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Stinging Flotillas in Marylands Waters - July 5, 2015

    Carried by currents throughout the worlds 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 very well adapted to fit their aquatic homes.
 
    Jellyfish belong to the cnidarian family, a group of animals including corals that all have nematocyst cells which they use to help capture prey. Nematocysts are basically like tiny harpoons that are attached to a trigger. When touched, the trigger activates which results in the barb being fired 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 are moved mostly by currents and wind movement, however they are much bigger than most other planktonic species, which is why we classify jellyfish as macro-zooplankton. While jellyfish are planktonic, they can move somewhat by pulsating their bell or by using rows of cilia, however they are weak swimmers and will not fight against the current. 
 
    The lifecycle of a jellyfish is mostly divided into two different stages, the polyp and medusa stages. The polyp stage is the early lifecycle stage for jellyfish, and unlike the adult form, polyps cannot move at all. 
 
    Jellyfish larvae, known as planulae, will be released by the adult female jellyfish and are carried by currents until they eventually settle on the bottom. After they settle on the bottom, the larvae will attach themselves with a glue like substance and then will grow into their anemone-shaped polyp form. The polyps will feed and grow until it is time for them to reach their adult stage, at which point they will transform into a series of small stacked discs. Each disc then separates from the base of the polyp as miniature versions of the adult known as ephyra. The ephyra will continue to eat and grow until it finally starts to resemble the adult version. The adult and ephyra versions are what we call the medusa stage, and have the typical bell shape with dangling tentacles. 
 
    We have several distinct species of jellyfish here in the Chesapeake and Coastal bays. One of the most common species is the Sea Nettle. This jellyfish has the typical milky white bell, several oral arms to move and digest prey, and anywhere between 8-24 tentacles. These tentacles can be anywhere between 4-5 feet long and are 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 as prey creatures get tangled in their tentacles and injected with poison from the jellies nematocysts, the prey will eventually succumb and die at which point the jellyfish can move it towards their mouth and start digesting it. Sometimes prey will struggle so much that they will rip off tentacles, however many species of jellyfish have the ability to grow these back later. 
 
    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. Moon jelly tentacles are much shorter than the sea nettle tentacles, and are found around the edge of the bell of the moon jelly. Unlike sea nettles, moon jellies 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, then the jelly will turn a more orange hue. 
 
    Another typical jellyfish we find here is the Lions Mane jellyfish. While this jellyfish can have a bell as large as 6 feet across, we typically tend to find the smaller versions here in Maryland. This jellyfish is generally brownish-red in color and has long tentacles hanging from the edge and middle of the bell. Like sea nettles, the lions man jellyfish prey upon fish, shrimp, comb jellies and other small creatures and their sting is certainly painful for humans.  
 
    Unfortunately, this summer we have seen a few Portuguese man of war wash ashore here in Ocean city and even further North as well. While this creature is often lumped together with jellyfish, it is not a true jellyfish at all. The Portuguese man of 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 of 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 even potentially deadly. 
 
 
This is the Maryland Coastal Bays Program Column for the week of July 5th, 2015. 


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