If you’ve never thought about how a whale’s poo affects you, the time is now.
Why? Because the faecal matter of whales, oversized land mammals, seabirds and migrating fish plays a critical role in fertilising the planet.
But a new study shows species decline and extinction is threatening the planet’s age-old ‘biogeochemical cycling’ system (or nutrient recycling system), potentially weakening ecosystem health, fisheries and agriculture.
“Previously, animals were not thought to play an important role in nutrient movement,” said Christopher Doughty, an ecologist at the University of Oxford and lead author of the study Global nutrient transport in a world of giants.
What the study highlights is the ability of animals to transport masses of nutrients in their faecal matter to ocean surface waters and inland, acting as a sort of nutrient “distribution pump.”
Published in the Proceedings of the National Academy of Sciences, the study was the result of a collaboration of scientists from the universities of Oxford, Vermont, Harvard, Aarhus (Denmark), Princeton, the Netherlands Institute of Ecology, and Purdue University.
They estimated that the capacity of animals to move nutrients away from concentration patches had dropped to around 8 per cent of what it once was, prior to the extinction of mammal megafauna at the end of the last ice age.
A key function of whales is to transport phosphorous, a key nutrient, from the ocean to the surface, however the study found their ability to do this has been reduced by more than 75 per cent.
“We propose that in the past, marine mammals, seabirds, anadromous fish, and terrestrial animals likely formed an interlinked system recycling nutrients from the ocean depths to the continental interiors,” the report said, “with marine mammals moving nutrients from the deep sea to surface waters, seabirds and anadromous fish moving nutrients from the ocean to land, and large animals moving nutrients away from hotspots into the continental interior.”
Traditionally, biogeochemistry suggests that “rock-derived” nutrients originate with the weathering or ageing of primary rock.
These nutrients are then lost to the hydrosphere by runoff or to the atmosphere by dust or fire, before they end up in the ocean, buried at the bottom of the sea.
“Eventually, these sediments are subducted, transformed to metamorphic or igneous rock, and uplifted to be weathered once again,” the report said. “We must wonder, what role do animals play in transporting nutrients laterally across ecosystem?”
According to the report, a significant one.
“Animal digestion accelerates cycling of nutrients from more recalcitrant forms in decomposing plant matter to more labile forms in excreta after (wild or domestic) herbivore consumption on land.”
In the present day it pointed to large herbivores enhancing nutrient cycling “in the grazing lawns of the Serengeti.”
The report concluded that the planet’s nutrient cycling system could be improved by more fenceless pastures with greater livestock biodiversity, management of commercial whale hunting to restore populations of the marine mammal and restoration of seabird colonies and anadromous fish populations.
“This once was a world that had 10 times more whales; 20 times more anadromous fish, like salmon; double the number of seabirds; and 10 times more large herbivores—giant sloths and mastodons and mammoths,” said Joe Roman, a whale expert at the University of Vermont and the Gund Institute for Ecological Economics.
“This study challenges the bottom-up bias that some scientists have that microbes are running the show, and phytoplankton and plants are all that matter.”
Read the article on The Age.