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Volume 38 Issue 18 • Aug 28-Sept 3, 2008
now in our 38th season

Floating Wonders

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

As the summer temperatures warm up our harbor and offshore waters, floating translucent creatures begin to crowd our shores and worry swimmers.  Unfortunately, as ocean waters warm world-wide and we continue to over-fish or endanger their natural predators, the occurrence and number of jellyfish are on the rise.  Fortunately, our colder waters keep many of the extremely painful species relatively far from our beaches, although a few interlopers sneak in.  Jellyfish are the most primitive of the multicellular organisms. Although they can “swim” or move under their own power in a form of locomotion, they are more influenced by tides and currents and therefore are often still stinging capsules contained within cells called cnidocytes located along the tentacles.  These cells act as a trigger with a toxin bullet inside the cnidocyte. Thankfully, many of the smaller species cannot pierce human skin or produce enough of a sting to affect us. They concentrate their stunning power on smaller fish, plankton, and sometimes each other. In a way, jellyfish can “hunt,” feeling their way along the ocean currents, using rudimentary light and pressure sensors to detect victims, and silently dispatching their dinners.  Typically only when they become a nuisance or a danger do we become aware of them.

Jellyfish are invertebrate (no backbone) animals in the phylum Cnidaria in the family Medusae.  There are four major groups of cnidarians: Anthozoa, which includes true corals, anemones, and sea pens; Cubozoa, the amazing box jellies with complex eyes and potent toxins; Hydrozoa, the most diverse group with siphonophores, hydroids, fire corals, and many medusae; and Scyphozoa, the true jellyfish.  Many cnidarians are gelatinous and all of them are radially symmetrical.  Radial symmetry aligns all the body parts around a main axis in a cylinder.  One significant feature of radial symmetry is that it allows an animal to confront their environment in numerous directions.  A radially-symmetrical animal has no front or back end.  This body form is most common in sessile and drifting species.  Jellyfish appeared in the oceans about 650 million years ago, before the dinosaurs.  Known for being squishy, not  bony, few jellyfish have been preserved as fossils.  Jellyfish are made up of 95% water; they have no bones or cartilage, no heart or blood, and no brain!  Now you know what to call your little brother or sister.

In a rare occurrence in the summer of 2006, hundreds of Portuguese man-of-war (also spelled man o’war) jellyfish (Physalia physalia) showed up on southern Nantucket beaches, which prompted the temporary closing of many popular swimming beaches.  Although a few individuals can float into our waters, such a large influx can usually be contributed to a shift in the Gulf Stream.  Man-of-wars have a multicolored balloonlike float with tentacles that can hang down to 50 feet.  Portuguese man-of-wars are not jellyfish, but instead are a colonial animal composed of polyps and medusoid individuals called a siphonophore (Order Siphonophora) and are a member of the hydrozoa, or hydroid class. According to the Britannica Concise Encyclopedia, the medusa-form body consists of a translucent, jellylike, gas-filled float, which may be 3 to 12 inches long.  Polyps beneath the float trail tentacles up to 165 feet long.  Nematocysts on some polyps paralyze fish and other prey.  Other polyps then attach to, spread over, and digest the victim.  The Portuguese Man O' War (named caravela-portuguesa in Portuguese) is named for its air bladder, which looks similar to the sails of the Portuguese fighting ship (Man of war) Caravela redonda of the 14th and 15th centuries.  Man o’ wars can deliver a very serious sting and it is not uncommon to have the tentacles wrap around your entire body.  Some kinds of jellyfish and the siphonophore Man o’war can also still sting while washed up on shore because the nematocyst “trigger” has not fired yet; so be sure to avoid them (dead or alive).

Moon jellies (Aurelia aurita) are the most common member of the jellyfish family seen around Nantucket and on North Atlantic shores.  Moon jellies are translucent with 4 pink horseshoe-shaped gonads on the dorsal (top) of the creature and very short tentacles. Moon jellies are relatively small and do not sting humans.  The threadlike tentacles around the edge of the bell can sting, and may occasionally catch small swimming animals for food, but their stings — like minute harpoons fired by springs — are not powerful enough to pierce our thick skin.  They feed mostly by trapping microscopic plankton in a film of mucus which flows over the surface of the bell and is picked off as it reaches the edges by the thick mouth tentacles underneath.  They swim by pulsing their bell, pushing themselves slowly through the water.

Occasionally our surrounding waters may contain lion’s mane (Cyanea capillata) and stinging sea nettles (Chrysaora quinquecirrha), both of which are true jellyfish.  The lion’s mane jellyfish is the largest known jellyfish species and prefers colder waters.  The largest recorded specimen had a bell (body) diameter of 2.3 m (7 feet 6 inches) and tentacles 36.5 m (120 feet) long! It was found washed up on the shore of Massachusetts Bay in 1870.  Locally, the juvenile lion’s manes show up in late spring and are too small to really bother swimmers; they grow larger and less common throughout the summer and reach a typical bell size of 12 inches.  The lion’s mane starts as a pinkish juvenile and their color deepens to a purple or red as they age, although some smaller adult individuals are light orange or brown.  The bell is divided into eight lobes, giving it the appearance of an eight-pointed star.  A tangled arrangement of colorful arms emanates from the center of the bell, much shorter than the silvery, thin tentacles which emanate from the bell's subumbrella.  These jellyfish are understandably named for their showy, trailing tentacles reminiscent of a lion's mane.  The lion’s mane sting is moderately painful and sometimes feels like a burn.  It is important to note that while jellyfish stings can be excruciating, they are rarely serious health threats unless one is allergic to them. 

The sea nettle looks very much like lion’s mane.  This jellyfish is saucer-shaped with brown or red pigments, usually 6-8 inches in diameter.  Four oral arms and long marginal tentacles hang from the bell and can extend several feet.  Considered moderate to severe, symptoms from sea nettle stings are similar to those of the lion’s mane.

My favorite jellyfish-like creature is the comb jelly, which is not a jellyfish at all, but instead a member of the ctenophora (pronounced “teen o four a”) phylum.  Comb jellies differ from jellyfish in that they have 8 rows of comb-like cilia (“tiny hairs”) which are paddle-like structures that beat in the water to aid in orientation and locomotion.  Comb jellies also have biradial symmetry.  Comb jellies do not sting!  These little guys are delightful creatures also called “sea snot,” the reason for which will become abundantly clear if you ever hold one in your hand.  They are quite beautiful in the daytime with the cilia pulsing and scattering light producing a rainbow type effect, and they are even more beautiful at night because they produce a green light using chemical reactions in a process called bioluminescence.

This summer, our most common comb jelly, the Leidy’s comb jelly (Mnemiopsis leidyi, also known as the sea walnut), arrived even sooner than usual. Unfortunately, a large influx of Leidy’s comb jellies have been causing a significant food chain collapse in the Black Sea as they out compete fish for food items such as zooplankton.  The comb jellies and other jellyfish have an advantage over the visual hunters, like fish, as the waters in our seas and harbors become eutrophic (plankton-laden) and light penetration decreases; remember that jellyfish “hunt” tactically, so the lack of light is less of a problem for them.  In the warm waters of the Black sea, these ravenous carnivores eat the zooplankton before the fish eggs can hatch and the larval fish species can begin to eat.  These comb jellies came over as an invasive non-native organism in the early 1980’s in ship ballast water.  Currently, the only option for fighting these is the introduction of a different comb jelly species, Beroe ovata, which is a predator of the Leidy’s comb jelly. Some of the Black Sea fisheries are beginning to rebound as the Leidy’s comb jelly population decreases.

Jellyfish are a favorite menu item for many sea turtles, which is why the abundance of balloons and plastic bags floating in the ocean have found there (sometimes lethal) way into a turtle’s stomach.  One of the largest sea turtles species, the leatherback, consumes jellyfish almost exclusively.  Ocean sunfish (mola mola), some tuna and shark species, and ocean birds such as fulmars and phalaropes also eat jellyfish and are immune to their toxins.  Jellyfish are also on our dinner plate in popular Japanese and Chinese dishes. I’ve had it once and survived (it was actually quite good, a cold pickled salad).

Remedies for jellyfish stings include applying a cold pack or ice to slow the spread of toxin or applying hot water to break down the toxins.  You can also treat a sting by removing the barbs if they can be seen and then cleaning the area with rubbing alcohol, ammonia, vinegar or urine (yes, you read right). While working the Portuguese Man O’ War dense waters off of Galveston, I usually carried a container of Adolph’s meat tenderizer which contains an enzyme similar to papain to break down the proteins in the toxins.

There are many great websites about jellyfish and their gelatinous cousins. To learn more try, which is a fun site with lots of great pictures.  Although based more on Pacific organisms, you’ll find plenty of information there.  I also liked University of Washington biologist Claudia E. Mills’ website:

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