Impact of the northern Pacific seastar Asterias amurensis on soft sediment assemblages, including commercial species, in southeast Tasmania

摘要: Introduced species are having major impacts in terrestrial, freshwater and marine ecosystems worldwide. In Australia, the introduced northern Pacific seastar (Asterias amurensis) was first recorded southeast Tasmania 1986, where it has become the dominant invertebrate predator Derwent River Estuary. Despite indirect indications based on foraging behavior, stomach contents, estimates of feeding electivity that suggest potential for considerable impact native benthic marine assemblages, of not previously been examined directly or quantitatively either its range. Because the absence baseline data prior to arrival presence other anthropogenic stressors estuary, estimating is difficult. To overcome these difficulties limitations any one method of impact assessment, I used multiple methods at different scales provide independent tests impact: (a) experiments which density is manipulated at several sites immediately beyond current range seastar; (b) experiments in manipulated following recruitment prey; ( c) experiments both seastars another benthic predator (Carcinus maenas) examine their interaction; (d) comparative analysis prey taxa sediments stomachs; e) spatially hierarchical surveys relationship between soft sediment assemblages abundance Tasmania. The combination provide, time, a robust estimate the impact seastar. In Estuary occurs high densities, live adult bivalves rare despite numerous recent remains (intact shells) adults. Experiments conducted current range clearly demonstrated large Asterias amurensis adult bivalve populations commercial cockles Fu/via tenuicostata Katelysia rhytiphora particular. Manipulative also Asterias amurensis survivorship bivalve recruits estuary, effectively arresting significant events. Observations diet prey switching show while clear food preferences, generalist predator able switch other when preferred become relatively rare. This finding results that the exact nature effects site time specific given inherent natural variability sediment assemblages seastar's responses them. the event spatial overlap with predatory European green crab (Care us maenas), predators may coexist because resource partitioning basis size and/or habitat requirements, impact on bivalves be greater species. I use from experimental manipulations, feeding observations large scale provide broad synthesis immediate predicted on native species. There strong evidence predation by responsible decline subsequent rarity species that just below surface Recent modelling dispersal larvae indicates majority larvae produced estuary likely advected (Morris & Johnson prep). It seems should densities areas Tasmanian coast attain levels occur Estuary, there large direct particularly populations bivalves (including species) under surface. Given the ability exploit resources importance of bivalves as functional component systems, predict broader direct and indirect assemblages. Overall, important consequences of the establishment spread this warrant management efforts control impact.