Genomic analyses and climate models reveal a rapid but long-lasting climate-driven geographic expansion of a tropical herbivorous reef fish

Dr Laura Gajdzik^1,2, Dr Thomas DeCarlo³, Mr Adam Koziol¹, Dr Mahsa Mousavi-Derazmahalleh¹, Prof Michael Bunce¹, Dr. Joseph DiBattista^1,4

¹Curtin University, Bentley, Australia, ²King Abdullah University of Science and Technology, Thuwal, Saudi Arabia, ³The University of Western Australia, Crawley, Australia, ⁴The Australian Museum Research Institute, Sydney, Australia

A timely question in ecology is to determine the impacts of climate change on species’ distribution. As the ocean warms, fish species extend their range poleward causing a tropicalisation of marine temperate ecosystems worldwide. Range-shifting herbivorous fish can alter the function of habitat-forming seaweeds by removing the adult thalli, impeding their re-establishment, and increasing competition. Here, we investigated the tropicalisation of marine temperate environments in Western Australia by focussing on the tropical herbivorous rabbitfish Siganus fuscescens that migrated poleward following a marine heatwave in 2010-2011. We combined genomic tools with climate models to better understand the population dynamics of this range-shifting fish species, compare the diet between resident tropical individuals and migrants to temperate reefs, and predict how far and for how long migrants will establish in new environments by the end of this century. Our results, based on 5,507 single nucleotide polymorphism loci, revealed an absence of genetic differentiation among all rabbitfish individuals sampled across 2,500 km of tropical to temperate environments. Using DNA metabarcoding, we found that the diet composition differed between tropical individuals and temperate migrants, with a prevalence of locally-produced macroalgal species. Past and present observations, as well as forecasting of two biologically-meaningful temperature contours, suggest that S. fuscescens will overwinter, survive, and likely reproduce in temperate environments up to 1,400 km away from its present-day distribution along the west coast of Australia. Together, these findings demonstrate a rapid, long-term, and climate-driven expansion of a highly adaptable species’ population with drastic consequences for marine temperate ecosystems.

Biography:

Dr. Laura Gajdzik is a marine biologist who primarily studies the ecology of reef fishes with a multidisciplinary approach combining trophic ecology and functional diversity with genomic and phylogenetic comparative methods. Laura worked in the TrEnD Lab at Curtin University (Australia) on the tropicalisation of marine temperate environments in Western Australia using genomic tools and climate models. She is now a research postdoctoral fellow in the Reef Ecology Lab at the King Abdullah University of Science and Technology (Saudi Arabia) investigating the resilience of coral and fish communities in the Red Sea.