Shell growth in estuaries

Ok kiddo, have you ever seen a seashell before? They come in all different shapes and sizes, right? Well, those shells actually come from living creatures called mollusks that live in the ocean.

Now, there are some mollusks that live in a place where the ocean meets a river. This place is called an estuary. In the estuary, there is a lot of fresh water mixed with salt water from the ocean.

These special mollusks, called bivalves, have to adjust to living in this mixed water environment. They do this by growing their shells differently than their ocean-living mollusk cousins.

Instead of growing their shells in a circular shape, these bivalves grow their shells in a long, skinny shape with a hinge in the middle. This special shape allows them to live in the sandy, muddy bottom of the estuary without getting washed away by the moving water.

But the real trick to their shell growth is how they add on new material. You see, as they grow, these bivalves actually add material in layers to their shells. They start by adding a small layer and then they add more and more on top of it over time as they grow.

The cool thing is that each layer looks different depending on the season and the amount of freshwater and saltwater in the estuary. By looking at these layers, scientists can learn a lot about the environment during the time the bivalves were growing.

So there you have it, kiddo. Bivalves in estuaries grow special shells to help them live in a mixed water environment, and they add on new material in layers that scientists can study to learn about the environment.