One of the oldest groups of animals alive today, jellies often appear elegantly simple to the casual observer. But spend a little time with one of our jelly lab aquarists and you get the impression that, when it comes to jellies, there is a lot more to them than many people suspect.
Here at the New England Aquarium, we frequently have a dozen or more species of jellies (like the moon jelly). Some are on exhibit for visitors to see while others are raised behind the scenes to be sent to other aquariums all over the world.
Younger lagoon jellies (Mastigias papua) contain photosynthetic algae. As they mature, they need less light and loose their bluish color.
In order to successfully raise jellies, our aquarists must be familiar with their unusual reproduction strategy. Like something out of a science-fiction film, jellies go through several life stages that are drastically different from one another. Adult jellies, called medusa, can reproduce sexually by releasing eggs and sperm. Fertilized eggs become free-swimming planula larvae.
The lifecycle of a local species, the moon jelly, is so complicated that it helps to have an illustration courtesy of Senior Aquarium Educator Lisbeth Bornhofft.
Jellies can also reproduce asexually by forming anemone-like polyps (jellies and sea anemones, along with corals, are related to each other) that strobilate, or bud off, identical copies of themselves. These free-swimming “buds” are called ephyra. In some species, several ephyra can bud off of one single polyp.Since the jelly lifecycle in the wild is seasonal, our aquarists recreate a temperature shift from winter to spring, or spring to summer, to cause the polyps to strobilate.
Thumbnail-sized ephyra of purple-striped jellies (Chrysaora colorata)
Some ephyra are photosynthetic; they have symbiotic algae called zooxanthaellae that converts sunlight into food. Other ephyra are quite content to munch on tiny brine shrimp. Feeding and growing, they will eventually “bell over” into an adult medusa. This is when the shape of the jelly changes from a pointy star to more of a solid dome.
Despite their small size, these ephyra are already predators. If you look closely, you can see the brine shrimp we raise and feed to our jellies.
Here at the Aquarium, we have jellies on exhibit in both the Thinking Gallery and in the West Wing. While most of the jelly raising happens behind the scenes, we currently have Cassiopia jellies reproducing in the live mangrove exhibit. These jellies are often referred to as “upside-down” jellies since as adults they settle to the bottom of shallow, sunny tropical waters and use their bell like a suction cup. Being upside-down allows the photosynthetic algae to get plenty of sun!
Below is a video of both adult and ephyra stages of Cassiopia on exhibit. Or better yet, come to the New England Aquarium and see them for yourself!