Natures wonders: whale poop ecosystem (Introduction)

by David Turell , Thursday, November 04, 2021, 13:00 (1113 days ago) @ David Turell

Another important ecosystem is now understood:

https://www.sciencenews.org/article/baleen-whales-eat-poop-more-food-ecosystem?utm_sour...

"A new study finds that baleen whales, including blue and humpback whales, eat on average three times as much krill and other food as previously thought, and more food in means more poop out. Paradoxically, the collapse of the krill may stem from fewer whales excreting iron-rich, digested krill, denying these ecosystems some crucial nutrients they need to thrive. Phytoplankton blooms, which sustain krill and many other parts of the food web, rely on that iron. Restoring whale populations to prewhaling levels could help bolster these ecosystems and even store more carbon in the ocean, researchers report in the Nov. 4 Nature.

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"It turns out that, on average, baleen whales eat about three times as much food as earlier estimates suggested. For example, a blue whale can put down 16 metric tons of krill in a day, the researchers found. Energetically, that’s equivalent to around 10 million to 20 million calories, or about 30,000 Big Macs, Savoca says.

"Whales aren’t eating that much every day. The animals go for months without a bite when migrating vast distances. But the sheer volume of food that they consume, and then excrete, suggests that whales shape ocean ecosystems to a larger degree than previously thought, Savoca says, making their loss that much more impactful.

"That’s because one role whales play is that of nutrient cycler. By feeding on iron-rich krill in the deep and returning some of that iron to the surface in the form of poop, whales help keep this crucial element in the food web. Excessive whaling might have broken this iron cycle. With less iron at the surface, phytoplankton blooms shrink, krill numbers crash and the ecosystem becomes less productive, Savoca says.

"Before industrial whaling killed millions of whales in the 20th century, the researchers estimate that baleen whales in just the Southern Ocean alone, a key feeding area, consumed 430 million metric tons of krill each year, more than twice the biomass of all krill that’s found in those waters today (SN: 3/4/21). Even with today’s diminished populations, researchers estimate that whales prevent approximately 1,200 metric tons of iron from being lost each year, left to drift down to the dark deep of the Southern Ocean.

"Whales are likely not the only factor behind the staggering loss of krill, Savoca says, but the evidence suggests that “whales play a role here, and when you wholesale remove them, the system becomes, on average, less productive.”

"Some whale populations are rebounding (SN: 11/18/19). If whales and krill could be brought back to their early 1900s numbers, the productivity of the Southern Ocean could be boosted by 11 percent, the researchers calculate. That increased productivity would translate into more carbon-rich bodies, from krill to blue whales, which together would store 215 million metric tons of carbon annually, the equivalent of taking more than 170 million cars off the road for a year, the team suggests."

Comment: another example of the importance of top predators, and human damage to an ecosystem which is part of the huge necessary bush of life supplying food for all.