Scientists have discovered kelp off the coast of Ireland that has survived since the last Ice Age around 16,000 years ago.
Experts from Heriot-Watt University's Orkney campus, the University of the Algarve in Portugal and Station Biologique de Roscoff in France analysed the genetic composition of oarweed from 14 areas across the northern Atlantic Ocean.
Three distinct genetic clusters were found - one along the eastern seaboard of Canada and the US, one in central and northern Europe and a compact population around Brittany.
Dr Andrew Want, a marine ecologist at Heriot-Watt's International Centre for Island Technology in Orkney, described the finds as "refugee populations that managed to hang on and survive amid dramatic changes as ice sheets retreated".
Dr Want said: "Oarweed in Scotland and Ireland is more closely related to populations in the high Arctic than to the Brittany cluster. As the ice sheets retreated from northern European shorelines at the end of the most recent Ice Age, oarweed distribution followed and recolonised the higher latitudes of the Atlantic.
"Kelp plays a critical role in the Atlantic so it is important to understand what affects its distribution and survival over time and how sensitive it is to change."
It is hoped the discovery of how closely related the populations are - published in the 'European Journal of Phycology' - can help solve how marine plant life survives climate change.
Dr Joao Neiva, from Algarve's Centre of Marine Sciences, said: "Our study shows how marine organisms adjust to shifting climates by migrating polewards and even across the Atlantic when conditions are favourable.
"These migrations provide a mechanism by which marine life buffers the effects of global climatic shifts, and how they can compensate for predictable contractions at warmer limits as the modern climatic crisis unfolds.
"While the species may not be threatened at global scales, range contractions can have very negative impacts if vanishing ranges are composed of unique and diverse populations. This is certainly the case off the coast of Brittany."