Jellyfish are transparent, somewhat spooky and drift through the world’s oceans like a crystal-clear air balloon with long strings attached. Don’t be fooled by their gelatinous or see-through appearance though, and believe they are weak. They are predators and live by snaring other fish into their stinging tentacles and sweeping plankton into their mouths. A few species such as the tropical box jellyfish are among the most venomous creatures on Earth with more poison than a cobra snake. The box jellyfish kills more people each year than any other marine animal.
Jellyfish have been floating in the world’s oceans for about 650 million years. Asian and Greek mythology often depicts jellyfish as repulsive. In fact, jellyfish may have influenced the story of Medusa (who transformed into an ugly creature with snakes for hair).
Some 200 species have a similar body composition: spineless—invertebrate—brainless, and living under a bell called a medusa, with tentacles hanging beneath.
Scientists often refer to them as “gelatinous zooplankton," or parasitic jellies. They can float along with the current or anchor themselves to the ocean floor. Some tentacles grow to enormous lengths. On the Portuguese man of war, they could stretch across a baseball field from home plate to almost second base at 165 feet (50 meters).
Even though they are made up of 95 percent water and transparent, perhaps in delicate or glowing colors, they are not overly fragile. These unique physical features allow them to weather extreme temperatures, acidity, salinity, light and darkness. One species can turn itself back into a polyp when injured, make copies of itself and revert back and forth, indefinitely.
Their locomotion and the ability to hunt plankton and tiny fish is accomplished by contracting the muscles around the rim and tossing stunned fish into a miniscule mouth. The jelly digests its prey in its body cavity and subsequently expels the remaining parts of the prey through the same single opening. Its’ efficient and capable adaptability let them respond to a simple nervous system, not a brain, called a nerve net. These receptors detect changes in light or temperature.
Their main defense is special stinging cells called “nematocysts." The tiny barbed darts are buried in their tentacles and with contact, can trigger thousands of stinging cells. Any fish or turtle that accidentally swims into their net are instantly harpooned—and the more thrashing, the more stinging darts. Generally, the only predators for them are seagulls, birds, some sea turtles and other jellyfish.
What is a Bloom?
A “bloom of jellyfish" is a seasonal abundance of a population increase due to reproduction or growth. Jellyfish blooms have closed beaches in the Mediterranean, clogged power plants in Sweden and halted fishing in Japan.
Gelatinous zooplankton group-blooms are deeply rooted in evolutionary time due to asexual propagation, which occurs in various modes. Some hermaphroditic ctenophores, or comb jellies, can self-fertilize, which means they can create rapid numbers of themselves during favorable conditions. That adaptable jellyfish can also lie on the ocean floor for years.
Blooms once occurred every 40 years. Now, with higher ocean temperatures, they occur much more frequently. In many parts of the ocean, high concentrations of agricultural nutrients cause plankton to grow explosively. This, in turn, depletes some areas of ocean oxygen, creating “dead zones." Most marine life can’t survive in an oxygen-deprived environment — except for jellyfish. They are commonly found in North Mediterranean climes, Northern Queensland and along Florida and Japanese coasts.
In recent years, Japan has been enduring what could be called this jellyfish-saturated vision of the future. Dead zones are almost doubling every decade, with 400 worldwide currently.
Massive blooms of Nomura’s jellyfish suddenly began occurring annually in Japan. Experts wondered if it was agricultural run-off from farming. Jellies have clogged fishing nets, devastated fisheries, harmed electricity plants and killed tourism. Common reasons for Japan’s problem ranged from overfishing, global warming, pollution, lower oxygen levels, toxic zones and nutrients for zooplankton.
Observational efforts in marine ecosystems have increased in the scientific community. Casual public observation has grown exponentially with the aid of social media. Some scientists believe these casual, anecdotal reports get an immediate global audience equivalent to that of a reputable news or science report and that the problem is overstated. They feel the presence of dense gelatinous zooplankton aggregations is not necessarily caused by an actual increase in numbers in a particular region, but that these abundant spikes may be localized and not representative of the entire region in question.
Nevertheless, Japanese scientists and entrepreneurs are scrambling for solutions. Killing the jellies just makes them release eggs, which, in turn, creates new spawning areas.
Not All Bad
Jellies are edible but not appealing to eat; Japanese chefs are looking for recipes to feature them. On the plus side, advances in medicine have occurred such as, a better understanding of anaphylaxis, as a luminous marker in cellular research, and with using jellyfish toxins for anticancer compounds. As a last resort, they could theoretically be reconstituted to fertilizer.
Jellyfish are also hosts for various other animals. The open-ocean ecosystem has a lack of physical refugia—a location that supports other lifeforms. In fact, the Portuguese man o’ war often harbors juvenile or small adult fish under their bell or among their tentacles—and this hiding place provides a haven from predation and gives them improved feeding opportunities. The fecal pellets of the jellies drop to the ocean’s bottom and supply carbon sequestration too, and may likely be a direct function of salp abundance (a form of plankton) in the oceans.
Tourists love them
The Island of Palau, home to the Mastigias population, draws 30,000 visitors annually to swim with the jellies; as well as scuba diving enthusiasts in the Sea of Japan. There is more revenue for popular aquaria with jellyfish; in 2012, Monterrey Bay Aquarium created a large scale, $3.5 million-dollar jellyfish exhibit.
A jellyfish economy may be the only way to balance out the negative impact of booming populations. One Japanese scientist is even building artificial reefs and stocking it with jellies, which the fish devour.
- King, David C. Jellyfish. Tarrytown, NY: Marshall Cavendish Benchmark, 2006. Book.
- JEDI, the Jellyfish Database Initiative
- JstorDaily: Global Jellyfish Crisis
- Jellyfish Watch.org: Blooms
- Wilcox, Christie. Venomous: How Earth’s Deadliest Creatures Mastered Biochemistry. NewYork: Scientific American| Farrar, Straus and Giroux, 2016. Book.
- Woodward, John. Look Closer Ocean: An amazing window on our world. London: Dorling Kindersley Limited, 2012. Book.