The blue whale holds the title of the biggest animal on Earth, feeding primarily on vast amounts of tiny shrimp-like creatures called krill to maintain its enormous size, which can reach up to 100 feet (30 meters) long. Once abundant in the world’s oceans, blue whales and other baleen whales, which use their mouths to filter seawater for small marine organisms, faced severe population decline over the past century due to extensive hunting for their calorie-rich blubber.
As whale populations dwindled, some believed that krill would thrive without their natural predators. Contrary to this expectation, krill numbers also plummeted, and neither species has since recovered.
A new theory suggests that whales served a dual role in the oceanic ecosystem; their waste may have acted as a crucial fertilizer for marine life.
Research conducted by oceanographers from the University of Washington supports this idea, revealing that whale waste is rich in iron, a crucial element that is often lacking in ocean ecosystems, and safe forms of copper, another vital nutrient that can be harmful in certain forms.
This open-access study, which is the first to investigate the presence of these trace metals in what is commonly referred to as whale poop, appeared in January in Communications Earth & Environment.
“We made innovative measurements of whale feces to evaluate the significance of whales in recycling essential nutrients for phytoplankton,” said Patrick Monreal, a doctoral student in oceanography and the study’s first author. “Our findings indicate that the drastic decline of baleen whales due to historical whaling may have had extensive biogeochemical effects on the Southern Ocean, a region vital for global carbon cycling.”
The Southern Ocean, surrounding Antarctica and largely devoid of human presence, is crucial for the global climate. Powerful circumpolar currents push deep ocean water to the surface, fostering massive blooms of phytoplankton that support krill populations. These krill are still being harvested in unregulated waters for aquaculture and pet food today.
To explore the potential impact of whale feces on this ecosystem, the study evaluated five stool samples. Two were obtained from humpback whales in the Southern Ocean, and three from blue whales off California’s central coast. Researchers collected the samples opportunistically during their whale population studies.
“One advantage is that whale excrement floats,” noted Randie Bundy, a senior author and assistant professor of oceanography at UW. To collect it, researchers used a net attached to a jar to scoop up the material, which is usually in a slushy or slurry form.
“The theory is that whales add nutrients to the ecosystem, which are then utilized by phytoplankton, leading to their growth and subsequently feeding the krill,” Bundy explained.
Previous studies have identified considerable amounts of key nutrients such as nitrogen and carbon in whale feces. The current study took a different approach by investigating trace metals, which are often scarce in remote ocean areas and can limit the growth of marine life.
“Iron is regarded as one of the most limited nutrients necessary for phytoplankton survival in the Southern Ocean,” Bundy stated.
The findings confirmed the presence of iron in all samples, along with another metal, copper.
“We were quite surprised by the amount of copper found in the whale waste. Initially, we questioned whether the whale excrement might be toxic,” Bundy remarked.
However, further analysis revealed that organic molecules known as ligands were bound to the copper ions, changing them into a form that is safe for marine organisms. Other ligands facilitated the availability of iron to these organisms. The researchers are still investigating the source of these ligands but suspect that bacteria in the whales’ stomachs might be responsible.
Bundy’s research is centered on trace metals in marine environments. This project started as Monreal’s introductory research as a graduate student, but it expanded into a more comprehensive study as results were obtained.
“I believe that animals significantly influence chemical cycles more than many researchers acknowledge, particularly when considering ecosystem dynamics,” Monreal said. “By ‘animals,’ I mean their gut microbiomes. Evidence suggests that bacteria in whales’ intestines could play an important role.”
