Population genomics data for the temperate seagrass Posidonia sinuosa

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Seagrasses are flowering plants commonly found along coastal waters, globally, where they provide important ecosystem services such as habitat provision, sequestering carbon, and sediment stabilization. They can reproduce both clonally and sexually where sexual reproduction can result in new, potentially adaptive, variants and the existence of both reproductive methods means that meadows can be highly variable in clonal diversity. The temperate seagrass, Posidonia sinuosa, occurs across a latitudinal gradient along the Western Australian coastline. Some meadows have experienced significant decline as a result of industrialisation and urbanisation of coastal areas. We investigated spatial genetic diversity, structure, and local adaptation using genomic markers through ddRAD-seq. Thirty Posidonia sinuosa meadows were sampled across its latitudinal range on the west coast of Australia between Geraldton and Geographe Bay. Sites were selected to cover a temperature and depth range and where long-term monitoring of seagrass condition has occurred. The data set contains 7,777 SNPS for 287 individuals across 28 seagrass meadows after bioinformatic filtering. All meadows had similarly low levels of genetic diversity, with high levels of inbreeding. Weak genetic structure across the latitudinal gradient was consistent with genetic connectivity, enabled by sea-surface seed dispersal. Approximately 6.1% of markers were identified as putatively adaptive and most were associated with temperature variables. Allelic turnover was associated with a < 1.4 C temperature change, suggesting plants may be sensitive to small temperature changes. Meadows are currently growing in temperatures below their thermal optima, suggesting they may be able to tolerate future projected temperatures up to a point. They are unlikely to tolerate current projections for 2100, which equate to +3.2 C, in addition to extreme heatwave events. Conservation of fragmented, northern, warmer-adapted meadows will be important to assist recovery and persistence of damaged meadows into the future, as translocation of putatively warmer-adapted genotypes between meadows that have exhibited historic connectivity may be a viable strategy for restoration of impacted higher latitude meadows.