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Jellyfish in Maryland's Waters - July 16, 2017

                Carried by currents throughout the world’s oceans, bays, and rivers, jellyfish are some of the most interesting, yet sometimes painful, animals found in the aquatic ecosystem. These gelatinous, brainless, and potentially dangerous creatures are found worldwide and are well adapted to their aquatic homes.

                Jellyfish belong to the cnidarian family; a group of animals, including corals, that all have nematocyst cells that they use to help capture prey. Nematocysts are like tiny harpoons that are attached to a trigger. When touched, the trigger activates, resulting in the barb firing off and injecting the prey with the imbedded poison. The specific type of poison that is injected into the prey is dependent on the jellyfish species, and can range from a mild irritant to a potent neurotoxin.

                Jellyfish are technically planktonic, which means they are free floating and move mostly by currents and wind movement; however, they are much larger than most other planktonic species, classifying them as macro-zooplankton. While jellyfish are planktonic, they can move by pulsating their bell or by using rows of cilia. Although they can have a set direction, they are weak swimmers and will not fight against the current.

                Several distinct species of jellyfish can be found here in the Chesapeake and Coastal Bays. One of the most common species is the sea nettle. This jellyfish has a milky white bell, several oral arms to move and digest prey, and anywhere between 8 to 24 tentacles, which can be anywhere between 4 to 5 feet long and armed with stinging nematocysts.

                Sea nettles are extremely effective predators and can consume small fish, shellfish larvae, worms, zooplankton, and even other types of jellyfish. While they do not actively hunt, the sea nettles will drift along the top of the water column and entangle prey in their tentacles. The prey will be injected with poison from the nematocysts and eventually die, at which point the jellyfish can begin digesting it. Sometimes prey will struggle so much that they rip off tentacles, however many species of jellyfish have the ability to regrow them.

                Moon jellies are another common jellyfish species found in our bays and waterways. The moon jelly looks like a clear, flattened disk shape with a pink, four-leaf clover design in the middle, which is made up of four horseshoe shaped gonads.  Most moon jellies have a four-leaf clover, but three and up to seven-leaf clovers have been seen.  Moon jelly tentacles are much shorter than the sea nettle tentacles, but unlike sea nettles, moon jelly stings are much more mild and do not pose much of a threat to humans.

                Moon jellies can eat anything from plankton, to mollusks, copepods and even crustaceans. Moon jellies will actually change color depending on their diet. If the jelly feeds extensively on crustaceans it turns a pink or lavender color while if it feeds mostly on brine shrimp, it will turn an orange hue.

                One jellyfish species that can be found in our bays during the winter months is the lion’s mane jellyfish. This species is the largest known jellyfish species in the world with bells as large as 6 to 7 feet across. However, we tend to find smaller versions here in Maryland. This jellyfish is brownish-red in color and has long tentacles hanging from the edge and middle of the bell. Like sea nettles, the lion’s mane preys upon fish, shrimp, comb jellies, and other small creatures and their sting is painful to humans.

                In recent years, a few Portuguese man o’ war have washed ashore in Ocean City. While this creature is often lumped together with jellyfish, it is not a true jellyfish at all. The Portuguese man o’ war is actually a siphonophore, or a colony of organisms working together. The main sail, the part sticking up out of the water, is actually one organism, while the tentacles, digestive and reproductive areas are all distinct organisms as well. The tentacles for the Portuguese man o’ war can reach lengths of over 150 feet; however, the average is more towards 30 feet. The tentacles are covered in nematocysts and the sting of a Portuguese man of war is very painful for humans, and potentially deadly.

                Unfortunately we might be seeing more of these gelatinous creatures in coming years. A recent study found that jellyfish fish blooms are increasing in frequency in 62% of major marine ecosystems. Overfishing has resulted in a decline in the primary predators of jellyfish, such as sea turtles and tuna, and a decline in their competitors, such as sardines and herring. All these factors allow for the increase in jellyfish populations. And that increase is having an impact on those ecosystems.  Since jellyfish eat the eggs and larvae of fish, recruitment of commercial fish lessens considerably, causing further fish population declines. One example of this was when the comb jelly, a cousin to jellyfish, was introduced into the Black and Caspian Seas. The comb jellies outcompeted the commercial fish for food, while also feeding on their eggs and larvae. The resulting fish population crash wiped out a $350 million dollar fishing industry.

                A number of remedies have been identified to counteract the pain from jellyfish stings.  Quickly flushing with freshwater, then applying meat tenderizer often tends to be a good anecdote.  Although it merely assuages the pain and does not eliminate it.  Time works best for most, but for severe exposure it is best to see a physician.

Jackson is the former Education Coordinator for Maryland Coastal Bays Program and current graduate student at Clemson University. 



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