Study: Vanishing hippos are critical to African ecosystem health
The hippopotamus is contributing to ecosystem health in African lakes and rivers in a way that scientists haven’t considered before, and it’s because of the beneficial silicon that hippos are transferring through their poop.
“Hippos differ from other large grazing animals in the savannah,” said biologist Jonas Schoelynck from the University of Antwerp, lead author of a new study published in the journal Science Advances.
“The nutrients in the excrements of most grazers largely end up back in the savannah again, where they are reabsorbed by the plants,” Schoelynck said. “This is not the case with hippos: they act as a kind of nutrient pump from the land to rivers and lakes.”
Wild hippos eat massive amounts of grass at night, but they spend their days keeping cool and staying wet in lakes and rivers. Much of the poop they eliminate goes into those waters, including the 400-kilometer long Mara River in the Masaai Mara Nature Reserve in Kenya. It’s there that Schoelynck, Patrick Frings from the German Research Centre for Geosciences GFZ and the research team studied the hippo herds.
Through various pathways, the hippo-silicon contribution influences more than 76 percent of the total silicon transported along the Mara River. That’s critical to the ecosystem, including oxygen-producing algae that serve as a foundation for the entire food chain in a river that flows into Lake Victoria.
“Lake Victoria, into which the Mara River flows, can survive for several decades with its current silicon supply,” Schoelynck said. “But in the long run there is probably going to be a problem.”
The rapid loss of hippos in recent years – up to 90 percent in Africa are now extinct – is because of habitat loss and hunting, and that has implications for the intricate food web and the interplay between land and water. Ultimately, human food supply is threatened because fish stocks are depleted when the silicon is unavailable to the beneficial algae, leading to lower oxygen levels and setting the negative consequences in motion.
Image: Jonas Schoelynck