科学美国人60秒:Whale Poop Drives Global Nutrient Cycling

The world's oceans were once home to 10 times as many whales… before the Captain Ahabs of the world came round. Hunting hit big species the hardest, wiping out 99 percent of the Southern Hemisphere's blue whales, for example. And as the gentle giants disappeared… so did another lesser known element of the oceans: their poop.

"I've described it as, sort of like oversteeped green tea. Like well steeped green tea. So it's very diffuse, in a big plume." Joe Roman, a conservation biologist at the University of Vermont. "My daughter's friends say I'm a whale poop scientist." And he says, he studies all kinds. "When whales are feeding on krill, they're really high lipids, lots of fat, so it sort of clumps together and floats at the surface. So there's a great variety of fecal plumes out there in the oceans."

Whale poop is important because it transports nutrients from the deep ocean, up to the surface. "Sperm whales feed on giant squid and other deep sea creatures. So they'll dive more than a kilometer down." Then they come to the surface to breathe, and digest, "and as it turns out they poop and they also pee. So they're releasing all these nutrients." Nutrients like phosphorous, which are slurped up by phytoplankton and algae. "Which is in turn is consumed by zooplankton, copepods or krill. And those are either eaten by fish or they can be eaten by seabirds."

Some fish swim up rivers and die; birds sprinkle the land with their guano; and those deep-sea nutrients slowly work their way into ecosystems on land with the help of bald eagles and bears and the like.

Roman and his colleagues modeled how that conveyer belt of nutrients has slowed due to the huge declines in whale, seabird and fish populations. And they reckon that only a quarter as much phosphorus makes it to surface waters today compared with the past. And the flow of phosphorus to land has nearly stopped--at just 4 percent of historic levels. The results are in the Proceedings of the National Academy of Sciences. [Christopher E. Doughty et al, Global nutrient transport in a world of giants]

Roman says this slowing of the nutrient conveyer belt is reversible, though. "The most important part for me is trying to restore these species as ecological engineers on the planet, and really try and share the planet with them. Let's not just keep them in zoos or even in small island pockets of protected areas. Let's let them move around the planet more freely." And when they do, he says… those key nutrients, too, will once again roam the Earth.

—Christopher Intagliata