It's a good idea to apply sunscreen before heading to the beach if you don't want to burn and blister. But for marine animals like whales, that's not an option.
Species like sperm whales can spend up to six hours at the ocean's surface in between dives, baking in the sunlight. So how do they protect themselves from a serious case of sunburn?
It turns out that their bodies have similar defense mechanisms against the sun's ultraviolet (UV) radiation as people, according to a new study published August 30 in the journal Scientific Reports.
Researchers took more than a hundred skin biopsies from blue, fin, and sperm whales in the Gulf of California (map) from 2007 to 2009. They used crossbows loaded with modified arrowheads to retrieve plugs of skin from the marine mammals.
They found that blue whales—which have the lightest skin color of the three species—tanned during their summer sojourns before migrating back to their northern feeding grounds.
Sperm whales didn't tan. Instead, the whales, which can receive an "overdose" of UV radiation during their hours at the ocean's surface, have proteins that protect their cells from UV damage, said study co-author Mark Birch-Machin, a professor of molecular dermatology at Newcastle University in the United Kingdom.
And fin whales escaped sun damage thanks to their high levels of melanin—a skin pigment also shown to protect humans from UV radiation.
Studying how whales react to UV-radiation damage has never been done before, making the new paper very useful, said Marie-Francoise Van Bressem, a veterinarian specializing in skin diseases in whales, dolphins, and porpoises at the Peruvian Centre for Cetacean Research in Lima.
Now that the ozone layer that shields Earth from UV radiation is diminishing, "it's important to know what the consequences are for whales and dolphins, especially for vulnerable or endangered species," added Van Bressem, who was not involved in the study.
Instances of skin disease among whales, dolphins, and porpoises—collectively known as cetaceans—are on the rise, she said. And although it's difficult to tell what causes many of these skin conditions, UV damage is one cause.
Even though whales have built-in defenses to UV radiation, high exposure can still be harmful.
"At what point does that [skin lesion] develop into skin cancer?" asked Birch-Machin. No one knows, he said.
But it's important to figure out, he said, since the skin damage researchers are already seeing could serve as an early warning sign of a serious disease like cancer. (Learn about cancers in beluga whales.)
Birch-Machin and colleagues studied the DNA contained in the whales' mitochondria—a cellular organ responsible for powering the cell—in order to assess damage caused by UV radiation.
"Mitochondrial DNA damage is directly linked to UV exposure, which is why UV ages us," said Birch-Machin.
"Because the mitochondria are the battery packs of the cell, basically, our batteries run down."
The research team found that older whales, and whales with less melanin content in their skin—like blue whales—had the greatest level of damage in their mitochondrial DNA (mtDNA). Fin whales, which had the greatest amount of melanin, had the least amount of mtDNA damage.
Looking at the genetic consequences—or mtDNA damage—of UV radiation has also never been looked at in whales before, Birch-Machin said. And it turns out that this aspect of whale aging mirrors human aging. (Related: "Do Whales Have Culture? Humpbacks Pass on Behavior.")
Early Warning Signs?
Birch-Machin would like to figure out whether the skin blistering seen on these whales would develop into skin cancer.
He and his colleagues would also be interested in looking at other hairless marine mammals, such as walruses, to see if they have similar issues with UV-radiation exposure.
Although Birch-Machin does a lot of work on UV damage in human skin, he's excited about the prospect of delving further into other species.
"Whales will reflect the UV dose that the ocean receives," he said. As "floating dosimeters," they are a signal for the health of the ocean.
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