Range expansion of Asterias amurensis along the east coast of Victoria via larval dispersal

The Northern Pacific seastar (Asterias amurensis) is an introduced marine pest, native to the NW Pacific, and likely to have been first introduced to SE Tasmania from Japan via ballast water in the 1980s, and subsequently to... [ view full abstract ]

The Northern Pacific seastar (Asterias amurensis) is an introduced marine pest, native to the NW Pacific, and likely to have been first introduced to SE Tasmania from Japan via ballast water in the 1980s, and subsequently to Port Phillip Bay from Tasmania in the mid-1990s. Populations of A. amurensis have subsequently been recorded along the east coast of Victoria at Andersons Inlet in 2003, San Remo (Western Port) in 2011, and at Tidal River (Wilsons Promontory) in 2012. It is unclear whether these outbreaks represent a natural range expansion of the population within Victorian waters, facilitated by planktonic larval dispersal, or are the product of physical translocation of larval and adult seastars by anthropogenic vectors. This study used a combination of plankton surveys and hydrodynamic modelling to examine the distribution of A. amurenis larvae in coastal waters between Port Phillip Bay and Port Welshpool in eastern Victoria. The source of A. amurensis populations at Tidal River and San Remo was identified using polymorphic microsatellite markers collected from potential source populations in Port Phillip Bay, SE Tasmania and Japan. A. amurensis larvae were detected in coastal waters between Port Phillip Bay and Wilsons Promontory. This finding is supported by hydrodynamic modelling of buoyant particles simulating the behaviour of larvae exported from the bay, and the influence of the prevailing currents in Bass Strait. Populations at Tidal River were most closely related to A. amurensis populations in the southern part of Port Phillip Bay consistent with the hypothesis that new populations of A. amurensis originated from larvae exported from the bay, by tidal flushing, and subsequently dispersed eastwards along the coast. The pattern of A. amurensis incursions along the east coast of Victoria is therefore entirely consistent with natural range expansion via larval dispersal; with Port Phillip Bay as the main source of larvae in the region.