Sea nettle photo by Mary Hollinger, NOAA
Each summer, a small creature appears to silently haunt the Chesapeake Bay. So intimidating is this little animal that even the hardiest souls won't enter the water. No it’s not a shark or some other fearsome predator. It is the sea nettle (Chrysaora quinquecirrha) whose graceful, gelatinous body keeps us onshore not wanting to risk its inevitable sting.
A member of the jellyfish family, the sea nettle is actually a year-round resident. Before taking on the distinctive umbrella shape, sea nettles go through a variety of growth stages, which are not recognizable or cannot be seen with the naked eye. It is only the adult "medusa" form we are all too familiar with.
Nettles' movements are predominately driven by wind, tides and currents. By contracting and relaxing its body, the sea nettle can, however, produce weak swimming motions.
Because of their preference for brackish to salty water, sea nettles are usually found in greater numbers in the mid or lower Bay regions. Adult sea nettles favor warmer water temperatures too. Unusually hot, dry summers will produce larger nettle populations and increase their range into the upper Bay.
The body of an adult nettle consists of a white umbrella-shaped "head," oral arms which can digest and move prey toward the mouth, and 8 to 24 tentacles which may be 4-5 feet long. Each tentacle is armed with stinging cells called nematocysts. Each nematocyst contains a trigger and a venomous barb, similar to a hypodermic needle.
Sea nettles eat small fish, shellfish larvae, worms, zooplankton, and even other types of jellyfish. Prey becomes entangled in the sea nettle's tentacles. When touched, the stinging cells shoot the barb to sting the unwary with a potent poison.
Once stung, prey is stunned and can be easily consumed. The mere design of the sea nettle makes it an extremely efficient hunter. Tentacles that are broken off are readily replaced by regeneration and even amputated tentacles retain their stinging abilities. Luckily for humans, a sea nettle sting causes only minor irritation to the skin.
Sea nettles have few enemies. Since body mass consists mostly of water, nettles are not much of a meal. Some species of sea turtles, however, do include sea nettles in their diet. One turtle in particular, the loggerhead turtle, feeds voraciously on sea nettles in the Bay.
Sea nettles and their relatives have existed on earth for nearly 1/4 billion years. Their life cycle is perfectly adapted for the estuarine environment of the Chesapeake Bay. Looking beyond the minor inconvenience of sea nettles, it's hard not to appreciate the prehistoric beauty and efficiency of these translucent creatures. For a short period in the summer, sea nettles rule the waters. Whether you admire or despise them, sea nettles are here to stay. To coexist, we need only to stay out of their way.