Jellyfish 101

What is a jellyfish, and how do you take care of them?! A question on every visitor’s mind.

Being neither fish nor delicious fruit preserve, the name “jellyfish” is a bit of a misnomer.  Typically referred to as sea jellies, or just “jellies”, these animals belong to a larger collection of animals referred to as Cnidaria, and are more closely related to sea anemones and corals than they are to actual fish. They evolved over 580 million years ago when their ancestors laid claim to the planktonic, venomous marine predator niche of the food chain. And they’ve held onto it firmly ever since.

That being said, jellies are little more than a set of floating stomachs with stinging arms, a simple network of nerves and a reproductive system – so how much work can really go into their care? Let’s find out!

First, you just need to simulate the vast and fathomless open ocean in a relatively small space. How hard could it be?!

In order to recreate a jelly’s natural environment, we have to build a tank that ensures they aren’t exposed to powerful currents, walls, corners, edges, holes, any solid objects whatsoever, excreted waste, old food, microscopic organisms, other jellies – you get the idea. Sea jellies’ health will rapidly deteriorate if they have prolonged contact with anything solid. So, in terms of build, most jellyfish tanks are rounded and have painstakingly balanced water flow to keep jellies suspended off of the walls and floor. Similar to the ceiling moon jelly tank (pictured below) in our Planet Jellies gallery.

Second, you need to provide a constant, even supply of a variety of foods all day, every day.

Jellies are opportunistic carnivores. In the wild, this means they are continually pulling food out of the water. At the Aquarium, this means that we have to provide a near-constant supply of things for them to catch, a feat managed by our behind-the-scenes “live food” cultures and specially blended “shakes” made up of frozen krill, fish eggs, and other goodies. Delicious!

Each day, one aquarist is responsible for preparing the population of freshly hatched brine shrimp that will be fed out, via a low drip, to all of our tanks. Just as much work goes into keeping up our live foods as it does to care for any of our exhibit tanks; they have to be fed, their tanks have to be cleaned, and their health needs to be closely monitored to ensure our animals are getting the highest quality food possible.

Third, you need… well, jellyfish.

Jellies reproduce by broadcast spawning, which means the males and females release sperm and eggs into the water. These gametes meet up and create a small grain-like “planula” that will find a nice place to settle down into a polyp, which resembles a small sea anemone. These polyps will break off into several flower-like ephyrae, which eventually transform into medusae – the final life stage that most people recognize as “jellyfish”.

Perforated plates or mesh left in tanks containing adult jellies are ideal settling grounds for polyps, so our cultures behind the scenes and on-exhibit are always growing and changing! (When touring the Aquarium, be sure to check out the life cycle display in Planet Jellies.)

Finally, all that’s left is keeping up with the cnidarians.

Day to day maintenance of our jelly tanks is an involved and convoluted dance, since any interaction between cleaning equipment and jelly could result in injury. At the same time, our jellies also need their tanks to be kept clear of algae and other microscopic organisms that could damage them. To help combat this, once every few months each exhibit will have its inhabitants moved out to a holding tank overnight, and a diver will either enter the tank to scrub down all the surfaces, or the tank will be bleached, emptied, and refilled with fresh salt water.

Though it can be a bit disorienting with the ever-changing lights on our jellyfish exhibits, pay attention the next time you swim by and you might be able to see how the water flows around our tanks, spot some speck-sized brine shrimp zooming around, or even see some brand new baby ephyrae!

Have a question about the Aquarium, or something you would like to see on Deep Sea Diary? Drop us a line in the comments below for the chance to be featured in our monthly Q&A post!