Last May, Vicky Barlow was exploring tide pools on a rocky beach in Cornwall, England, when she saw something colorful beneath a rock. It was a rainbow sea slug (Babakina anadoni). This marine creature normally lives along the southern coast of Europe—not in the more northern waters surrounding England.

This is the second sighting of a rainbow sea slug in England in the past two years. Scientists think that climate change is causing waters to warm, allowing some species—like sea slugs—to expand their range farther north. A change in temperatures can also cause ocean currents to shift, carrying unexpected creatures to different shores.