The Planet Needs Whales

Whales play a vital role in the global nutrient cycle. The Proceedings of the National Academy of Sciences published a special issue in October about large mammals. One of the papers discussed “Global nutrient transport in a world of giants,” describing the oversized role that whales play in spreading nitrogen around for other ecological communities:

Despite their vastly decreased numbers, the important role of whales in distributing nutrients is just now coming to light.Whales transport nutrients laterally, in moving between feeding and breeding areas, and vertically, by transporting nutrients from nutrient-rich deep waters to surface waters via fecal plumes and urine. Studies in the Gulf of Maine show that cetaceans and other marine mammals deliver large amounts of N to the photic zone by feeding at or below the thermocline and then excreting urea and metabolic fecal N near the surface. [Emphasis added.]

The scientists estimate that whales transport almost four times as much nitrogen as terrestrial animals do. They also transport phosphorus and iron.

“Because of their enormous size and high mobility (and despite having many fewer species), great whales might have once transported nutrients away from concentration gradients more efficiently than terrestrial mammals,” the writers say. These nutrients are also “assimilated more rapidly, and contribute to system productivity more directly than on land.”

One of the diagrams in the paper, reproduced by Science Daily, shows the dependency of land animals on this nutrient cycle. Seabirds and “anadromous fish” like salmon carry these nutrients up rivers, where land animals like bears feed on the fish, profiting from the nutrients that whales had brought up from the deep ocean.

The authors even think that whales play a role in carbon dioxide levels that can affect the planet’s climate. They estimate that whale populations have been reduced by 90 percent from levels before the Moby Dick whaling days — raising alarms about ecological damage to planetary ecosystems. This interconnectedness of life raises fresh impetus to preserve these magnificent creatures.

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