Non-lethal effects of an invasive species in the marine environment: the importance of early life-history stages

Abstract

Studies examining the eVects of invasive species have focussed traditionally on the direct/lethal eVects of the invasive on the native community but there is a growing recognition that invasive species may also have non-lethal eVects. In terrestrial systems, non-lethal eVects of invasive species can disrupt early life-history phases (such as fertilisation, dispersal and subsequent establishment) of native species, but in the marine environment most studies focus on adult rather than early life-history stages. Here, we examine the potential for an introduced sessile marine invertebrate (Styela plicata) to exert both lethal and non-lethal eVects on a native species (Microcosmus squamiger) across multiple early life-history stages. We determined whether sperm from the invasive species interfered with the fertilisation of eggs from the native species and found no eVect. However, we did Wnd strong eVects of the invasive species on the post-fertilisation performance of the native species. The invasive species inhibited the settlement of native larvae and, in the Weld, the presence of the invasive species was associated with a tenfold increase in the post-settlement mortality of the native species, as well as an initial reduction of growth in the native. Our results suggest that larvae of the native species avoid settling near the invasive species due to reduced postsettlement survival in its presence. Overall, we found that invasive species can have complex and pervasive eVects (both lethal and non-lethal) across the early life-history stages of the native species, which are likely to result in its displacement and to facilitate further invasion.