Trace Metals and Other Nutrients from Whale Feces Fertilized Ancient Oceans, New Study Confirms | Sci.News

Blue whales and other baleen whales, which filter seawater through their mouths to feed on small marine life, once teemed in Earth’s oceans. In the 20th century, 1.5 million baleen whales were slaughtered in the southern hemisphere, including over 95% of the largest species — fin (Balaenoptera physalus) and blue whales (Balaenoptera musculus). Contrary to expectations, krill biomass on the former whaling grounds declined sharply (over 80%) in the decades following whaling, particularly in the Southern Ocean. A recent theory proposes that whales weren’t just predators in the ocean environment. Nutrients that whales excreted may have provided a key fertilizer to these marine ecosystems. New research led by the University of Washington supports that theory. It finds that whale excrements contain significant amounts of iron, a vital element that is often scarce in ocean ecosystems, as well as non-toxic forms of copper, another essential nutrient that in some forms can harm life.

“We made novel measurements of whale feces to assess how important whales are to recycling important nutrients for phytoplankton,” said Patrick Monreal, a doctoral student at the University of Washington.

“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.”

The Southern Ocean encircling Antarctica harbors little human life but is thought to play an important role in the global climate.

Strong circumpolar currents bring deep ocean water up to the surface.

Huge blooms of plant-like organisms known as phytoplankton support populations of krill, which are still harvested in unprotected waters today for aquaculture and pet food.

To investigate what role whale excrements may have played in this ecosystem, Monreal and his colleagues analyzed five baleen whale fecal samples.

Two samples were from humpback whales in the Southern Ocean and three were from blue whales off the central Californian coast.

“The nice thing, I guess, is that whale excrement floats,” said Dr. Randie Bundy, a researcher at the University of Washington.

“Researchers collect it using a net attached to a jar to collect the substance typically found as a slushy or slurry material.”

“The hypothesis is that the whales were actually adding nutrients to the ecosystem that these phytoplankton were able to use, so they would bloom more and then the krill could eat them.”

Previous research had found significant amounts of major nutrients, like nitrogen and carbon, in whale excrement samples.

The new study instead looked for metals that are in short supply far from land and are often a limiting factor for the growth of ocean ecosystems.

“In the Southern Ocean, iron is considered to be one of the most scarce, or limiting, nutrients that phytoplankton need to survive,” Dr. Bundy said

Iron was present in all the samples. The researchers also found another metal, copper.

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

“Further analysis showed that organic molecules known as ligands attached to the copper atoms transformed them into a form that is safe for marine life.”

“Other ligands helped make the iron accessible to living organisms.”

“We don’t yet know the source of the ligands but suspect they may come from bacteria in the whales’ stomachs.”

The results were published January 10 in the journal Communications Earth & Environment.

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P.J. Monreal et al. 2025. Organic ligands in whale excrement support iron availability and reduce copper toxicity to the surface ocean. Commun Earth Environ 6, 20; doi: 10.1038/s43247-024-01965-9