Pete McIntyre snail collecting as local people watch. Photo © Ellen Hamann

What Can Snails Tell Us About Water Quality?

August/September 2016

For the past 20 years, biologist Pete McIntyre has traveled to Africa’s Lake Tanganyika, Earth’s second-largest freshwater lake by volume, to study freshwater snails found nowhere else in the world. McIntyre, a professor with the University of Wisconsin-Madison, explains why these snails are important and what they tell us about pollution in the lake.

A version of this article originally appeared in the August/September 2016 issue of Nature Conservancy magazine. Read more at — NCM

Q: First off, why study snails?


The snails of Lake Tanganyika are very diverse by freshwater snail standards. They’re interesting biologically, but we can also use them as sentinels for change in the environment. Unlike fish, they’re stuck at the bottom of the lake. So if some aspect of the environment changes, they’re also stuck with whatever bad things happen to the system.

Q: What sorts of things have they shown you?


We demonstrated that you get a dwarfism phenomenon due to siltation near villages. Outside Mahale Mountain National Park [on the eastern shore of the lake], you’ve got thin trees or no trees, and inside the park you’ve got pretty spectacular forests. That [differentiation] basically extends out into the water, and we see what we now understand as a predicable shift: the snails get smaller.

We also collected snails around villages where people are washing their clothes or cleaning their fish. What we tried to do there is use the snail tissue as a sentinel for nutrient pollution.

Q: How does that work?


Nutrients coming into the water get taken up by the algae, the snails eat the algae, and we analyze the snail tissue. Lo and behold, we got a beautiful relationship between the size of the village and the amount of human-derived nitrogen stored in snail tissues.

Snails of the Lavigeria species. The two snails are the same species, but the one on the right has a crab scar (it must have survived a pretty big attack!). Photo © Ellen Hamann
Snails of the Lavigeria species. The two snails are the same species, but the one on the right has a crab scar (it must have survived a pretty big attack!). Photo © Ellen Hamann

Q: And that pollution can be harmful to more than just snails, right?


Right, but in fact the silt eroding from the denuded land is probably worse for the snails. The combination of silt and pollution also hits the fish community hard. And remember that this is the same place where people draw their water. All kinds of bad things can happen in that situation, such as diarrheal diseases or liver flukes.

Q: Your team has helped nonprofits in the area, including The Nature Conservancy, the Jane Goodall Institute and Pathfinder International. How do you work with these groups?


We’re providing a bio-indicator tool that can help measure the efficacy of their efforts to reduce pollution — how is this changing the degradation of this amazing freshwater ecosystem? Both as a biologist and as a human being, I’ve got compelling reasons to want the condition of Tanganyika to improve. Our partners are doing the hard work of on-the-ground interventions, and the snails can help us understand what actually works.

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  1. Benthic macroinvertebrates including snails are good bio-indicator of water quality especially those of organic pollution load in the water. These organisms have been used as a tool for biomonitoring since long as they have very limited power of locomotion and can survive for relatively longer period. Shannon Species Diversity Index help in quantifying the water quality. Many species among the benthic macroinvertebrates help in reducing the organic load by consuming it.

  2. Very informative. I’m a feisty Mom Nature advocate and know that all Her childr’n gotta place in the choir. ButI sometimes don’t get a good read regarding Her smaller ones. So thank you! ?✌