The largest animals ever to have lived on Earth, blue whales are colossal in every respect – including, it must be said, the scatological. When a blue whale goes, it goes big.

This remarkable phenomenon was recently captured on camera by Eddie Kisfaludy, a marine biologist and oceanographic consultant. While conducting an aerial survey off the coast of southern California, he flew over a pod of 40 blue whales.

The waters were rich in krill, the tiny crustaceans on which blue whales feed, and their orange hue was brightly visible in a fecal plume he photographed. It's hard to judge absolute distances from the photo, but in scale the deposit is nearly as long as a full-grown blue whale.

It may well be the world's largest documented poop. It's also an exclamation point to a line of research pursued in recent years by marine biologists who say whales are the ocean's unappreciated gardeners, playing enormous roles in nutrient and carbon cycles. In short – or perhaps in long – their poop helps make the aquatic world go round.

"Whales and marine mammals can fertilize their surface waters," said Joe Roman, a conservation biologist at the University of Vermont, when shown Kisfaludy's picture. "This can result in more plankton, more fish, and more whales."

In 2010, after sampling the scat of humpback whales in the Gulf of Maine, Roman and Harvard zoologist James McCarthy proposed what they called the "whale pump": A mechanism describing how whales feeding at depth carry nitrogen to warm, energy-rich surface waters, discharging it in "flocculent fecal plumes."

Flocculent is a lovely word for a loose aggregation of particles, fluffy or woolly in nature. It's also why whale poop floats. Most previous research on oceanic carbon and nitrogen flows fixated on their downward drift, but the whale pump represented a flow in the opposite direction, a way for surface waters to continually be recharged, stimulating the growth of plankton and everything that eats them.

A schematic of the "whale pump." Image: Roman & McCarthy/PLoS One

Before commercial whaling, calculated Roman and McCarthy, the whale pump distributed three times more nitrogen across the Gulf of Maine than entered it from atmospheric sources. Even today, with whale populations at a fraction of historical levels, they added more nitrogen than all rivers and streams running into the Gulf combined.

Perhaps that's why sea life in the Gulf of Maine was once so abundant, and the benefits wouldn't have ended there.

As aquatic plants and animals grow, and in particular as plankton grows, they absorb carbon, then bury it on the seafloor when they die. That's the rationale behind iron fertilization, a geoengineering technique that some researchers think could counteract global warming.

From this perspective, whales aren't just gardeners, but geoengineers as well. Marine biologist Trish Lavery of Australia's Flinders University estimated that defecation by the Southern Ocean's sperm whales ultimately sequesters some 400,000 tons of carbon dioxide every year. Prior to their commercial whaling decline, that population alone would have accounted for about roughly the amount emitted by one decent-sized coal-fired power plant.

(Factor in the amount of carbon sequestered in whale bodies as they grow, calculated University of Maine marine biologist Andrew Pershing, and you can think about whale conservation in terms of carbon credits.)

An open and important question is how whale abundance alters ecosystems, Pershing said. Their effects could be enormous, especially when conceived in historical terms: Once there were more than 200,000 blue whales in the Antarctic Ocean alone, whereas today there are perhaps 8,000 in the whole world. Whatever they once provided has largely been lost, and restoring their populations might bring it back.

"Although other air-breathing vertebrates, such as seabirds and seals, can also pump nutrients to the surface, none are as large, or as abundant, as baleen whales were before the age of commercial whaling," said Roman. Blue whales' feces "must have a large impact on their ecosystems."

Asked what he thought when seeing Kisfaludy's photograph, Roman said, "I wish we had a net on hand to gather the poop."

Said Pershing, "I'm glad I don't have to pick that up."

Correction: The article originally stated that 400,000 tons of carbon dioxide was equivalent to the emissions of 400 coal-fired power plants. That is inaccurate. We apologize for the mistake.