The oceans are huge carbon sinks for the world. Fish and whales comprise only a tiny part of their overall biomass. Nevertheless, studies have shown that fishing and whaling by humans have altered the ocean’s carbon storage and sequestration capabilities by causing a change in the food chain, or a trophic cascade. As naturalist and philosopher John Muir said, “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.”
That’s the bad news, though whale hunts seemed pretty good thinking in the days of whale-oil lamps, whalebone (“the plastic of the 1800s”), and decorative scrimshaw. The good news is that repopulation of the gentle giants could improve ocean carbon management without introducing non-native physical or chemical schemes or invoking bioengineering.
Sustainable Human has produced a wonderful video about how the trophic cascade works and how great whale activity supports sea life and naturally sequesters carbon dioxide, limiting climate change.
Good Nature Travel, the official travel blog of Natural Habitat Adventures and the WWF, describes how the process works:
“We know that the world’s forests—boreal, temperate, and tropical—play a large role in sequestering carbon dioxide (CO2)—as long as drought, harvesting, insect damage and wildfires don’t overpower them. But we may have another ‘champion’ helping us to combat rising CO2 levels: whales.
In what’s known as a trophic cascade (defined as an ecological process in which predators in a food web suppress the abundance or alter behavior of their prey, thereby releasing the next lower trophic level from predation or herbivory), whales help to sustain the entire ocean system. While they eat tons of fish and krill every year, whales actually help to keep them alive.”
The great whales have a meal plan that actually sustains their diet. They feed in deep, dark waters. When great whales surface, they expel in their iron- and nitrogen-rich feces nutrients that are scarce at the uppermost water levels. In the photic zone at the surface, the increased light causes photosynthesis, and the whale poop fertilizes the plant plankton that live up there. When the huge mammals leap and dive, their activity kicks the plankton around in the photic zone, giving it more time to reproduce. Plant plankton feeds animal plankton, which sustains larger creatures like fish and krill—the original diet of the whales!
Key to the climate effects: this plant plankton also absorb carbon dioxide, a potent greenhouse gas, from the atmosphere in large quantities. When the plankton eventually sink, they take the carbon dioxide down too, naturally sequestering it just as land vegetation does.
The science tells us that the huge whale population before the 1800s may have been removed tens of millions of tons of carbon from the atmosphere every year. As the video states, “The more whales there are, the more plankton there is. The more plankton there is, the more carbon is drawn out of the air.”
As Mother Jones puts it, “the incredible thing about whale poop is that it fights climate change.” Letting the great whale populations recover might help all of us by limiting the some of the anthropogenic damage caused by climate change. A paper in Frontiers in Ecology and the Environment last year nicknamed these ocean giants “marine ecosystem engineers.”