There are more than a thousand species of barnacles, mostly attached to rocks, reefs, and boats. A few species specialize in embedding themselves into the skin of whales, on which they grow and ride until they die. An individual whale may carry around up to 450 kilograms of barnacles and their shells, so permanently attached that the whale's skin grows around the bottom of the barnacle shells.
The problem in studying whale barnacles is that they tend to die when removed from the whale or from the ocean, so not much is known about their life cycles. All scientists have to work with are dead whale barnacles. However, other scientists study the composition of clam shells, which build up over time like tree rings, to analyze the composition of ocean water in the past. Biology professor Larry Taylor thought trying that with whale barnacles, who build their shells much faster than clams, might reveal not only information about the barnacles themselves, but could provide a roadmap for where its whale traveled. And we have dead whale barnacles that range from recent samples to fossils. By analyzing the isotopes in the layers of whale barnacle shells, we can trace the migrations of whales through history. This opens up a whole new world of information about how whales evolve, migrate, and go extinct, plus the state of the world's oceans over time. Those old barnacle shells are like an archive of ocean history for those who know how to analyze them. Read what whale barnacles can tell us at Hakai magazine. -via Metafilter