Known for mesmerizing onlookers with their graceful movements and transparent bodies, it's time to uncover the mystery of these curious creatures.
When we talk about jellyfish, we're often referring to the medusa stage in the life cycle of a variety of animals. True jellies, or scyphozoa, spend most of their life in the medusa stage and are probably what you picture when you think of jellyfish: a jelly-filled bell with lots of long tentacles hanging down. Animals like true jellies, box jellies, and hydroza's all belong to the same family, the cnidaria phylum, which also includes anemones and coral. Athough coral and jellies may seem like very diffrent animals, what brings them together is their venomous stinging cells!
We can think about the medusa stage as being the adult portion of a jelly’s life cycle. Medusa reproduce by spawning, creating a larva called planula. These little planula drift through the ocean until reaching the ocean floor. Then, the planula will attach to the ocean floor and develop into a polyp.
Polyps look similar to jellies, but tiny and upside down. Their mouths and tentacles are on the top, so they can eat any food that drifts down or floats by. These polyps can grow a small bud, genetically identical to itself, like clones! Buds eventually separate to form an entirely separate organism. Some species can reproduce like this until there is a whole new colony of polyps.
Eventually, when conditions are right, it’s time to move on. The polyp starts to grow taller and thinner and begins to divide into sections. These sections separate from the main body to become tiny jellies, or ephyra! These ephyra will leave the ocean floor behind and eventually grow into medusa starting the whole cycle over again.
Some species of moon jelly polyps have been observed skipping over steps of the life cycle, and growing from tissue fragments from healthy adult medusa. Even more famously there is "the immortal jellyfish." When times are tight, medusas of this species have been observed reverting into polyps, moving ‘backward’ through their lifecycle!
Jellies are found in oceans all over the world, at the surface, deep beneath the sea, in warm water, cold water, and even freshwater! They cannot fight a current and are considered drifters. The ocean keeps them in constant flow.
Despite their go-with-the-flow life, most jellies are carnivorous hunters. They mostly eat other plankton (including other jellies!), but sometimes even fish and crustaceans. Here at Ripley’s, we feed them fish eggs and frozen krill, usually blended into a smoothie, along with brine shrimp larvae that we grow on-site.
To catch their prey, jellies use their stinging cells called nematocysts. Jellies have thousands of nematocysts along their tentacles and some, like the true jellies, have more within their bell to help them keep larger prey. When something touches the tentacles, the jellyfish stings. The nematocysts shoot barbs that release venom, which stuns or kills the prey. Once the prey is incapacitated, the jelly will pull the prey up into their bell to be digested.
Jellyfish are hunted by certain species of fish, crustaceans, and sea turtles. Unfortunately for those animals, a floating plastic bag looks a lot like a floating jellyfish—drifting and transparent. Research has shown that more than half of all sea turtles have eaten plastic. One of the five giant garbage patches in our oceans, the Great Pacific Garbage Patch, is estimated to contain more than 80,000 tons of plastic. All of that plastic in the ocean means that animals are getting more and more likely to have accidentally eaten plastic in their lifetimes.
You can aim to reduce the amount of waste you produce and make sure that the things you throw away end up in the right place like compost and recycling bins. You can also organize with your community to clean up your local shoreline or waterway. Many hands make light work, and a group of people working together to safely pick up litter can have a big impact!
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