Life for a jelly in an aquarium is almost like living on an amusement park ride. After all, they live in displays called kreisels, which is the German word for “carousel.” All day, every day, they ride a circular current that keeps them in motion.
Jellies may seem low-maintenance, what with them having no brain thanks to a simple central nervous system, but keeping and caring for them is tricky business. Did you ever wonder why their tanks are typically round? Because they are so delicate, if they were to wind up in a corner of a tank, they could get stuck, or worse, die. They are planktonic, and as such, cannot swim against strong currents.
To exhibit jellies, they need to be housed in specialized tanks. As you make your way through The Maritime Aquarium, you’ll find that our jellies call three different types of tanks home: the kreisel, split kreisel and cylinder tanks.
Whatever their design, all tanks must take into account the fact that, despite being creatures of the sea, jellies are not exactly the best swimmers. A gentle circulation of water is used, rather than typical aquarium filtration systems that would suck the jellies right in. The circular flow serves a two-fold purpose: it gives the jellies the ability move around the tank and allows food to get to them.
A kriesel tank has a flattened cylindrical or stretched-out design that allows water to flow in one circular pattern. Jellies do just fine in the ocean, but in a tank, the circulation helps them from getting stuck on the bottom. These tanks have laminar flow plates that look like a bunch of straws glued together. The plates gently blow the jellies away from the outflow screens, so they don’t get stuck, while also keeping them suspended in the water.
(From left to right: 1. Visitor view of a kreisel exhibit at the Maritime Aquarium. 2. View of a kreisel tank from the back. Jellies float in an out of view as they move with the circular flow. 3. Water is filtered in through pipes at the top and bottom of the tank. Also seen here are the straw-like flow plates.)
A pseudo kreisel, or split kreisel, operates in the same way as a true kreisel tank, but often uses a spray bar instead of a laminar flow plate. A spray bar is a tube with holes drilled down one side, like a lawn sprinkler. These tanks can be incredibly versatile. Our split kreisel tank uses a spray bar that blows water in either direction. As you can see in the photo from our Marine Care & Culture Lab, the rectangular tank has been modified with added curves on the sides and in the middle to guide the circulation streams to keep the jellies on track.
The cylinder tank is arguably the most dramatic of the jelly exhibits. Water enters the tank from an inflow pipe at the top. The bottom corners of the tank are rounded off, allowing the jellies to flow down the center of the tank, and up along the sides. A smaller inflow pipe underneath the perforated plate on the bottom keeps the jellies from getting stuck.
Here’s a behind-the-scenes look at how the jellies move within the circular flow:
So the next time you’re at the aquarium and find yourself captivated by the hypnotic movements of the jellies, just remember: they’re a lot more complicated than they seem.