Should we be worried about a loss of whale poo?

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A recent study by the University of Oxford has revealed that declines in whales, fish, seabirds and large land mammals are disrupting the Earth’s nutrient cycle.

In the past, marine mammals, sea birds, anadromous fish and terrestrial animals formed an interlinked system that recycled nutrients in their faecal matter from the deep water to the continental interiors. This involved marine mammals transporting nutrients from the ocean depths to the surface waters, seabirds and anadromous fish moving the nutrients from the ocean to the land and then large terrestrial animals transporting nutrients away from these hotspots into the continental interior. In other words their faeces fertilise areas that otherwise would not receive nutrients.

The paper, published in the Proceedings of the National Academy of Sciences, revealed that this animal-powered planetary pump has reduced to a meagre 6 percent of its former capacity, due to many of the largest animals becoming extinct or experiencing huge population declines.

Whale numbers, for example, have been estimated as dropping between 66% and 90% over the past three centuries, mainly as a result of commercial hunting. Whales play a role in transporting phosphorus from concentrated hotspots to other ocean areas by feeding in the depths and then defecating at the surface. Their faecal matter has the power to greatly influence the ecosystems of our planet by enhancing primary productivity to support other large animals. They therefore play an important component in keeping our planet fertile. Before commercial whaling, the ocean giants moved approximately 750 million pounds of phosphorus from deep waters to the surface. This figure is now staggeringly low in comparison, being only 165 million pounds. That is just 23 percent of their previous contribution. Not only do declines in global whale population densities result in a fall in nutrient transport, but fewer whales could also mean fewer phytoplankton at the ocean surface, which could cause cascading effects across ecological communities.

However, it is not just populations of whales that are falling and effectively disrupting the efficient nutrient distribution pump. Decimation of seabird colonies and anadromous fish populations have resulted in 96 percent less phosphorus being transferred from the sea to the land, according to the study.

In the past, the abundance of large free-ranging animals enabled nutrients to be more evenly distributed and account for global fertility. This study challenges the bottom-up theory that some scientists possess and highlights how it’s not necessarily all about the microbes and primary producers. Large animals also partly control the nutrient supply, productivity and range of primary producers that shape the ecosystem structure.

A planet deprived of large animals, be it whales, salmon or seabirds is a less productive one and can potentially weaken ecosystem health, fisheries and agriculture. Recovery of the nutrient cycle is possible if we restore populations of large vertebrates.

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Lucy Grable

Lucy Grable

MSc Species Identification and Survey Skills student at Reading Uni | BSc Marine Zoology | Website Editor MARINElife | Zanzibar humpback whale researcher|Marine wildlife enthusiast

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