Nav: Home

Hippos, the animal silicon pumps

May 01, 2019

The excrements of hippos play an important role in the ecosystem of African lakes and rivers. Because there are fewer and fewer hippos, this ecosystem is in danger. In the long term, this could lead to food shortages at Lake Victoria, for example. These are some of the results of a new study by an international team of researchers published in the journal Science Advances. Patrick Frings from the German Research Centre for Geosciences GFZ is part of the research team behind it.

Wild hippos have a unique lifestyle: at night they eat dozens of kilograms of fresh grass in the savannahs. Most of their days they spend relaxing together in rivers or lakes, far away from enemies and protected from the burning sun. While chilling in the water, however, their digestion becomes active. Thus, enormous quantities of hippo poo enter the water.

"Hippos differ from other large grazing animals in the savannah," explains biologist Jonas Schoelynck from the University of Antwerp, the first author of the study. "The nutrients in the excrements of most grazers largely end up back in the savannah again, where they are reabsorbed by the plants. This is not the case with hippos: they act as a kind of nutrient pump from the land to rivers and lakes." In the study now published, researchers around Schoelynck and Frings show that this pumping function can be crucial for life in water. The results come from an expedition to the nearly four hundred kilometre long Mara River in the Masaai Mara Nature Reserve in Kenya.

Hippo excrements examined in the lab

"The grass that hippos eat contains silicon," explains Jonas Schoelynck. "The grass absorbs this silicon from the groundwater. It gives it the strength it needs, protects it from disease and, to a limited extent, from grazing by small animals". Patrick Frings from the Geochemistry of the Earth's Surface Section of the GFZ analysed the isotopic composition of silicon in samples of plants, water and hippo excrements in the laboratory. This type of analysis provides a kind of chemical fingerprint of a sample substance. "The isotope analysis enabled us to reconstruct the transport path of the silicon," explains Frings.

The researchers showed that a large part of the silicon in the Mara River was transported there via hippos. In the investigated area in southwest Kenya, the grazing animals absorbed a total of 800 kilograms of silicon per day through the plants they ate. 400 kilograms per day ended up in the water via excretion of hippo faeces. Through various ecological mechanisms, the hippos' silicon contribution influences over 76 percent of the total silicon transported along the Mara River, according to calculations by the researchers. Hippos are therefore a key factor in the biogeochemical silicon cycle of certain areas.

"Our results are completely new," says Patrick Frings of the GFZ. "So far, it has not been assumed that grazing wild animals could have such an influence on the transport of silicon from land to lakes. This process is crucial for the entire land-water ecosystem. In the past, however, it has simply been overlooked."

A world without hippos

According to the researchers, silicon is vital for certain organisms such as diatoms. These unicellular algae live in the water, produce oxygen and form the basis of the food chain in many water ecosystems. If a lack of silicon occurs, the diatomaceous algae population can collapse, with harmful consequences for the entire food web in the lake or river concerned, the researchers say.

The number of hippos in Africa has been drastically reduced in recent years due to hunting and loss of habitats and their function as animal silicon pumps has thus been partially lost, say the researchers. In recent decades, up to ninety percent of hippos in Africa have become extinct. "Lake Victoria, into which the Mara River flows, can survive for several decades with its current silicon supply," says Jonas Schoelynck. "But in the long run there is probably going to be a problem. If the diatoms do not get enough silicon, they are replaced by pest algae, which have all sorts of unpleasant consequences, such as a lack of oxygen and the associated death of fish. And fishing is an important source of food for the people of Lake Victoria.
Original study: Schoelynck, J., Subalusky, A.L., Struyf, E., Dutton, C.L., Unzué-Belmonte, D., Van de Vijver, B., Post, D.M., Rosi, E.J., Meire, P., Frings, P., 2019. Hippos (Hippopotamus amphibius): The animal silicon pump. Science Advances. DOI: 10.1126/sciadv.aav0395

GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre

Related Ecosystem Articles:

Diversity increases ecosystem stability
Freiburg's forestry scientists prove that forests that are more diverse are also more productive and more resilient
From the tropics to the boreal, temperature drives ecosystem functioning
University of Arizona researchers found a tight link between temperature and plant and microbe communities within forests, which will allow them to predict how ecosystems might respond to climate changes.
Indigenous knowledge, key to a successful ecosystem restoration
Ecological restoration projects actively involving indigenous peoples and local communities are more successful.
Ecosystem responses to dam removal complex, but predictable
In the United States, the removal of dams now outpaces the construction of new ones -- with more than 1,400 dams decommissioned since the 1970s -- and a new study suggests that the ecosystem effects of dam removal can be predicted.
How one gene in a tiny fish may alter an aquatic ecosystem
Variations in a single gene in a tiny fish alter how they interact with their environment, according to research led by the University of Pennsylvania's Seth Rudman, a postdoctoral researcher.
New study looks at costs and benefits of paying for ecosystem services
People who live within a particular ecosystem can have great influence on its ecology, particularly if they are motivated by economic forces.
Loss of intertidal ecosystem exposes coastal communities
Artificial intelligence and extensive satellite imagery have allowed researchers to map the world's intertidal zones for the first time, revealing a significant loss of the crucial ecosystem.
New study explores ecosystem stability
A new study explores ecosystem stability. Its findings raise questions about the stability of our modern global system.
Connectivity explains ecosystem responses to rainfall, drought
In a new study published in the Proceedings of the National Academy of Sciences, researchers reveal techniques -- inspired by the study of information theory -- to track how changes in precipitation alter interactions between the atmosphere, vegetation and soil at two National Science Foundation Critical Zone Observatory sites in the western United States.
Fueling a deep-sea ecosystem
Miles beneath the ocean's surface in the dark abyss, vast communities of subseafloor microbes at deep-sea hot springs are converting chemicals into energy that allows deep-sea life to survive -- and even thrive -- in a world without sunlight.
More Ecosystem News and Ecosystem Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at