Barnacles stuck to ancient whales kept an itinerary of whale migration routes
Barnacle shells preserved a chemical signature of the journeys whales took
Migration is an integral part of whale ecology. Many whales spend summers feeding in cold waters, then move to warmer tropical waters to breed. The demands of long distance migration has played a key role in shaping the evolutionary history of whales, but until recently, little was known about the patterns of ancient whale migrations.
To understand more about those patterns, scientists from the Smithsonian Tropical Research Institute and the University of California Berkeley - including Integrative Biology doctoral student Larry Taylor - came up with a very clever approach. They simply went to the hitch-hiking passengers on those ancient whale migrations - barnacles - and 'downloaded' the story.
Whales and their hitch-hiking barnacle companions
Barnacles are best known as sessile creatures that stick to rocks or perhaps ships. But some species of barnacles glue themselves to whales. They create a tight bond to the whale by drawing part of the whale's skin into hollows in their shells. They then ride along on the long migrations whales make for food, mating, and reproduction.
The benefit for the barnacles is that the whales migrate to some of the most nutrient rich waters in the world, where the barnacles, like the whales, can filter food from the water.
Fossil barnacles as time tracking devices
Taylor came up with the idea to look at fossil barnacles to see if they could reveal anything about whale migration looking back hundreds of thousands or even millions of years.
The idea was inspired by the fact that the calcite plates that make up barnacle shells grow by depositing new material at the base. This leaves 'tree-ring' like growth layers that preserve a chemical and temperature signature of the waters in which the barnacles are growing.
These signals in the shells can tell researchers today which bodies of water a whale has passed through.
Taylor's insight was that this information could be teased out from fossil whale barnacles from past eras. Taylor and his colleagues concluded that the ancestors of modern humpbacks and grey hwales were making similar migration journeys hundreds of thousands of years ago, as they do today.
Not such a weird idea after all
Taylor admits that when he first proposed this idea his research supervisor was skeptical. It was a weird and risky idea that likely would come to nothing. But in fact it worked remarkably well.
In the future the researchers want to push the idea further back in time and across other populations of whales.