Impacts of the Predatory Whelk Mexacanthina Lugubris: A Dark Unicorn in Southern California Intertidal Communities

Climate-driven range shifts are well documented, but the impacts of range-shifting species on native communities are relatively unknown. In southern California, the dark unicorn whelk Mexacanthina lugubris has been shifting northward from its native range in Baja California, Mexico, which could lead to increased competition with endemic whelks and increased predation on shared prey species. To assess the effects of M. lugubris on local intertidal communities, we surveyed 10 Southern California sites over the course of a year to determine spatial overlap with native species and conducted feeding experiments to assess interactions with native whelks. Finally, thermal tolerance trials were run to predict how future climate change could alter population sizes and competitive ability. We found that M. lugubris was able to utilize space higher in the intertidal compared to local competitors and was often more abundant than native whelks in areas where establishment had more recently occurred. Additionally, M. lugubris had a greater impact on prey than native competitors and was able to tolerate higher temperatures. Understanding the potential for interactions with local species can help determine how expanding species may impact communities, and whether these impacts could increase under future warming.