When worlds collide
Interactions between multiple invasive alien species might increase their ecological impacts, yet relatively few studies have attempted to quantify the effects of facilitative interactions on the success and impact of aquatic IAS. In the present study performed with TransNational Access funds from AQUACOSM project, Coughlan et al. assessed a potential facilitative interaction between a predatory invasive fish, the Ponto-Caspian round goby (Neogobius melanostomus), and an invasive bivalve, the Asian clam (Corbicula fluminea). They compared N. melanostomus functional responses (feeding-rates under different prey densities) to a co-occurring endangered European native analogue fish, the bullhead (Cottus gobio), in the presence of increased levels of habitat complexity driven by the accumulation of dead C. fluminea biomass that persists within the environment (i.e. 0, 10, 20 empty bivalve shells). Habitat complexity significantly influenced predation, with consumption in the absence of shells being greater than where 10 or 20 shells were present. However, at the highest shell density, invasive N. melanostomus maximum feeding-rates and functional response ratios were substantially higher than those of native C. gobio. Further, the Relative Impact Potential metric, by combining per capita effects and population abundances, indicated that higher shell densities exacerbate the relative impact of the invader. It therefore appears that N. melanostomus can better tolerate higher IAS shell abundances when foraging at high prey densities, suggesting the occurrence of an important facilitative interaction. These data are thus fully congruent with field data that link establishment success of N. melanostomus with the presence of C. fluminea. Overall, invader-driven benthic habitat complexity can alter the feeding-rates and thus impacts of predatory fishes, and highlight the importance of inclusion of abiotic factors in impact prediction assessments for IAS.
Published in Science of the Total Environment
