Fossilized barnacles uncover ancient whale migration routes

Often considered one of the most boring and unremarkable organisms in the ocean, barnacles are now being used to track whale migrations over millions of years of evolutionary time.

Humpback
The migrations of humpback whales dating back thousands of years can be accurately tracked using their barnacles (photo by Tomas Kotouc via Shutterstock)

 

New research into the barnacles of whales has revealed these tiny hitchhikers can act like black boxes for whales, recording where in the world they have been and when. If that wasn’t impressive enough, the same study shows that even fossilized barnacles that are millions of years old can do the same thing. Migrations are believed to be an important factor in the evolution of baleen whales over the last 5 million years, as patches of productivity in the ocean started spreading out. This new window into the history of whales could also reveal how current populations are starting to be effected by climate change and noise pollution in today’s oceans.

Riding the whales

Almost all species of large baleen whales can be found with barnacles living on at least one part of their bodies. The tiny crustacean hitchhikers will spent their whole lives glued to a whale’s skin, being transported to some of the most nutrient rich waters in the world’s oceans free of charge. For many whale species the association with their encrusted counterparts is so strong that it would look eerily strange to see them without a healthy covering. Some researchers can even identify individual whale flukes based purely on the number and position of barnacles on them. Additionally each species of whale is believed to have their own unique species of personal barnacle that can’t be found on any other whale.

fluke ID
Individual humpback whales can be identified by the barnacle patterns on their flukes alone

Barnacle boxes

As well as filtering nutrients in the rich waters the whales seek out, the barnacles are also inadvertently absorbing something else as they are transported across the world. That something is oxygen isotopes. There are two isotopes of oxygen found in the oceans oxygen-16 and oxygen-18, with the ratio between the two being very specific to different regions based on temperature and salinity. Barnacles grow their shells by a few millimetres every month and so absorb oxygen isotopes into distinct calcium carbonate layers. Therefore by analysing the layers in barnacles researchers can determine exactly where they have been and when, much like how black boxes in cars and planes record different journeys in individual vehicles.

Gray whale barnacles
A patch of barnacles growing on the back of a gray whale

This technique was pioneered by PhD student Larry Taylor from the University of Calironia Berkley (UCB), whilst studying the barnacles of gray whales. He also discovered the same could be done with humpback barnacles and was highly accurate at tracking their extensive migrations, but the real breakthrough was when he discovered similar patterns in fossilized humpback barnacles he found in Panama. Larry then decided to team up with fellow researchers from UCB, as well as the Smithsonian Tropical Research Institute (STRI) to find out just how similar the barnacles of modern and ancient humpbacks and gray whales really were. Their findings were published last year in the journals PNAS.

Pre-historic GPS

The team looked at three locations in and around California and Panama where specimens of ancient whale barnacles, dating back to the Pleistocene, could be found. They carefully analysed the isotope levels in the shells and made some surprising discoveries. “The signals we found in the fossil barnacles showed us quite clearly that ancient humpback and grey whales were undertaking journeys very similar to those that these whales make today” said Taylor, talking to Science Daily last year, “it seems like the summer-breeding and winter-feeding migrations have been an integral part of the way of life of these whales for hundreds of thousands of years”. What’s more they also identified that Panama has been an important meeting ground for different subpopulations of humpback whales for at least 270,000 years. Individuals from Alaska and Antarctica continue to regularly visit the region today.

Fossilized barnacle
A fossilized humpback whale barnacle found in Panama (photo by Larry Taylor)

Tracking changes

These results were very interesting to whale researchers and showed us that the migratory pathways of whales can have deep evolutionary roots. However the study is more important because it was a successful proof of concept for this new research technique which could be used extensively in the future. “We want to push the technique further back in time and across different whale populations” said Seth Finnegan, co-author from UCB, who also explained “hunting for  whale barnacle fossils is easier than whales, and they provide a wealth of information waiting to be uncovered”. One way this type of research will help with conservation of cetacean groups is by highlighting any differences in past and present whale migrations caused by human impacts such as climate change and noise pollution.

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