Mary Syrett - May 2011

 

Gelatinous Gems
by
Mary Syrett

Fascinating creatures with amazing adaptations, the Tidewater’s jellyfish are more than just stinging threats to swimmers. They are pulsating, gossamer jewels of the sea; brainless creatures; kings of sting; plankton drifters. There are more than 200 known species, and yet they remain phantoms to most people, including Atlantic Coast residents. They can live for one to ten years, depending on the species. The fragile, luminous beauty of jellyfish makes them a popular subject for underwater photographers. That they are variously known as edible delicacies, threats to fisheries, beach nuisances, household pets and dangerous killers adds all the more interest.
“Jellyfish” is the name given to any organism that is pelagic (lives in the open ocean), consists mostly of water and has a jelly-like consistency. Actually, jellyfish are not made of jelly at all. Their gelatinous appearance comes from protective skins filled with a substance that is approximately 95 percent water. Muscle fibers laced throughout the jellyfish’s strange body hold the creature together.
These creatures are not really “fish.” Rather, they are invertebrates that are related to sea anemones. A jelly has no head, brain, heart, eyes, ears or bones. But that’s no problem for them. Jellyfish might seem capable of melting away on a Maryland beach, but actually they’re not all that fragile. These marine organisms can, in fact, survive long sea journeys and considerable wave battering.
Jellyfish are marvelously well adapted to a drifting, predatory life in the ocean, gulf, sound, bay or saltwater inlet of any kind. Jellies get around by means of a unique pulsating action. Long ago, people called the creatures “sea lungs” because their rhythmic movements through water somewhat resemble human breathing patterns. Their habitat is usually coastal waters, but they also live in the open ocean as well as freshwater lakes and streams. Jellyfish drift individually dispersed, or in aggregations called “smacks” that are measured in acres and sometimes square miles.
Many of these creatures resemble floating mushrooms, with long tentacles reaching underwater like weeping willow branches. Most true jellyfish have brightly colored tentacles – elongated, flexible protrusions that contain poisonous, stinging cells known as nematocysts that can pierce the skin. Other creatures with nematocysts include sea wasps, anemones and fire corals. These stinging organs continue to function long after the animal has died.
The person who once described jellyfish as “little more than organized water” had his or her facts about right, but could have been a bit more positive about these fascinating creatures. Found in all the world’s oceans, jellies often are seen near the surface of the water during times of diminished light. Individuals range from fingernail-sized to creatures that would overflow a bushel basket.
Jellyfish can be useful. Some species are harvested and dried for human consumption, mainly in Asia. Many sea turtles feed heavily on jellyfish. Several fishes, including salmon, Atlantic mackerel and cod, also eat jellyfish.
Maryland’s Jellies
Jellyfish have long inspired individuals who have seen them up close in the wild. Explorer William Beebe, who in the early 1930s dived deeper than anyone ever had before, had great affection for the jellies that he saw and studied. In his book Nonsuch: Land of Water, Beebe describes a group of what are known as moon jellyfish: “I swiveled half a circle and entered a galaxy – an entire constellation of great jellyfish all around me. Moons they were, all more than a foot across throbbed around me, set at various angles, each with bright pink loops at its center – egg masses. There came to me a profound feeling of the permanence of the evanescent: these [creatures] filling the ocean in great numbers, each jelly perfect.”
The moon jellyfish is named for its moonlike shape and translucent white colors. Often found in enormous smacks, the moon is the jellyfish most commonly seen washed up on beaches. It thrives in Maryland waters from April to early November, depending on water temperature and currents.
The moon jellyfish has short, fine tentacles descending from the rim of its body. That body, known as an umbrella, may be as much as 18 inches across and gives the creature the appearance of a flying saucer. Visible on top of the moon’s umbrella are purple horseshoe shapes that are part of its reproductive system. Four frilly oral arms hang underneath its body, surrounding the mouth. The arms help manipulate food and serve as a home for developing larvae.
The sea nettle is about the same size as a moon jelly, but its umbrella may be ale white and resembles the spokes of a wheel. It is also found along the Maryland coast during the summer months.
The mushroom jellyfish is found in Maryland waters between July and November and occasionally enters sounds and estuaries. The mushroom can grow as large as 14 inches in diameter and is quite fragile, breaking easily if lifted out of the water. It has no tentacles on its umbrella. Instead, its fingerlike oral arms extend down from the center of its umbrella and contain hairlike cilia that sweep plankton into its mouth.
Have you ever thought about eating a peanut butter and jellyfish sandwich? The cabbage head jelly is a popular menu item in parts of the world. According to some people, the cabbage head is not only delicious, but also low in fat and calories. Other diners claim it tastes remarkably like rubber. The cabbage head is also known as the cannonball or jellybomb.
Like the mushroom, it has no tentacles. Its short oral arms extend just below the edge of its umbrella, which reaches 8 to 10 inches in diameter and is bordered with brown pigment. It is abundant during summer in both Maryland sounds and ocean waters.
Not only is the lion’s mane jelly famed as the world’s largest jellyfish (its bell can measure eight feet across and its tentacles reach lengths of 100 feet), but the creature played a role as the villain in Sir Arthur Conan Doyle’s Sherlock Holmes story The Adventures of the Lion’s Mane. Luckily for swimmers stung by this creature, outside the pages of Doyle’s tale, death rarely results. The lion’s mane, which feeds on plankton, fish and moon jellyfish, is found around the Tidewater from October to May.
When are jellies not really jellyfish at all? When they’re comb jellies. These creatures are distantly related to true jellies and have a solid, egg-like body rather than a bell and tentacles. Unlike their pulsating cousins, comb jellies use their rows of cilia – microscopic hairlike features that resemble tiny combs – to paddle through water and move food towards the mouth.
The much-feared Portuguese man-of-war is not a true jellyfish, but a colony of specialized creatures related to the fire coral. It is a gas-filled floating bladder that supports three types of polyps, each with a different function – sensing and capturing prey, feeding and reproduction. The polyps trail tentacles that may be as long as 150 feet. Strong winds may blow the man-of-war inshore in summer and early fall.
Jellies as Pets
These marine organisms are among the most fascinating creatures of the sea. It’s little wonder, then, that many public aquariums display jellies. Likewise, some hobbyists envision a home aquarium filled with glowing gelatinous orbs.
This is a more difficult proposition than one might imagine. There are dozens of ways to accidentally kill captive jellyfish, and a strict set of guidelines for keeping them alive. Anyone who wants to keep jellyfish in his home would be well advised to research the topic thoroughly.
That said, the moon jelly is perhaps the easiest species to maintain. Primarily a cold-water species, moons do best at the low end of room temperature. If your home is located in a fairly cool clime, or is air-conditioned during the summer, these creatures generally can survive.
The chief obstacle facing a person who is considering a jellyfish aquarium involves obtaining them. With a few exceptions, you can forget about purchasing jellies from a tropical fish dealer. You may possibly encounter several species for sale at well-stocked aquarium shops.
With a boat and the proper tools, you can collect jellies from the ocean. Timing is important. Jellyfish are notorious transients – present in hordes one day, gone the next. A collector can never be certain that jellies will be seen on an ocean excursion. If you can’t get out in a boat, you will sometimes find jellies drifting in waters that surround harbor docks.
Once spotted, small jellyfish are usually not too difficult to capture. It is important to keep jellyfish supported in water at all times – collecting with a net or any other method that takes away water support, even if only briefly, may severely damage delicate jellyfish. If not done exactly right, they collapse into a gelatinous glob that may not recover when returned to a suitable aqueous environment. The ideal way to collect is to gently scoop the creature from the sea into a water-filled jar.
Cups, beakers, strong plastic bags or buckets can all be used if you surround a jelly with the container and then slowly lift it out of the water. This is easier to accomplish when a jellyfish is on the surface. After collection, the animal can be placed in a large container.
Aquarium Setup and Feeding
Successfully maintaining captive jellies requires abandoning preconceived ideas you may have about keeping fish. If you had a tank with limitless volume and no solid boundaries, you would have an ideal environment for jellyfish. However, only an ocean can meet this lofty ideal.
Several tank system designs have been developed that enable some species of jellies to thrive in captivity. A key concept in such designs is to have incoming water directed across a screen through which the water exits the tank. This provides a circular flow that keeps jellyfish suspended and allows water to move without a pump sucking them up and killing them.
What does an aquarium enthusiast feed captive jellies? Jellyfish are predators that require live prey. Brine shrimp are best for speeding growth and prolonging life. Krill, an abundant group of crustaceans found in cool water, is also an excellent food source.
Jellyfish are a marvel of the animal kingdom. Amazing denizens of a watery world, jellyfish are unmatched in style and beauty when viewed in their natural habitat, or in a properly set up home aquarium. With care, jellyfish can bring endless hours of fascination and enjoyment to you and your family. Enjoy, but be careful when exploring around tidal waters.
A Key Question:
How Do Jellyfish Navigate Without Brains?
Jellyfish are primitive creatures with simple nervous systems. Nonetheless, they do have sensory organs that help them find the essentials of life. Jellies are “eight-fold symmetrical,” meaning that sense organs ring their bodies.
Jellyfish have groups of light-sensitive cells called ocelli along the edge of their bells. Ocelli don’t form images but can detect light and shadow, as well as day and night. Depending on what the animal needs at a particular moment, it moves toward or away from the lighted side.
Jellyfish capture prey using nematocysts, which are cells containing tiny venomous darts. Cells alongside the nematocysts can detect the scent of prey and trigger the darts. These cells can also detect prey some distance away; consequently, the animal swims toward the side that receives a scent.
To orient themselves in the natural world, jellyfish need to know up from down; organs called statocysts allow them to do that. A statocyst is a hollow ball of sensory cells with a tiny mineral particle, called a statolith, trapped inside. Gravity continually pulls the statolith down, which action stimulates the sensory cells it contacts, informing the jelly of its vertical orientation. Primitive creatures? You decide.

Mary Syrett is a freelance writer and an avid student of nature.