Shell Game

Half a million people live in Poznan, Poland, and yet it takes but eight mollusks to make sure their water is pure.

Huh? What say, Mark? Mussels are checking the water purity of a large city? Next thing, you'll tell me that computers are running the elevators and the traffic lights.

Fun fact: They do, and they do.

The Warta River supplies the water for the Poznanians. 

What you see in the picture is a zebra mussel. It turns out that they are very sensitive to pollution. Instead of going out to eat, or cooking for themselves, they feed by filtering water in the river they live in, trapping microscopic plankton.

And you know, there's nothing better than seafood! The Plankton Platter also comes with fries and slaw!

All right. As the mollusk filters the water, if there is something funky afloat, it closes the valves of its shell. The eight mollusks who work for the city in Water Purity each have a magnet attached to their shell. There is a water-sealed relay in the mussel that sends a signal to a computer to say "I just clammed up."

If more than 3 of the 8 shells close up, that's a signal to the Water Dept. that the river water is bad, and it's time to switch over to the tanks of clean water set aside for just such eventualities.

And get this! These mollusks live for between 4 and 8 years, depending on whether they smoke. BUT the retirement plan! They get pensioned off after just three months of work, and are sent to a nice clean retirement tank.

And this is kind to the animal, sure, but also, after a short period of time, these guys get used to foul water and stop noticing the low quality. 

They are replaced with younger, sharper mussels, and life goes on.

It's a lot like humans, without the nice retirement party.