Whale poop is a natural fertilizer that keeps the ocean alive

Blue whales, the largest creatures on Earth, have long captivated scientists and the public alike. Reaching lengths of up to 100 feet (30 meters), these immense mammals depend on huge quantities of krill – tiny, shrimp-like crustaceans – to sustain their colossal bodies. 

Historically, blue whales, along with other baleen whales, roamed the oceans in great numbers, filtering seawater for small marine life. However, the past century brought intensive commercial whaling that nearly eradicated them. 

Intriguingly, krill populations also plummeted instead of thriving in predator-free waters, and neither species has fully rebounded. This paradox has prompted scientists to investigate whales’ larger role in marine ecosystems.

Whales as nutrient recyclers 

A new study from University of Washington (UW) oceanographers offers insight into this mystery. The research suggests that whales may act not just as top predators but also as crucial nutrient recyclers, fertilizing the open ocean through their excrement. 

By providing essential trace metals like iron and non-toxic forms of copper, whales may bolster phytoplankton productivity, thereby sustaining the food web from the bottom up.

“We made novel measurements of whale feces to assess how important whales are to recycling important nutrients for phytoplankton,” said first author Patrick Monreal, a UW doctoral student in oceanography. 

“Our analysis suggests that the decimation of baleen whale populations from historical whaling could have had larger biogeochemical implications for the Southern Ocean, an area crucially important to global carbon cycling.”

Whale poop and a nutrient puzzle 

For decades, scientists assumed that if whale numbers fell, then their primary prey – krill – would flourish in predator-free waters. Instead, krill populations declined as well. This conundrum spurred the idea that whales might be more than mere consumers, potentially playing a vital role in fertilizing the waters they inhabit. 

In particular, the Southern Ocean surrounding Antarctica, with its strong currents and nutrient-rich upwelling, is recognized as a key player in climate regulation. 

Despite the nutrient content in deep water, essential elements such as iron can be in short supply at the surface, limiting phytoplankton growth. Without abundant phytoplankton, krill lack the food needed to sustain their populations.

Understanding this dynamic is crucial because phytoplankton, akin to terrestrial plants, form the foundation of marine food webs. They convert sunlight and carbon dioxide into organic matter, sequestering carbon and fueling the entire oceanic community. 

If whale waste – rich in iron and other trace metals – once stimulated massive phytoplankton blooms, the decimation of whales could have curtailed this nutrient supply. This may have contributed to declines in krill and reshaped oceanic ecosystems in ways still felt today.

Gathering and analyzing whale waste

To investigate whales’ nutrient contribution, researchers collected five fecal samples: two from humpback whales in the Southern Ocean and three from blue whales off central California. 

Although securing such samples might sound challenging, opportunistic collection is possible when whales defecate at the surface – whale excrement floats, forming a distinctive cloud that can be scooped up with a small net.

“The nice thing, I guess, is that whale excrement floats,” said senior author Randie Bundy, an assistant professor of oceanography at UW.

Previously, scientists had documented high levels of nitrogen and carbon in whale poop, but the new study focused on trace metals, substances often lacking far from land but essential for phytoplankton growth. 

The team analyzed the whale feces for iron, known to be especially limited in the Southern Ocean, as well as copper.

Iron, copper, and the microbial connection

All five samples showed substantial iron content, reinforcing the hypothesis that whale waste functions as a fertilizer in nutrient-poor waters. The presence of copper astonished the researchers.

“We were really shocked by how much copper was in the whale poop. We initially thought, ‘Oh, no, is the whale poop actually toxic?’” Bundy said.

A deeper analysis indicated that the copper atoms were bound to organic ligands, molecules that render copper safe and bioavailable for marine life. These ligands also appear to help phytoplankton access iron more effectively. 

The scientists suspect that gut microbes living within the whales may generate these ligands, acting as microscopic chemists that transform the animals’ feces into a highly beneficial nutrient source.

“I think animals play a larger role in chemical cycles than many experts give them credit for, especially when thinking at the ecosystem scale,” Monreal said. “When I say animals, I really mean their gut microbiome. Based on what we see, it seems like bacteria in the whales’ guts could be important.”

Implications for conservation and climate

The Southern Ocean is a critical zone for global carbon cycling, making these findings especially significant. If whales once substantially fertilized these waters, their near-eradication may have altered entire food chains. 

As whale populations slowly recover, it’s possible their nutrient recycling activity – sometimes termed the “whale pump” – could also rebound, bolstering phytoplankton and helping reestablish robust marine communities.

Moreover, given that phytoplankton sequester carbon dioxide, a fuller understanding of whales’ role in promoting these blooms may inform climate mitigation efforts. 

By illuminating the profound but underappreciated role of whale poop, this study underscores how preserving and restoring whale populations could ripple through oceanic ecosystems, affecting biodiversity, fisheries, and even carbon storage.

Ultimately, the research illustrates that whales, far from being mere consumers, actively shape their habitats. Their excrement stands as a striking example of how interconnected life in the ocean truly is – a reminder that conserving key species often helps uphold the entire, intricately balanced system beneath the waves.

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