Non-native species outperform natives in coastal marine ecosystems subjected to warming and freshening events

Aims: Contemporary climate change and biological invasions are two main drivers of biodiversity redistribution. Interactive effects between these drivers have been reported in a variety of studies, yet results are conflicting. Some studies find that contemporary climate change facilitates the spread and success of non-native species, especially those with broad physiological tolerances. Other studies conclude that non-natives are vulnerable to current and future changes in climatic conditions. Given that most studies have focused on terrestrial species, here we contribute to this debate by analysing responses of marine native and non-native fauna and flora to key climate-related stressors, namely increased temperature (warming) and decreased salinity (freshening). Location: Global. Time period: 2002–2019. Major taxa studied: Marine benthic macrophytes and invertebrates. Methods: We conducted a meta-analysis of experiments investigating the performance (e.g. growth, survival and reproduction) of benthic species in response to warming and freshening. Results: We found that non-native species tended to respond positively to elevated temperature, whereas the performance of native species declined. Similarly, decreased salinity negatively affected the biological processes of native species, but non-natives showed neutral or negative overall responses to freshening. Main conclusions: We find evidence that non-native species outperform natives under a wide variety of warming and freshening conditions. The growth and reproduction of non-natives are enhanced by warmer temperatures, and thus ocean warming is expected to facilitate future spread and success of non-native species. Increased freshening along future coastal areas, however, will likely have a negative impact in both native and non-native species and thus is expected to be a driver of significant change in coastal marine ecosystems. Our comprehensive analysis highlighted the need to expand our understanding of climate change effects beyond warming and specifically, studies focusing on salinity changes.