Climate-assisted persistence of tropical fish vagrants in temperate marine ecosystems

Rising temperatures and extreme climatic events are propelling tropical
species into temperate marine ecosystems, but not all species can persist.
Here, we used the heatwave-driven expatriation of tropical black
rabbitfish (Siganus fuscescens) to the temperate environments of Western
Australia to assess the ecological and evolutionary mechanisms that may
entail their persistence. Population genomic assays for this rabbitfish
indicated little genetic differentiation between tropical residents and
vagrants to temperate environments due to high migration rates, which were
likely enhanced by the marine heatwave. DNA metabarcoding revealed a
diverse diet for this species based on phytoplankton and algae, as well as
an ability to feed on regional resources, including kelps. Irrespective of
future climate scenarios, these macroalgae-consuming vagrants may
self-recruit in temperate environments and further expand their geographic
range by 2100. This expansion may compromise the health of the kelp
forests that form Australia’s Great Southern Reef. Overall, our study
demonstrates that projected favourable climatic conditions, continued
large-scale genetic connectivity between populations, and diet versatility
are key for tropical range-shifting fish to establish in temperate
ecosystems.