Sea Nettles and Jellyfish



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Globular creatures appear each summer, driving everyone from the waters of the Chesapeake Bay. These pulsing gelatinous disks trail long stringers that are used to capture and immobilize its prey. But the stingers that deliver lethal injections to small prey also cause mild to severe skin irritation to those bold or foolish enough to enter the water when these strange creatures bloom.






University of Maryland, Horn Point


Sea Nettles, Chrysaora quinquecirrha, are a type of jellyfish found in the brackish regions of the Chesapeake Bay. They do not survive in the full salinity of the open ocean or in the fresh water of rivers and lakes. But where the two regions meet and saline water and fresh water mix to create the brackish water their bodies require, they bloom in prodigious numbers. The Chesapeake Bay is an ideal home for these languid hunters. Each summer they begin to appear in their adult form around late June with a maximum density and coverage in August and then decline in September.

Both the temperature and the salinity must match their requirements to support a large population. Annual variations in the climate can lead to large differences in the density and distribution of the sea nettles. These changes are tracked by the State of Maryland, giving swimmers and kayakers an opportunity to avoid these creatures if they desire. (Sea Nettle Forecast) Wet springs help to keep the population down. Attempts by man to reduce their numbers have proven ineffective. Nets clog, bubble curtains break them into small pieces that still continue to sting. Chemicals effective at killing sea nettles killed many other species as well. A sea slug that ate sea nettle polyps could not survive the fresh water environment that the polyps prefer.

Like all jellyfish, sea nettles have umbrella shaped bodies, stinging tentacles and oral arms that eat the prey captured by their tentacles. But perhaps captured is too active a word. Encountered may be more appropriate. Sea Nettles are weak swimmers, moving slowly up and down through the water column by pulsing their umbrella. Otherwise they are at the mercy of the currents and tides, drifting back and forth as the water responds to the tug of tidal forces and the wind.

But it is a good design. These simple creatures have been around for 650 million years. With no bones, no heart, no brain and no eyes, they are 95% water, 3-4% salt and 1-2% protein. With so little content, they appeal to few predators. They eat almost anything small that blunders into them; small fish, shellfish larvae, zooplankton and comb jellies. They breathe using their entire surface to absorb oxygen and release carbon dioxide. As they are mostly water, they can grow very quickly from the microscopic larvae to a 5 foot long adult.




Armed with up to two dozen tentacles, these trailing filaments have rows of stinging cells called Cnidocytes. These cells have both a trigger and a tensioned barb called a nematocyst. When contacted, the barb thrusts out and venom is released. What for most people is a minor skin irritation is a fatal result for small creatures floating by.

If you are stung, apply 70% isopropyl alcohol solution to disable the stinging cells or baby powder to dry them. Remove the tentacles that remain and then apply household vinegar. Meat tenderizer will help to break down the protein of the stinger toxin. If pain or swelling becomes worse, it's a good idea to seek medical attention. Some people are allergic to jellyfish stings and can develop allergic reactions. These can be particularly dangerous if stung in a central or sensitive area.

Turtles are one of the few threats to the jellyfish, at least in their mature phase. Loggerhead turtles, in particular, are fond of sea nettles and feed voraciously on them. Unfortunately for the turtles, they also sometimes mistake floating plastic bags for jellyfish with fatal consequences when they devour this carelessly discarded trash.




Adult sea nettles spawn in late summer. Males release sperm into the water and females are fertilized by the water they pump through their bodies. They then die after spawning, which accounts for the abrupt decline in adult numbers at the end of summer. The female releases larvae known as planulae. These float in the biological soup of the Bay waters, being eaten by other creatures including other sea nettles. After floating around for a few days, the larvae locate a hard surface and glue themselves to it. Anything hard and above the sand or mud will do, rocks, cans, bottles, oyster shells or dock pilings. Once attached they transform into flower shaped polyps.

In the spring, as temperatures rise, the polyps once again change shape. They become a series of stacked discs, Each stacked disc breaks off to become tiny "ephra". These microscopic sea nettles float in small streams and creeks during April and May. As they grow they move into the larger tributaries and out into the Bay itself. Then the cycle repeats.

Although they are considered a large nuisance by most people as they deny swimmers the water during the hottest portions of a Chesapeake summer, they are not without some beneficial uses. Because they eat so many comb jellies, which eat oyster larvae in large quantities, the sea nettle may be instrumental in any comeback for the Bay's endangered oyster population. So, in the right light, sea nettles can be beautiful.




Pictures of Jellyfish

Bioluminesence


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