Development and evaluation of a PCR-based test for detection of Asterias (Echinodermata : Asteroidea) larvae in Australian plankton samples from ballast water

The northern Pacific seastar, Asterias amurensis, spread to Tasmania in the 1980s from its native range in the North Pacific. The seastar has subsequently established in Port Phillip Bay on mainland Australia. Transportation of larvae in ballast water is one vector for these introductions and is likely to contribute to additional range expansion of this species. Larval identification methods are critical to assess risks of further transport to uninvaded ecosystems; however, morphological identification of larval asteroids is impractical and unreliable. Therefore, we have developed a sensitive PCR-based method that specifically detects Asterias DNA. The method works on isolated seastar larva, mixed plankton and ballast water samples. Trials using uninfected ballast water samples spiked with known numbers of A. amurensis larvae indicate that the technique can detect single larva in 200 mg of plankton. The test also detects other Asterias species; therefore, discrimination between seastars within the genus Asterias was accomplished using denaturing gradient gel electrophoresis (DGGE). Currently, this method is being used to facilitate research on ballast water transport, distribution and the ecology of A. amurensis larvae. The general approach can be expanded to provide a rapid and cost-effective approach for detecting a suite of marine species in ballast water and environmental samples.