In the summer months, jellyfish mysteriously arrive by the thousands in the Chesapeake Bay and its tributaries. These lucid creatures appear to be drifting along aimlessly, a mass infiltration of jelly-filled blobs. From May through September they are present in the waters of the lower and middle Bay, but seem to surge during July and August. Why are they so abundant and is there something unique about their nature that sets them apart from other species in our waters?
The appearance of jellyfish makes us second guess ourselves before diving in on a hot, summer day. Local residents share tales of skiing in turtlenecks and jeans or wearing lycra hose under swimsuits just to avoid a potential sting. There have even been attempts to diminish their populations in certain areas. Consequently, other marine life suffered.
The painful truth about jellyfish is that they are most likely here to stay based on how well-adapted they are for their way of life. In recent years, “fossil snapshots” have been discovered in rocks over 500 million years old that exhibit characteristics relating to modern day jellies. The more we study them, the more we will understand why they are one of nature’s great survival stories.
The word “jellyfish” is a misnomer, for they are not fish at all. Moving primarily by drifting, they are the largest type of floating zooplankton, or animal plankton. Though they are not strong swimmers, they can propel themselves by contracting and expanding their umbrella-shaped bell. Mostly they rely on the tides and currents for transportation.
Jellyfish have no brain. Instead they have an elementary nervous system with receptors for detecting light, vibrations, and certain chemicals in the water. These senses, combined with a feeling of gravity, give the animal the ability to guide itself.
The Stinging Variety
Jellyfish that sting are members of the phylum Cnidaria (from the Greek word for “stinging nettle”), and of the class Scyphozoa. The mature form of the jellyfish, with its bell and tentacles, is known as “medusae,” appropriately named for Neptune’s serpent-haired wife. Covering the tentacles are specialized stinging cells. Inside the cells (cnidoblasts) are capsules, or nematocysts, each containing a coiled up thread lined with barbs. A single tentacle can have hundreds or thousands of nematocysts. These cells are like “spring-loaded harpoons” that release venom once the jellyfish senses touch.
Simple animals, jellyfish are made up of two cell layers, the epidermis (“outer skin”) and the gastrodermis which lines the gut. In between is a thick, non-living non-cellular layer called the mesoglea (“middle jelly”). On the underside of the jellyfish’s body is an opening serving a dual fold purpose: to eat and expel waste.
In the Chesapeake Bay there are three types of jellyfish that are common: the moon jelly (Aurelia aurita), the lion’s mane (Cyanea capillata), and the sea nettle (Chrysaora quinquecirrha). The largest is the moon jellyfish, which can grow up to one foot. It has a transparent, flat disk with a four-leaf clover design (reproductive organs) visible through the bell. With its shorter tentacles, the moon jelly delivers a very mild sting.
Fortunately for swimmers, the lion’s mane, another of the stinging varieties, is not present during the summer months. Rather, it is present in Tidewater Virginia during winter and spring. It is orange-brown in color with relatively short tentacles. Often, masses of these jellyfish drift into in fishermen’s nets, getting tangled and adding weight as they are dragged into boats.
By far the most well known of the Bay jellies is the sea nettle, often referred to as the stinging nettle. In the middle Bay and its tributaries, stinging nettles can be identified by their milky white color while in the lower Bay they are characterized by red/maroon markings. Hanging from the center are four oral arms used for passing food to the mouth. Their tentacles can trail several feet, so keep your distance!
Diet and Food Web
Stinging nettles usually grow to 6–8 inches in diameter and are voracious predators. Carnivorous, they feed continuously on zooplankton, but also eat bay anchovy eggs, worms, and young minnows. Jellyfish will paralyze their prey with poisonous venom once it becomes entangled in their tentacles, making it easy for them to consume.
Even though they can be found as far north as Cape Cod and as far south as the Caribbean and Gulf of Mexico, stinging nettles are most concentrated in the Chesapeake Bay. An estuary rich in plankton, the Bay is full of copepods (small crustaceans) and comb jellies— jellyfish favorites. As part of the food web, they help to keep smaller crustacean zooplankton populations “in check,” as well as help control the comb jelly population in the Bay.
Made up of 90% water, a jellyfish is no more than a morsel for most fish; however, spadefish, butterfish, sea turtles, spider crabs and other jelly plankton depend upon it for food. Some of these species have formed symbiotic relationships; for example the butterfish, are immune to the venom in the stinging cells and can therefore swim in and out of its tentacles. Furthermore, the spider crab will sometimes “hitch a ride” by burrowing in the top of the medusae’s bell.
Where do stinging nettles go in the fall? Once they have spawned in mid-late summer, they die. Fertilization occurs when the male releases sperm into the water (broadcast spawning). Once the sperm enters the stomach cavity of the female, the egg is fertilized and a tiny planula larva forms. The pinhead sized larva drifts along with other plankton before sinking to the bottom, cementing itself to a hard surface, such as an oyster shell or a rock. The larva then becomes a polyp, a hollow cylinder with a mouth and tentacles at the top.
As the water warms, the polyp begins to double itself over and over, resembling a stack of saucers. During this process, known as strobilization, a tiny medusa is formed (ephrya). The ephrya wriggles free from the polyp and finds a home in smaller creeks.
Strangely enough, the life cycle of the stinging nettle includes two very different body forms as well as a sexual stage and an asexual stage. This phenomenon is known as “alternation of generations.” By early summer, the ephryae migrate into the open waters of the Bay to feed on plankton. The more they food they consume, the more they will grow throughout their lives.
What conditions are ideal for jellyfish? Warm water temperatures combined with dry conditions and an abundance of food, are factors that contribute to the growth of jellyfish. Able to survive in waters of lower salinity (10–16ppt), but not fresh water, stinging nettles are more prevalent in the Bay and its rivers when temperatures range between 78–86 degrees.
Recently, scientists developed an experimental model for predicting nettles. By taking satellite images and gathering salinity and water temperature readings, real-time maps are created showing probable areas for nettles along the East Coast. Before taking a dip in the river, you can refer to a map of nettle distribution for your region on NOAA’s Chesapeake Bay Office website: www.chesapeakebay.noaa.gov.
Treating a Jellyfish Sting
The severity of a jellyfish sting varies with the species, and the sting of the Chrysaora is considered moderate to severe. The stinging sensation differs from person to person depending on the location of the sting and the person’s sensitivity to the venom. When we get stung it is likely that the jellyfish thinks of us as a meal swimming into its tentacles. Dr. Deborah Steinberg professor at VA Institute of Marine Science notes, “It is not clear how much stinging is used as a defense, as this is very hard to distinguish from prey capture.”
Should you get zapped by a stinging nettle, there are a few steps you should take. First carefully remove the tentacles from the skin by scraping the affected area with a clam shell, credit card, sand, towels, or any other available material. In a pinch, you can then coat the area with a paste of salt water mixed with sand or mud.
There are many home remedies and store bought ones that you can try as well that help to alleviate the pain. Dr. Steinberg, suggests keeping a container of unseasoned meat tenderizer in your beach bag for emergencies and making a paste with it. It can be applied a few times, but be careful not to exceed 15 minutes. If vinegar or baking soda is available, apply liberally until the pain is relieved. Baking soda can be mixed with sea water to make a paste. Warning: In the case that an allergic reaction occurs, seek help from a doctor. Be careful not to rinse the affected area with fresh water, as the stinging cells may continue to fire. Also remember that beached jellyfish may still have active stingers.
Thin lycra suits and rash guards can be effective in protecting against stings, as the barbs of a stinging nettle can not penetrate these fabrics. In fact, the skin in the palm of the hand is too thick for a nettle’s stingers to penetrate. Furthermore, rubbing a layer of petroleum jelly on your skin may help. There are also sting inhibitor creams such as “Safe Sea” on the market that contain clown fish mucous. This may sound gross, but if you’ve watched “Finding Nemo,” you might remember that Nemo’s parents lived inside of a sea anemone for protection.
Comb Jellies and Stinging Jellies—Are they Related?
Many of us have witnessed a glowing light in the wake behind our boats at night or flashes of green as our canoe paddle slaps the water. These bioluminescent creatures are known as comb jellies, from the Phylum, Ctenophora. Found in most marine habitats from polar to tropical, there may be as many as 150 species of Ctenophores throughout the world’s oceans.
Ctenophores are present in the Chesapeake Bay throughout the year. In spring and summer, they thrive and overall are much more abundant than other jellyfish. Bearing eight rows of cillia used for movement, Ctenophores (Greek for “comb-bearers”) propel themselves by beating their bright rainbow colored rows of combs against the water. Two varieties that are commonly seen in the Bay are the sea walnut (Mnemiopsis leidyi) and the pink comb jelly or rainbow jelly (Beroe ovata).
Although Ctenophores do not have nematocysts like the Cnidarians, certain varieties have colloblasts, which are sticky cells used to ensnare their prey. Other varieties capture their prey using a pair of oral lobes coated with a sticky mucous.
Medusaes and comb jellies have many similarities, but also several distinctions. They are similar in that they both are copepod feeders, are carnivorous, are mostly composed of water; and exhibit radial symmetry (body parts are arranged around a central axis).
One significant difference between the medusaes and the comb jellies is their method of reproduction. Comb jellies are hermaphroditic and capable of self-fertilization. They are able to produce many generations of offspring in a single summer. If you would like to view one of these delicate little creatures up close, try scooping it up in a glass container.
Generally speaking worldwide, the jellyfish population is increasing. Their growing numbers may be an indication of what the future holds for fish populations. A press release from VIMS reports “the increase in frequency of jellyfish blooms in coastal and estuarine waters around the world during the last few decades means that jellies’ impact on marine food webs is likely to increase into the future.” These findings are the result of a recent collaborative study led by VIMS Ph.D. Graduate, Rob Condon, using jellyfish bloom samples in the York River.
Condon states, “Jellyfish impact food webs by capturing plankton that would otherwise be eaten by fish and converting that food energy into gelatinous biomass. This restricts the transfer of energy up the food chain, because jellyfish are not readily consumed by other predators.” In other words, food energy gets taken away from fish and shell-fish. Other factors in the environment influence the frequency of jellyfish blooms such as weather patterns, climate change, over-harvesting of fish, and fertilizer runoff.
Some scientists believe that the increase of jellyfish worldwide can be interpreted as a decline in the overall health of the sea. Pollution, which depletes oxygen in our waters, over-fishing, and overall warming of the waters are all factors that may be fueling the population of these durable little creatures.
A special thanks to Kevin Goff, Ph.D. Student, W&M School of Education, and Dr. Deborah Steinberg, Professor of Marine Science at VIMS for providing assistance and resources.