The Poop Loop
How whales fertilize the ocean and help counter climate change
The bowel movements of gentle giants set in motion a beautiful model for a circular economy. It goes like this: Whales poop, their poop feeds phytoplankton, which feeds krill… which feeds whales. There is a satisfying harmony to the miraculous marine poop loop — and we breathe, in part, because of it.
The oceans are by far the world’s largest heat and carbon sink. The Southern Ocean alone accounts for the sequestration of billions of tons of greenhouse gas emissions each year.
For this ecosystem service and more, we are indebted to phytoplankton, microscopic plant life at the ocean’s surface forming the base of the marine food web. Through photosynthesis, plankton remove carbon dioxide from the atmosphere and produce oxygen in exchange. More than two-thirds of the world’s oxygen is generated by ocean plants interacting with sunlight. But in order for this crucial photosynthesis to take place, a key ingredient is required: iron.
For bioavailable iron and other key nutrients, we can thank the pods of benevolent poopers.
Photo by Christian Miller
Whales, a mammalian group including the largest animals ever (blue whales), feed primarily on the smallest. They gorge on krill, tiny lobster-like crustaceans found most abundantly in cold waters like those of the Southern Ocean. Krill are also a big food source for penguins, seals, squid and fish (and anything that eats these species). They are iron-rich and crucial to the health and stability of the global marine ecosystem, as are the phytoplankton they eat, and the stinky poo clouds of their predators.
Post krill feast, a whale releases a plume of feces near the ocean’s surface with an iron concentration up to 10 million times higher than surrounding seawater. The iron acts as an electron carrier and a photosynthesis catalyst. If there’s enough iron and other nutrients (e.g. nitrogen and phosphorous), phytoplankton grow, photosynthesize and produce much of the oxygen in the air we breathe. They also sequester huge amounts of carbon.
As calcifying organisms, phytoplankton build their shells from calcium carbonate, which includes carbon. And then eventually they die, or get eaten. And when they do, they sink to bottom of the ocean, carrying that carbon with them. To recap: phytoplankton take up carbon, use it for their shells, and then remove it from the food chain and store it deep beneath the surface, in enormous quantities. This process is stimulated by the ‘waste’ materials whales return to the habitat that feeds them. Whales may help counter climate change simply by pooping in the oceans. It gets cooler.
Krill. Credit: NOAA NMFS SWFSC Antarctic Marine Living Resources (AMLR) Program
Like efficient recyclers and farmers, whales help circulate nutrients to make the oceans more productive — they nurture biodiversity in life and in death. Even the iron that sinks is returned to the loop with whales’ help. Sperm whales, for example, dive deep to feed on iron-rich squid. However, the pressure of the depths prevents defecation. They must return to the surface to breathe and expel their dung, thus creating a nutrient pump that boosts photosynthesis in the phytoplankton that sustain the krill, which in turn nourishes the whales, who farm the oceans… and so on and so forth in a cycle of give and take, and give... until our actions interfere.
Phytoplankton. Credit: NOAA MESA Project
Whales have lived and pooped in the world’s oceans for more than 50 million years. In the 20th century, humans, a much younger species, hunted them to the brink of extinction. Although we’ve yet to leave commercial whaling entirely in the past (ahem... Japan, Norway, Iceland), conservation efforts have helped many whale species rebound, only to face new threats in a world and climate drastically changed by humans.
Antarctic krill populations have declined more than 80% since the 1970s. Some point the finger at populations of whales rebounding after the 1986 IWC moratorium on their industrial slaughter. Others argue this theory overlooks the dire impacts of global warming, acidification, pollution, continued poaching and overfishing, and the phytoplankton-boosting benefits of iron in whale poop — a relatively recent discovery that threw yet another curveball in an emerging field of study.
Each scientific investigation delivers another dose of humility: we know shockingly little about life within the ancient ecosystem allowing for our survival. That hasn’t stopped us from altering it in the span of decades. Climate change, overfishing, deep-sea nets, noise and plastic pollution, and an appetite for exploitative resources like oil and krill supplements — these are the harpoons of the 21st century.
There are many layers to this story, and we are only just starting to uncover them. One thing is certain: this is crunch time for action to counter climate change and protect the ocean and its engineering species. In a world where whales wash ashore in the Amazon Rainforest and plastics pervade every known environment, we can’t afford to waste time and ignore uncomfortable truths. We need to get real about what matters most.
Ocean lovers, we implore you to go forth and fertilize the global consciousness by talking about whale poop. We gathered some talking points below.
10 things to know about whale poop
1. We breathe, in part, because whales poop in the oceans.
2. Whales are excellent recyclers, generous poopers and model contributors to a circular economy. Their feces release iron, which feeds phytoplankton, which feeds krill… which feeds whales.
3. A 2010 study found the concentration of iron in whale poop to be 10 million times higher than seawater concentrations.
4. In the Southern Ocean, iron defecation by sperm whales removes approximately 200,000 metric tons of carbon per year from the atmosphere, the equivalent of removing 70,000 vehicles that each travel 15,000 km per year.
5. Blue whales are the largest creatures ever known to have existed. They feed on one of the smallest. A blue whale consumes as many as 40 million krill in a day, the equivalent of about 8,000 pounds.
6. A whale is even generous in its afterlife. Its carcass ignites a deep-sea feeding frenzy and creates a new microbial community, returning vital nutrients to the ocean food chain.
7. The Parley SnotBot crew has declared whale poop samples at customs when traveling in the name of conservation science.
8. Fecal matter isn’t the only substance whales leave at the surface. Mucus emitted from a whale’s blowhole provides biological data about the health of whales and their habitat.
9. A rare type of sperm whale poop called ambergris is used in high-end perfumes (and sometimes cuisine). These waxy lumps of dung have reportedly netted $400,000.
10. Antarctic krill populations have declined more than 80% since the 1970s. When one species disappears, it affects the entire ecosystem. Antarctic krill play an especially vital role in supporting ocean life and mitigating climate change.
Header Image: © Jessica Luo / Cowen Lab / Plankton Portal
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