Petrel Bones Show How Humans Changed The Open Ocean Food Web

Pterodroma sanchwichensisIn one marine biology class I took long ago, the way we study the open ocean was compared to trying to study a forest by throwing a bucket out of a helicopter as you fly over and making conclusions based on whatever you happen to drag back up. Ocean exploration these days is a bit more sophisticated, but it’s still not easy, especially if someone wants to see how things have changed over the last several thousand years or so. But scientists figure out elegant solutions to these problems.

In a study published this week in PNAS, a research team led by the Smithsonian’s National Museum of Natural History investigated how the food web of the North Pacific Ocean has changed since humans began fishing there on a large scale by looking at the chemistry of petrel bones. Hawaiian petrels turn out to be a good proxy for what’s going on in the oceanic food web for several reasons: The birds breed only on the Hawaiian Islands, and their remains, dating back thousands of years, can be found in many archaeological and paleontological sites there. That makes the petrels special because most creatures that play a role in the oceanic food web die at sea. Even better, these bones contain a record, in the form of carbon and nitrogen isotopes, of where they foraged and what they ate when they were alive.

“Hawaiian petrels spend the majority of their lives foraging over vast expanses of open ocean,” lead author Anne Wiley of the Smithsonian Institution said in a statement. “In their search for food, they’ve done what scientists can only dream of. For thousands of years, they’ve captured a variety of fish, squid and crustaceans from a large portion of the North Pacific Ocean, and a record of their diet is preserved in their bones.”

Three decades of collecting 17,000 petrel bones have given these researchers a pretty good dataset to work with. And when they looked at the isotope information from the bones, the scientists found that from about 4,000 to 100 years ago, petrels were munching on bigger prey. But when humans intruded on the food web, snapping up the bigger fish, petrels changed their diet and gobbled up smaller creatures.

“Our bone record is alarming because it suggests that open-ocean food webs are changing on a large scale due to human influence,” coauthor Peggy Ostrom, a zoologist at Michigan State University, said in a statement.

It’s yet another case showing how humans are influencing the planet, and not necessarily for the better.

Image courtesy of Brittany Hance, Imaging Lab, Smithsonian Institution

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