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Nonindigenous species are increasingly recognized as altering marine and estuarine communities,
causing significant changes in abundance and distribution of native species. Such effects are of
particular concern to coastal fisheries. We experimentally determined the effect of the nonindigenous
European green crab, Carcinus maenas, upon the stepped venerid clam, Katelysia scalarina, the
basis for a fledgling clam fishery in Tasmania, Australia. First, we observed a trend of decreased
juvenile ( < 13-mm shell length or SL) abundance of K. scalarina at sites with C. maenas relative to
those without this invasive predator. Additionally, relative predation intensity on these juveniles was
significantly higher in invaded areas. To better understand the dynamics of predation by this invader,
we conducted a number of manipulative experiments. In cage experiments testing per capita
predation rates, we found that: (1) of the various sizes of C. maenas, large C. maenas were the most
significant predators; (2) the smallest size class of K. scalarina tested (6