Assessing biotic interactions between a non-indigenous amphipod and its congener in a future climate change scenario.
To evaluate the impact of successful invasions of marine ecosystems by nonindigenous species (NIS) in a future climate change scenario, we analysed how an increase in temperature may affect biotic interactions between resident species and newcomers. In this context, we examined the effect of temperature on interference competition (i.e. displacement) between two ecologically-similar caprellid species that co-occur in the Portuguese Atlantic archipelago of Madeira: the NIS Caprella scaura (Templeton, 1836) and its congener Caprella equilibra (Say, 1818). Mesocosm experiments were used to assess the interaction between the two species and the effects of warmer ocean waters on this interaction. Specifically, we investigated the effect of an increase in temperature on: (i) survivorship and intraspecific displacement of the NIS C. scaura, (ii) survivorship and interspecific displacement when this NIS and its congener C. equilibra coexisted at similar densities, and (iii) survivorship and interspecific displacement in the two species when the density of NIS is higher compared to its congener. Furthermore, we explored differences in the heart rate of the two species as proxy for physiological condition. Our results showed that in a future scenario of ocean warming for Madeira Island (29°C), survivorship and intraspecific displacement of C. scaura most likely will not be affected. The survivorship of the congener C. equilibra will not be compromised, but its displacement will be affected by a combination of temperature and density of NIS. Overall, our results showed that warming exacerbates interspecific interactions between the two caprellid species suggesting that climate change can modify species distribution among habitats, potentially affecting community structure and diversity. The results of this study highlight the importance of biotic interactions and environmental context to predict and assess NIS success and potential impacts on resident species in the perspective of climate change.