Habitat Preferences at the Leading Edge of a Marine Bioinvasion

To enable the early detection and eradication of invasive species, it is crucial to predict habitats with an elevated risk of invasion. Despite the fact that invaders may display initial habitat preferences and niche shifts during range expansion, studies identifying habitat associations at invasion fronts are lacking, especially those considering abundance distributions. We developed a targeted Habitat Suitability Modeling approach to predict invasion risk, focusing on the Pacific oyster (<i>Magallana gigas</i>) invasion front on the Swedish southwest coast. We show that marinas act as environmental "hotspots" for pioneering non-native populations across broad spatial scales. The abundance observed in marinas (10.4 ind. m^-2) was higher than that in both piers (3.3 ind. m^-2) and natural rocky habitats (2.8 ind. m^-2). In terms of invasion risk, marinas were predicted to promote seven times higher oyster abundance and 20 times higher oyster biomass per unit area than natural rocky habitats. While the availability of stable hard substrate influenced presence, shelter from waves influenced abundance, demonstrating the ecological distinction between species occurrence and abundance distributions with important management implications. Moreover, supporting recent genetic findings, our model reveals an unexpected low-salinity tolerance at the invasion front, suggesting that range expansion may rather be limited by a lack of stable substrate. Our study provides novel insights into the dynamics of marine bioinvasions at leading range edges and offers a practical tool to inform early detection and proactive management of marine invasions, especially in commonly invaded anthropogenically structured habitats such as marinas.