Climate change has driven contemporary decline and loss of kelp forests globally with an accompanying loss of their ecological and economic values. Kelp populations at equatorward-range edges are particularly vulnerable to climate change as these locations are undergoing warming at or beyond thermal tolerance thresholds. Concerningly, these range-edge populations may contain unique adaptive or evolutionary genetic diversity that is vulnerable to warming. We explore genetic diversity among extant and putatively extinct populations of the dominant kelp Ecklonia radiata in the south-western Pacific.
Six haplotypes occurred across the south-western Pacific with one being widespread across most populations. Three unique haplotypes were found in deep-water range-edge populations off Moreton Island, Queensland and are likely to represent historic refugia, protected by thermoclines. We also reveal that one of these unique haplotypes is most likely an ancestral lineage that crossed the equator into the south-western Pacific. The range edge, deep-water kelp populations off Moreton Island, represent an evolutionary refuge that is currently threatened by warming. Ex situ conservation efforts are warranted to protect this unique genetic diversity from extinction.