Tennessee Aquarium senior aquarist Sharyl Crossley works with a lot of oddballs. That's because her primary duties include caring for creatures that have no eyes, feel like wet Jell-O and can sting you in a micro-second. "I like jellyfish because they are so weird, " Crossley says with a smile. "They're very alien and I think that intrigues most people. So, I get a lot of really good questions about jellyfish."
Want to know more about these free-flowing life forms from the deep? Read on to get Crossley's jammin' good answers to frequently asked questions about jellies.
What are Jellyfish?
Jellyfish are animals. Chemically, jellies are composed of at least 95 percent water with some proteins and salts making up the other 5 percent of their bodies. True jellyfish belong to the Phylum Cnidaria along with corals and sea anemones. Comb jellies (Phylum Ctenophora
) are not "true" jellyfish because they lack those really important stinging cells. Other jelly-like critters include a variety of swimming mollusks (sea butterflies and sea elephants) and pelagic tunicates (salps, doliolids, and pyrosomes). The characteristic that unites all these unrelated animals is their delicate gelatinous tissue.
Are there jellies in Tennessee?
Yes, there are jellyfish in Tennessee. The freshwater or peach blossom jellyfish, Craspedacusta sowerbii, is unlike other jellies because this is the only species that can be found in freshwater rivers, lakes and ponds. Peach blossom jellyfish are not native to the Tennessee River, but have been spotted in the state's waterways on many occasions. It has also been found in Canada, throughout Europe, Asia, Australia, Malaysia, Central America, and even Iraq! If you are lucky enough to encounter this species of jellyfish, don't worry too much. This jellyfish species is quite small and has no noticeable sting.
What do jellies feel like?
This may sound a little obvious, but they feel like wet jello. Some feel thicker or tougher than others, but all feel quite slimy.
Are any of the jellies at the Tennessee Aquarium deadly?
None of the jellies at the Tennessee Aquarium are considered deadly. Although many species of jellyfish can have irritating mild to moderately painful stings, very few are actually considered deadly.
Where do jellies come from?
Jellies can be found in just about every marine habitat and every ocean. Jellies live in estuaries, bays, harbors, and the open ocean. Some are even in the deepest ocean basins. They're found from the warm waters near the Equator to the frigid waters of the arctic and antarctic. Some single species of jellies, like the moon jellyfish, can be found all over the world.
How do jellies swim?
Jellyfish mostly drift with the currents, but they can swim to move short distances or redirect themselves. By contracting muscles in their bell, water is forced out and the jelly is propelled in the opposite direction. The muscles then relax and the bell gently springs back into its "open" position. This pulsing motion closely resembles an umbrella being closed and opened. At the cellular level, jellyfish muscles look almost identical to human muscles, but their "muscles" are only one-cell thick!
What's the largest jellyfish?
The lion's mane jellyfish (Cyanea capilata
) is the largest jellyfish species. The largest specimens of this giant can attain a bell diameter of 8 ft, a weight of 330 lb and can possess tentacles as long as 120 ft or more.
What's the smallest jellyfish?
The smallest jellyfish species is thought to be the Irukandji jellyfish (Carukia barnesi
). Its bell rarely exceeds 2mm when fully grown and it is considered to be one of the deadliest jellies in the world.
How long do jellies live?
In the wild, jellyfish medusas typically live only for about one season, around 5-8 months. That's just long enough to eat a lot, grow big and reproduce. New medusas typically appear the next year to start the cycle all over again. At the Tennessee Aquarium, some of the large jellies like the moon jellyfish and the sea nettles can live up to 2 years. Some of the smaller species, like umbrella jellyfish and blubber jellyfish, have a shorter life expectancy of only 6-8 months
Where are their eyes, mouth, and stomach?
Most jellyfish don't have eyes. They rely on a very basic nervous system and small sensory structures called rhopalia, located around the edge of the bell. Within the rhopalia may be special structures to sense light (ocelli) or gravity (statoliths). When it comes to jelly vision, box jellies have the best sensory cells. They have complex ocelli that closely resemble the image-forming eye of squid and vertebrates. These jellies have good enough "eye-sight" to avoid large objects and distinguish between potential prey and non-prey.
What do jellies eat?
Most jellies feed on some type of zooplankton, small animals that drift with ocean currents. Some even eat other jellies. The jellies with the most potent stings usually dine on bigger food like whole fish or prawn. At the Tennessee Aquarium, the jellies' diets are a little bit different. Live natural plankton is not available to us because we are not located near an ocean. Every morning newly hatched brine shrimp (Artemia) are harvested to be fed to the jellies. These small crustaceans, popularly known as sea monkeys, make up the basis of our jelly diets. Once hatched, the brine shrimp are fed vitamin-rich supplements to make them more nutritious for the jellies. Other foods, including - but not limited to - frozen blood worms or mysis shrimp, chopped moon jellyfish, fish eggs and rotifers are added to the diets of different jellyfish in order to maximize the nutritional variety offered.
How do jellies eat?
Typical jellyfish have stinging tentacles that trail from the edge of their bell. As jellies float through the ocean they use these tentacles to snag their prey. After the food is caught and immobilized by the stinging cells, it can be passed to the mouth of the jellyfish. The mouth is located in the very center of the underside of the bell. Once in the mouth, the food is digested in the stomach (or stomachs) of the jellyfish. Because of their mostly transparent bodies it's easy to see what a jellyfish has recently eaten.
Where is the part that stings you?
The same tentacles that jellies use to catch food are the parts that can sting you. These tentacles carry the highest concentration of stinging cells in the jellyfish body. On west coast sea nettles, these tentacles are long and brown in color, but on moon jellyfish they are wispy, white, and hair-like. The oral arms, the thicker frilly appendages under the bell, are also armed with venomous stinging cells. These stinging cells aren't there just to terrorize beachgoers, they are essential to the jellyfish's survival and its ability to capture food. The microscopic stinging cells, or nematocysts, look like tiny harpoons coiled up within a capsule. When the jellyfish brushes against something like plankton or a swimmer's leg, the nematocyst capsule pops open and the tiny venom-laden harpoon is propelled into its target.<< WATCH VIDEO
. The nematocysts are typically organized in batteries causing hundreds or thousands to be discharged simultaneously. This harpoon discharge is one of the fastest biological processes and takes only a few microseconds (1 sec = 1,000,000 microseconds) from start to finish.
Have you ever been stung?
I have been stung before while working with jellies. I do what I can to avoid it, but I spend almost eight hours everyday working with different species of jellyfish, so a sting once in a while is inevitable. Fortunately, the jellies at the Tennessee Aquarium do not have very painful stings. I normally get itchy bumps, similar to mosquito bites, on the sensitive skin between my fingers or on my inner forearm. Calloused skin, like that on the palm of the hand, is too thick for most stinging cells to penetrate - so I never get stings on the palms of my hands. It's also important to remember that jellies have very little control over what or who they sting. The trigger for their nematocyst is involuntary, and relies strictly on specific chemical and mechanical cues to fire.
Are there any jellyfish that don't sting?
All true jellyfish have stinging cells and therefore "sting." However, not all true jellyfish have stinging cells and venom that are strong enough to affect humans. Our skin is our first defense against jellyfish stings. If the stinging cells, nematocysts, are not large enough to penetrate this barrier, then nothing happens and we don't feel like we have been stung.
There are lots of gelatinous creatures in the ocean and many of them are sometime referred to as 'jellies', even though they are not true jellyfish. Good examples of these are the comb jellies, such as the sea walnut, Mnemiopsis leidyi. Comb jellies look like a jellyfish, move and act just like a jellyfish, but are actually Ctenophores. Ctenophores use sticky mucous, not stinging cells, to catch their prey. If you get stung by a jellyfish at the beach - what should you do?
Before you head into the ocean, learn about what species you might encounter at the particular beach you are visiting and check the surf reports for jellyfish warnings. This will help you make an informed decision about getting in the water. Most jelly stings are minor. But if you feel pain after a close encounter with a jelly, then you've been injected with venom from thousands of tiny nematocysts. Because they can still function even when detached, it's important to remove any tentacle pieces that may be stuck to the skin as soon as possible. It is best to pluck them off or rinse them away with seawater. Rubbing or rinsing with freshwater will cause more stinging cells to fire and increase your pain. Mild to moderate stings may cause a burn-like, red rash with pain, itching and raised bumps on the skin. Symptoms will usually disappear within about a day without any treatment. Ice packs may help reduce pain if applied for a few minutes to the sting site. Stronger stinging jellyfish, such as from the Portuguese man-of-war, will pack a bigger punch. Pain can be severe and last for several hours accompanied by welts and lesions lasting several days. After such an unpleasant encounter, rinse with seawater, apply vinegar, meat tenderizer, or sodium bicarbonate to help disable any remaining nematocysts. Ice packs and application of topical analgesic creams can also help soothe a sting. Immediate medical attention is required in cases of severe reactions. A severe reaction to the toxins may include anaphylactic shock, extreme pain, respiratory and cardiac distress. Fortunately, this level of sting is rare in the waters that surround the United States.
How do jellies reproduce?
Jellies have a very complex life cycle which includes four phases. First, is the medusa phase. When most people think of 'jellies', they picture the medusa phase. This is a free swimming phase that is responsible for the sexual reproduction of the species. Each individual medusa is male or female, and during spawning will release gametes, sperm and eggs, into the water. When a jellyfish egg is fertilized, it will develop into the second phase, known as a planula (plan-you-lah). The microscopic planula will swim for about 48 hours, settle onto a hard surface, and develop into a polyp. Polyps are the asexual phase of the life cycle and closely resemble a tiny anemone. They can reproduce in two distinct ways, through budding and through strobilation. During budding, an offspring grows from a body part of a parent polyp. A single polyp can give rise to an entire colony of polyps by budding. During strobilation, the top portion of the polyp divides into segments. Each segment will eventually break away from the polyp and become free swimming. This phase, known as ephyra, will eat and grow and eventually undergo a metamorphosis into a medusa. Not all jellies stick closely to this plan though. For example, small hydromedusas, like the umbrella jelly, skip the ephyra phase all together.
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