Marine Biology

, Volume 144, Issue 4, pp 747–756

Interaction and impacts of two introduced species on a soft-sediment marine assemblage in SE Tasmania


    • School of Zoology and Tasmanian Aquaculture and Fisheries InstituteUniversity of Tasmania
    • Centre for Research on Introduced Marine PestsCSIRO Marine Research
    • Department of ZoologyUniversity of Melbourne
  • C. R. Johnson
    • School of Zoology and Tasmanian Aquaculture and Fisheries InstituteUniversity of Tasmania
  • C. L. Hewitt
    • Centre for Research on Introduced Marine PestsCSIRO Marine Research
    • Ministry of Fisheries
  • G. M. Ruiz
    • Smithsonian Environmental Research Center
Research Article

DOI: 10.1007/s00227-003-1223-4

Cite this article as:
Ross, D.J., Johnson, C.R., Hewitt, C.L. et al. Marine Biology (2004) 144: 747. doi:10.1007/s00227-003-1223-4


Introduced species are having major impacts in terrestrial, freshwater and marine ecosystems world-wide. It is increasingly recognised that effects of multiple species often cannot be predicted from the effect of each species alone, due to complex interactions, but most investigations of invasion impacts have examined only one non-native species at a time and have not addressed the interactive effects of multiple species. We conducted a field experiment to compare the individual and combined effects of two introduced marine predators, the northern Pacific seastar Asterias amurensis and the European green crab Carcinus maenas, on a soft-sediment invertebrate assemblage in Tasmania. Spatial overlap in the distribution of these invaders is just beginning in Tasmania, and appears imminent as their respective ranges expand, suggesting a strong overlap in food resources will result from the shared proclivity for bivalve prey. A. amurensis and C. maenas provide good models to test the interaction between multiple introduced predators, because they leave clear predator-specific traces of their predatory activity for a number of common prey taxa (bivalves and gastropods). Our experiments demonstrate that both predators had a major effect on the abundance of bivalves, reducing populations of the commercial bivalves Fulvia tenuicostata and Katelysia rhytiphora. The interaction between C. maenas and A. amurensis appears to be one of resource competition, resulting in partitioning of bivalves according to size between predators, with A. amurensis consuming the large and C. maenas the small bivalves. At a large spatial scale, we predict that the combined effect on bivalves may be greater than that due to each predator alone simply because their combined distribution is likely to cover a broader range of habitats. At a smaller scale, in the shallow subtidal, where spatial overlap is expected to be most extensive, our results indicate the individual effects of each predator are likely to be modified in the presence of the other as densities increase. These results further highlight the need to consider the interactive effects of introduced species, especially with continued increases in the number of established invasions.

Copyright information

© Springer-Verlag 2003