Ecological Impacts of Replacing One Invasive Species with Another in Rocky Intertidal Areas

Abstract

As humans continue to move about the globe with ever-increasing frequency, they carry (intentionally and unintentionally) a host of species that are being introduced to new habitats. Consequently, there is now growing concern about the impacts of these numerous invasions for native communities. Determining the implications of species invasion requires comparing the impacts of invaders to those of species that are already present within invaded communities. As species invasion becomes more common, these comparisons are increasingly required between new invasive species and previously established invasive species. Here a case study is presented of the implications of replacing one invader with a new invader. The European green crab Carcinus maenas invaded the east coast of North America in the early 1800s. As an omnivorous predator, this invader has had widespread consumptive and nonconsumptive impacts on the native community. Two decades ago, a second predatory crab, the Asian shore crab Hemigrapsus sanguineus invaded this same region. In some parts of the invaded range, H. sanguineus has now replaced C. maenas as the dominant intertidal predator. The interactions between these two species that have likely contributed to this species replacement are reviewed. Then the implications of this species replacement for the native community are examined, specifically with regards to the differences in consumptive and nonconsumptive effects of these two predators, including both direct and indirect effects. Finally, population density and differences in habitat use by these two species are incorporated to predict how their impacts vary spatially along a latitudinal gradient throughout the invaded range.