Island Science

Dangerous Beauties – Jellyfish

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 become a concern for 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 almost planktonic in their motions.

They are famous for their beautiful transcendent appearance in aquariums and infamous for their stinging capsules contained within cells called cnidocytes located along the tentacles.  These cells act as a trigger with a toxin bullet composed of a protein-based venom inside the cnidocyte. A cnidocyte fires a structure that contains the toxin, from a sub-cellular organelle called a cnidocyst (also known as a cnida (Latin for nettle) or nematocyst). This is responsible for the stings delivered by jellyfish. This acts as a one shot harpoon that literally embeds itself within tissue. Knowing that this chemical is protein based is helpful for counteracting it; when I worked in Galveston Bay (which was basically jellyfish heaven), we always carried Adolph’s meat tenderizer or some type of papain based spice to help break down the proteins in the stinging cells. But nowadays the old standby treatments like ammonia, vinegar, meat tenderizer, and urine are not considered nearly as effective as hot water (not that anyone has that on them) or lidocaine or other topical anesthetics accessed August 6th 2012. I would always recommend using salt water to wash off the stinging cells, not fresh water.

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 (next week, on the Animal Planet, Jellyfish Wars!). 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 true 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 (the name “Man of War” now starts to make sense) or “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. Although they are diminutive in stature, they have no Napoleon complexes that have been recorded and do not have a painful sting.  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 pulsating their bell, pushing themselves slowly through the water. This Youtube video does a great job of showing you how they propel themselves along

Occasionally our surrounding waters may contain lion’s mane (Cyanea capillata) and stinging sea nettles (Chrysaora quinquecirrha), both of which are true jellyfish.  The sea nettle has been the prime offender the past two weeks and has been encountered in Monomoy and on some of our island beaches.

The Mayo Clinic recommends a three-step process for treating sea nettle jellyfish stings (my notes are in brackets).

  • “First wash off the sting area immediately with seawater to remove any remaining tentacles. Be sure to use seawater; using fresh water can cause more stings to occur.” [This is crucial advice for most jellyfish stings].
  • “Don’t use vinegar for sea nettle stings, it can cause any remaining nematocysts to fire.” [The use of vinegar for jellyfish stings has fallen out of favor and hot water around 120 degrees or so is recommended instead.]
  • “Secondly, remove leftover stingers by applying shaving cream or a paste of seawater and baking soda or sea water and talcum powder to the sting area. Scrape it off when it dries.” [If you have to remove the nematocysts manually, wear gloves or use a stick to lift them off].
  • “Lastly, relieve the pain and itching with ice and over-the-counter skin creams (such as calamine lotion).  Rinsing or soaking the sting area with hot water may also help.” [Ibuprofen or other pain relievers will diminish the inflammation]. accessed August 5th, 2012.

The lion’s mane jellyfish is the largest known jellyfish species and prefers colder waters.  You may remember this jellyfish from the Sir Arthur Conan Doyle Sherlock Holmes story “”The Adventure of the Lion’s Mane”. 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.

As mentioned above, I have received a few reports over the past two weeks of sea nettles along the north shore and in Monomoy. 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. The bell area can be a milky white color.  Four oral arms and long marginal tentacles hang from the bell and may extend several feet. The arms are wavy and very pretty almost like cellophane. Considered moderate to severe, symptoms from sea nettle stings are similar to those of the lion’s mane.  Sea nettles spawn in mid to late summer and they usually die after spawning. First the males release sperm into the water, then the females’ eggs are fertilized as they swim and pump water through their body. Not the world’s most efficient process, but whatever floats your boat. After fertilization, the eggs develop into tiny, free-swimming larvae called planulae, which the female releases into the water. The larvae float with the currents for a few days, then settle and attach to a firm surface. The larvae blossom into anemone-like polyps that bud and grow over the winter.  By spring, the polyps develop tiny, floating medusae that are layered on top of one another. The medusae are eventually released into the water. The freely floating medusae (called ephyra) eventually grow tentacles and mature into adults. One of the key steps is the attachment of the larvae and the increase of hard surfaces like bulkheads and docks has been blamed for an increase in jellyfish populations in some embayments. The Barnegat Bay Partnership in New Jersey has even begun to experiment with a net system to keep stinging sea nettles away from swimmers (more info at accessed August 5th, 2012). Other factors like excess nutrients, warming waters, and a reduction in their natural predators likely play a large part in ballooning jellyfish populations.

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. They are commonly confused with jellyfish. 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 that causes these creatures to flash on and off when disturbed. You can see this light show on dark nights in the harbor especially near the Head of the Harbor and off Steps Beach. When we did a recent marine biology tow (end of July) our plankton net filled up with comb jellies in just a few seconds. The comb jelly most commonly found on Nantucket is the Leidy’s comb jelly (Mnemiopsis leidyi) also known as a sea walnut which is a staple food item for sunfish, turtles and other sea creatures.

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 hyper-eutrophic (excessively high nutrient concentration which causes water to become 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. Fortunately, parts of the Black Sea fisheries are beginning to rebound as the Leidy’s comb jelly population decreases.

Hopefully you are avoiding the jellyfish out there! Next week we’ll talk about biomimicry and perhaps explore some ways in which jellyfish are able to teach us how to design things from weapons to lights. Portions of this article were originally written in an article in the summer of 2008 which can be found at

Articles by Date from 2012