Distributional changes in a guild of non-indigenous tunicates in the NW Atlantic under high-resolution climate projections

Predicting and understanding changes in coastal species distributions attributable to future climate change has become an increasingly important issue in ecology. We identify coastal areas in Atlantic Canada susceptible to future invasion by an important guild of epibenthic non-indigenous species (NIS) using ecological niche models calibrated with high-resolution climate scenarios. Specifically, we considered NIS in Atlantic Canada that are widely established (Botryllus schlosseri, Botrylloides violaceus, Ciona intestinalis, Styela clava) versus those that have recently been detected (Diplosoma listerianum, Ascidiella aspersa, Didemnum vexillum). Established NIS are predicted to be more strongly associated with colder temperatures and lower salinities than recently detected NIS. This helps to explain why, compared with recently detected NIS, established NIS are predicted to be more prevalent in Atlantic Canada currently and exhibit the greatest potential to expand their range under future climate scenarios. For example, the distribution of established NIS is predicted to shift northwards, while the area of suitable habitat is projected to more than double by 2075. The potential distribution of recently detected NIS is also predicted to shift northwards, with only a negligible increase in the area of potentially suitable habitat by 2075. These projected distributional changes may result in an expansion of areas where the distributions of recently detected and established NIS overlap to form NIS biodiversity hotspots. Our findings guide the development of pre-emptive and targeted NIS monitoring and mitigation strategies to guard against potentially negative impacts to bivalve aquaculture and sensitive ecological communities.