Recolonization routes of intertidal species
Coalescent simulations showed that epifaunal species recolonized disturbed intertidal habitats from northern source populations (Table S3-S4). Specifically, for L. segnis , the best demographic model was recolonization from the North (AIC weight = 0.72). In O .neglectus the most supported model showed the uplift lineage has evolved through an admixture event between the Far and Nearby Northern lineages (AIC weight = 0.51). For the host species, the results from fastsimcoal simulations agreed with the previously published estimates of recolonization using approximate Bayesian computation (Parviziet al. 2020). Durvillaea poha is inferred to have recolonized the uplifted coasts via admixture between northern and southern source populations (AIC weight = 1) while in D. antarctica an admixture between the two northern source populations has resulted in the evolution of the uplift lineage (AIC weight = 0.77). For all four species, the recolonization events are estimated to have occurred approximately 900 years ago, in line with carbon-dating estimates of Akatore Fault rupture (Table S5).
Hierarchical-codemographic modelling using Multi-DICE supported a concerted post-earthquake recolonization (τ mode = 953 y BP; τ mean = 791 y BP; τ median = 825 y BP) with support for all intertidal and epibiotic species co-expanding within a 50 year period (Fig. 3). A more relaxed co-expansion threshold of 200 years also supported synchronous expansion of all four species which was estimated to have occurred 913 y BP (τ mode = 913 y BP; τ mean = 736 y BP; τ median = 747 y BP; Fig. S9-S10).