Native spider crab causes high incidence of sub-lethal injury to the introduced seastar Asterias amurensis

Abstract

While population expansion of Asterias amurensis in Tasmania continues, the occurrence of arm loss among individuals in the Derwent Estuary suggests the presence of predators (Grannum et al. 1996, Lawrence et al. 1999, J. Ross unpub. data). Predatory invertebrates such as the large asteroid Coscinasterias muricata, and decapod crustaceans including the hermit crab (Trizopagurus strigimanus), horse crab (Cancer novaezealandiae) and spiny lobster (Jasus edwardsii), have been implicated as predators of A. amurensis based on observations in aquaria (Parry et al. 2000, L. Turner pers. comm.). Observations of predation in situ are rare with only another asteroid C. muricata witnessed to prey on A. amurensis, however this1 INTRODUCTIONEstablishment of introduced species in new environments is dependent on the outcomes of interactions with the recipient community (e.g. Pimm 1989, Vermeij 1991, reviewed by Lodge 1993). In the absence of adapted natural predators, introduced species may proliferate unopposed and reach very high population levels, i.e. the “predatory release hypothesis” (e.g. Crawley 1987). The northern Pacific seastar, Asterias amurensis (Lütken), was inadvertently introduced to Tasmanian waters sometime in the 1980s where it has undergone rapid population increase particularly in the Derwent Estuary where it has become the dominant benthic predator (Buttermore et al. 1994, Grannum et al. 1996, Byrne et al. 1997, Ross et al. 2002, 2003). While predators of A. amurensis are known from the northern Pacific (i.e. Alaskan king crabs, see Mikulich & Berulina 1972; and other asteroids, see McLoughlin & Bax 1993) little is known about predators within the seastar’s introduced range.