Like GPS trackers from the Pleistocene, barnacles that once hitched rides on the backs of humpback and gray whales record details of their ancient migrations more than 270,000 years ago.
Writing in the Proceedings of the National Academy of Sciences, researchers at the University of California, Berkeley have found that modern whales use similar migratory routes to their prehistoric relatives.
Barnacles are coin-sized crustaceans that literally stick to one place for their entire lives. Surrounded by a hard protective shell, the crustaceans stick out feather-like legs to capture passing microscopic organisms in the water as they hitch a ride from migrating whales in a relationship described as commensal.
Barnacles that attach to whales rather than stationary rocks or boats do so by boring into the whale’s skin. Throughout the course of their lives, barnacles grow up to a few millimeters each month by adding calcium carbonate from seawater to their shells. In doing so, the animals become indicators of ocean conditions at the time, recording details about the waters that whales migrate through. They retain this information even after they die, fall off, and fossilize, which allows scientists to follow the real-time migration of host whales from warmer breeding grounds in the South Pacific to colder feeding grounds in Alaska and the Arctic.
Barnacle clusters and the prints they leave help scientists to identify individual whales – different species of whale barnacles ride on different species of whales, allowing palaeontologists to pair fossilized barnacles with their previous host species. For at least 270,000 years, some populations of humpback whales have been meeting off the coast of Panama and, surprisingly, still do so today.
“One of the more exciting things about the paper, in my mind, is that we find evidence for migration in all of these ancient populations, from three different sites and time periods, but also from both humpback and gray whale lineages, indicating that these animals, which lived hundreds of thousands of years ago, were all undertaking migrations similar in extent to those of modern-day whales,” explained marine palaeontologist Larry Taylor in a statement.
This information allows researchers to understand how migratory patterns have impacted the evolution of whales over the last 3 to 5 million years, and how past adaptations to changing climates might help predict how modern whales will react to environmental changes today.
“We want to understand how malleable migratory behavior has been through time, how rapidly whales have adapted to previous climate changes, and see if this can give us some clues as to how they might respond to the current changes in Earth’s climate,” Taylor said. “How will whales cope with that, how will the food base shift, how will the whales themselves respond?”