Globally, species are undergoing range shifts in response to climate change. However, few studies have assessed the effects of range-shifting species as they establish in new communities, despite the potential for significant impacts. In southern California, the predatory whelk Mexacanthina lugubris has undergone a northward range shift of more than 100 km in the past four decades. Whelks are important intermediate predators in coastal marine ecosystems, and the introduction of a novel species could alter community structure through changes to existing species interactions. We traced the history of the whelk’s range shift and assessed potential impacts on native species using an integrated approach, consisting of field surveys, as well as feeding and thermotolerance experiments. We compared tide height distributions (presence and absence) of native whelks at sites with and without Mexacanthina using gamma hurdle models. Feeding experiments were analyzed with a two-way interactive ANOVA to assess the effects of predator and prey compositions, and a logistical regression was used to calculate LT50 and quantify differences in survival by species and temperature.
Results/Conclusions
We found Mexacanthina has continued to expand northward. At sites where Mexacanthina occurred, native whelk presence was affected by Mexacanthina presence (p< 0.001), tide height (p< 0.001), and their interaction (p=0.002) with native whelks occurring more often lower in the intertidal. The same pattern was true as Mexacanthina density increased (p< 0.001). Native whelk densities also peaked lower in the intertidal due to an interactive effect of tide height and Mexacanthina presence (p=0.02) and density (p=0.04). In laboratory experiments, we found that the presence of Mexacanthina, but not conspecifics, led to reduced growth in the native whelk Acanthinucella spirata (p< 0.001). There was no effect of prey composition or the interaction with predator composition. Additionally, the range-shifting whelk showed similar thermal tolerance as the native Acanthinucella, but was able to tolerate higher temperatures than Nucella emarginata (p=0.02). This suggests further impacts as a result of climate warming as many species are likely to undergo range shifts as a coping mechanism for changing climatic conditions, but communities are unlikely to shift as a whole due to species-specific responses. By studying the impacts of range-shifting species, like Mexacanthina, we can better understand how climate change will alter existing community structure and composition.
