Sunday, January 20, 2008

It's the calcium, stupid!

I've been doing a little thinking about calcium. Snail's have one absolute requirement that has a rather striking impact on their distribution and diversity. Calcium-rich environments have enough free building material for snails to manufacture and maintain an external shell. It should come as no surprise that the dolomite (a type of calcium-magnesium carbonate rock) outcrops in eastern Wisconsin have a rich snail fauna: dozens of species can share the same square meter space quite happily.

So what about areas that do not have calcium carbonate bedrock? For instance, here on the North Shore of Lake Superior, there aren't any carbonate outcrops. What do snails do to get their calcium? Well, plants contain calcium. But there are also igneous rocks that have calcium as a major constituent. Magnesium, and calcium are important cations in mafic igneous rocks, and many of the outcrops up here are these types of rocks. Along rock ledges near streams, there is a pretty impressive snail fauna crawling around, relatively unnoticed.

More about snails in northeast Minnesota will come in the following months...


  1. They also eat each other's shells & the same calcium carbonate gets recycled. In forests where the soil & the rocks are not high in calcium, shells are probably the major supply of calcium for snails & other animals.

  2. I have several Apple Snails Pomessii Bridegi (spelling?) and some of them have tiny holes in their shells. I am positive that it is due to my normal ph level of almost 7 (which is considered slightly low for snails). What can I add to freshwater aquariums - besides egg shells - as a suplement. The bottles of calcium in the pet store are for marine aquariums only. Egg shells don't seem to do the trick.