There are a lot of egg cases that wash up on our beach. Most of them are laid by mollusks, and anchored in the sand. If you stop by the nature center, you can see a lot of them– and most of the ones we see are from our most common whelk, the knobbed whelk. The knobbed and lightning whelk egg cases have a two-sided edge to the capsules. The channeled whelk has more of a hard, single chine, and the pear whelk is a little spiky.
The one we found most recently is from a channeled whelk: note the single, fluted edge. Whelks lay egg strings 2x per year (Sept-Oct. and April-May), although scientists aren’t sure whether each individual lays more than once a year. They may be triggered to lay eggs by water temperature– according to SCDNR, they are triggered to lay egg chambers when the water temperatures reach 68 degrees F.
The first few chambers are often empty, and used to anchor the string into the sand. Each capsule has about 35 eggs per chamber, and strings can be more than 150 capsules long. Most of the egg strings we find on the beach are empty; you can see the tiny hole where the tiny mollusks have eaten their way out. As they grow, they feed on each other in the capsules– you can find the shells of the weaker siblings in the stranded egg cases.
This case still has developing eggs within it– you can see the albumin in the chamber. We threw the case back in the water in the hopes that the babies would develop. They develop slowly– incubation time can range from 3-13 months.
In the nature center, you can see knobbed and lightning whelk egg cases, as well as the tiny shells left inside. These kids at camp are investigating one of these cases: