Range expansion and establishment of a non-indigenous tunicate (Diplosoma listerianum)in thermal refugia is mediated by environmental variability in changing coastal environments

Abstract

Coastal marine non-indigenous species (NIS) have expanded their range into Atlantic Canada under more variable and anomalously warmer sea surface temperature (SST) conditions observed since 2012. In this study we apply species distribution modeling (SDM), in combination with empirical validation using annual field monitoring surveys, to assess the influence of anomalously warmer ocean conditions on the range expansion of NIS into coastal Nova Scotia using the recently established colonial tunicate Diplosoma listerianum as a test case. SDM accurately predicted D. listerianum’s introduction to Atlantic Canada, including its range expansion, contraction, and long-term persistence within thermal refugia as local environmental conditions generally warmed between 2012 and 2019. This tunicate’s ability to survive the winter was the primary constraint on its range expansion into Nova Scotia prior to 2012. The identification of local thermal refugia in which D. listerianum spread under anomalously warm winter conditions and persisted during colder winters provides new insights and a mechanism for range expansion and establishment of NIS. Ultimately, interannual modeling and long-term projections employed here can be applied to predict, monitor, and manage transient range expansion and long-term persistence of NIS within changing environments.