Whalers have plucked giant whales from the sea for much of the last century, reducing their numbers by up to 99 percent for certain species. Some scientists thought that krill — the tiny crustaceans that many whales eat in gargantuan gulps — would explode in number as a result, mostly free from the feeding pressure of the largest animals that have ever lived.
But that didn’t happen. Instead, Antarctic krill numbers have dwindled since the mid-20th century, by more than 80 percent in areas heavily trafficked by whalers. Many other consumers of krill, like seabirds and fish, have suffered too in the absence of the crustaceans and their giant eaters.
Now, scientists have a clearer idea why this happened: whale poop, or rather, the lack of it.
A new study finds that baleen whales, including blue and humpback whales, eat on average three times as much krill and other food as previously thought, and more food in means more poop out. Paradoxically, the collapse of the krill may stem from fewer whales excreting iron-rich, digested krill, denying these ecosystems some crucial nutrients they need to thrive. Phytoplankton blooms, which sustain krill and many other parts of the food web, rely on that iron. Restoring whale populations to prewhaling levels could help bolster these ecosystems and even store more carbon in the ocean, researchers report in the Nov. 4 Nature.