Necklace Shells on Tybee
Tybee Island has a large variety of species and colors of shells that wash up on its beach. Because of its position on the east coast, Tybee has northern and southern marine plants and animals, both along the shore and offshore, that produce a large diversity or variety of what we are likely to find (see “Tybee Diversity:” www.ceasurf.com). Along with the diversity of shell species, we also see a wide variety of shell colors that are often due to the past environment where a particular shell has been buried or spent time. For example, our most common bivalve (2-shelled) shells, the Ark shells, are often found in colors ranging from dark red, to orange, to gold, to white. During my Tybee Beach Ecology Trips, people often remark about how they are surprised to see Tybee’s vast array of colors and types of shells.
You don’t have to pick up many of our bivalve shells to find one with a perfectly round, small hole in it – just right for making a necklace. You will see these holes in our Arks, Surf Clams, Cross-hatched Lucines and others. It might surprise you to find out, though, that the animal that lived inside and made its shell did not make that hole.
To find out where that hole came from, we need to look at another mollusk, a gastropod or snail, that we also often find at the beach.
If you know where and how to look, it’s not too difficult to find Moon Snails on the beach at Tybee. Their round, light-brown shells often wash up along the high tide line; but you can sometimes find a live one burying through the sand in the mid and low tide, wet sandy parts of the beach.
If you find a live one, it will probably quickly withdraw back into its shell. But if you lay it back onto the wet sand or put it into some seawater, and be patient, it might re-emerge and start gliding across the surface. You will be amazed at how large its body is, outside of its shell, and wonder how-in-the-world it can pack all that body back into that small shell!
These Moon Snails are predators, and they like to eat many of those bivalves such as the Arks and Surf Clams that live buried down in the sand. To accomplish this, the Moon Snail glides through the sand, by producing and using lots of slime to help it move through the sand, until it encounters one of its clam-like prey, which quickly closes up for protection inside its two shells. The Moon Snail is not able to pry the two shells apart, but it wants to eat the soft-bodied animal that is inside. Inside the snail’s mouth is a tongue-like structure called a radula. The radula is like a small file or rasp that is hard and covered with tiny sharp teeth-like structures. A Moon Snail can extend this radula out of its mouth and drill a perfectly round, small hole through the bivalve’s shell. The hole is too small for the large snail to crawl through, but it can extend its radula down through the hole to the inside of the bivalve, where its soft body is. The snail will then slash its radula around in there, shredding and chopping the bivalve’s body into “soup.” The snail can then just suck the contents out, and it leaves behind a couple of empty shells – one of which has the hole in it! So the hole wasn’t originally a part of the bivalve’s shell; but instead that hole was pretty much the last thing that happened to that animal.
So while you’re beachcombing at Tybee, and you find that perfect size, shape and color shell with a hole in it for making your necklace; you can thank the bivalve animal that made the shell. But you need to also thank some predatory snail, like our Moon Snails, for drilling the hole!
Dr. Joe Richardson (Ph.D. Marine Sciences) conducts Tybee Beach Ecology Trips (www.ceasurf.com) for families and groups year-round at Tybee Island. Dr. Joe is a retired marine science professor who continues to conduct research throughout coastal Georgia through his consulting business Coastal Environmental Analysis. He can be reached at [email protected]