars release their gametes into the seawater (external fertilization), resulting in fertilised eggs. These go through gastrulation and become larvae. Once these begin to feed they are called bipinnaria, this stage then grows into the brachiolaria after growing five arms, three fused with the central disk. The development is temperature-dependant. These larvae float as pelagic plankton from 41 to 120 days before they find and settle on a surface and metamorphose into juvenile sea stars. This metamorphosis in larvae is stimulated by chemicals detected in the presence of adults and of tactile stimuli (feeling a surface). The first year these juveniles grow 6mm a month, thereafter they grow 1–2mm a month. Males and females can be sexually mature when