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Marsh Periwinkle (Littoraria irrorata): The Fungi-Farming Sea Snail

April 18, 2012  •  Leave a Comment

Periwinkles. When you see or hear that word, you either think of a type of a beautiful, flowering planet or a small, slimy snail. In typical EpochCatcher nature, I am discussing the latter. Periwinkles are fascinating creatures, although--under normal circumstances--you probably wouldn't pay them any mind.  In their typical habitat, Atlantic and Gulf Coast salt marshes (who knew?), marsh periwinkles graze on cordgrass, algae, and leaf fungi, and you hardly see any of their soft bodies.  If you even notice them, you'll only see a series of conical shells clinging to cordgrass, sand, mud, and rocks.
However, these simple, small gastropods are more intricate than they seem: they are the only known mollusks to practice fungiculture. What's fungiculture? Fungiculture is, as the name suggests, the act of growing and harvesting fungi. So how do these armless, legless creature manage this feat?

Marsh periwinkles use their radulae--a toothy, tongue-like organ--to create gashes in live cordgrass, usually cutting entirely through the leaf, so they can feed on the juices inside. During this process, the snails defecate (see: poop) on the grass, spreading their nutrient-rich feces (nutrients provided by the juices from inside the leaves) on the gashes in the cordgrass. Charming, I know. But the snail poop acts as a natural fertilizer for fungus.

You see, the gashes in the cordgrass make the leaves vulnerable to fungal infection, and the snail poop increases the infection, but this is exactly what the periwinkle (and the fungi) wants. The fungus is the periwinkle's favorite food, and it relishes this delicious treat like candy. However, unlike candy, the fungi is very healthy for periwinkles and makes them grow big and strong.  

But this peaceful relationship between snail and fungi is not without disruption. Predators, like the boat-tailed grackle, eat periwinkles. Yet, as sad as this may seem, this is a part of the natural order.  The periwinkle's fungiculture reduces cordgrass growth, keeping cordgrass growth in check. Likewise, the periwinkles' predators keep the periwinkles' populations in check, preventing the periwinkles and fungi from completely decimating the cordgrass.  So, in the end, everyone keeps everyone else from taking over. It's a natural system of checks-and-balances.


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