Integration of genetic connectivity and local adaptation in the design of marine protected area in the Southern Ocean: a case study opf Trematomus fishes

Polar ecosystems harbour a unique cold-adapted biodiversity that is threatened by rapid environmental change and increasing anthropogenic impact. In this context, multi-scale data on connectivity and adaptation are essential for supporting exploitation and conservation management of living resources and ecosystems. Notably, marine protected areas are most effective if implemented as a network that considers functional diversity and connectivity within and between species. In the present study, 607 individuals of ten Trematomus species were sequenced using ddRAD sequencing techniques. Thousands of genomic variants were used to investigate inter- and intraspecific patterns of divergence and connectivity across the Southern Ocean shelf. Moreover, genomic SNPs that showed evidence of selection (“outlier loci”) were used to explore potential local adaptation of the populations to different environmental conditions. Population structure analyses of four different species (T. loennbergii, T. eulepidotus, T. scotti and T. newnesi) suggest long- range dispersal across the Weddell Sea and even along the entire West Antarctic coast that might be facilitated by the Weddell Sea Gyre and Antarctic Coastal current. A genetic break at the level of the Filchner Trough was observed in several species. The strong outflow from the Filchner-Ronne ice shelf may separate the trough area from the remaining Weddell Sea habitat. Finally, results suggest that previously undetected cryptic diversity may be present within T. eulepidotus and T. loennbergii. Altogether, the present results contribute to the assessment of diversity, connectivity and adaptation on the Southern Ocean shelf, which is imperative in view of unprecedented global change.

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