JELLY PACK: A bloom of moon jellyfish, which get their name from their circular shape

©MATHIEU FOULQUIÈ/BIOSPHOTO

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Jellyfish Invasion!

Are people to blame for a growing number of jellyfish swarming the seas?

May 13, 2019

By Andrew Klein

ESSENTIAL QUESTION: What factors might cause a population of organisms to suddenly increase?

What should have been a fun trip to the beach last June soon turned into a nightmare for thousands of visitors to Florida’s eastern coast. Over the course of two weeks, more than 3,000 beachgoers were stung by nettle and moon jellyfish. Luckily, no one was seriously injured. Although stings from these types of jellies can be extremely painful, they’re rarely deadly.

Last June, visitors flocked to Florida’s eastern coast. It should have been a fun trip to the beach. But it soon turned into a nightmare for thousands of people. More than 3,000 visitors were stung by nettle and moon jellyfish over a two-week period. Luckily, no one was seriously hurt. Stings from these types of jellies can be extremely painful, but they’re rarely deadly.

JELLYFISH SIGHTINGS

This map shows areas with increased sightings of jellyfish blooms, represented by red triangles and blue squares. Scientists are uncertain whether more blooms are in fact occurring or if people are just better at reporting them than in the past.

JELLYFISH SIGHTINGS

This is just one recent encounter between people and swarms of jellyfish, called blooms, in the worlds’ oceans. Reports of these incidents have been on the rise for the past few decades (see Jellyfish Sightings). Jellyfish blooms can cover thousands of square miles and cause all sorts of trouble. In places like Israel, Japan, the Philippines, Scotland, Sweden, and the U.S., the gelatinous animals have clogged intake pipes at power plants that pull in water from the ocean to cool machinery. That can cause the plants to temporarily shut down. Large masses of jellies also frustrate people who are fishing by damaging their nets and gumming up boat engines.

“There are definitely more reports of jellyfish blooms from more locations,” says Mark Q. Martindale, a marine biologist at the University of Florida. He explains that scientists are unsure whether blooms are really increasing or if reporting of the occurrences has just improved. However, Martindale says changing climate patterns and human activities, like overfishing, could be affecting jellyfish numbers. That could result in larger blooms showing up more often closer to shores—and in places where they haven’t been spotted before.

This is just one recent run-in between people and swarms of jellyfish in the worlds’ oceans. Reports of these events have been increasing for the past few decades (see Jellyfish Sightings). Swarms of jellyfish are called blooms. They can cover thousands of square miles and cause all sorts of trouble. Some power plants pull ocean water in through pipes to cool machinery. Jellyfish have clogged these pipes in places like Israel, Japan, the Philippines, Scotland, Sweden, and the U.S. That can cause the plants to shut down for a while. Large masses of jellies also make trouble for fishermen. The jellies damage fishing nets and gum up boat engines.

“There are definitely more reports of jellyfish blooms from more locations,” says Mark Q. Martindale. He’s a marine biologist at the University of Florida. He explains that scientists aren’t sure why. Are blooms really increasing, or are they just being reported better? But Martindale says changing climate patterns could be affecting jellyfish numbers. So could human activities, like overfishing. That could result in larger blooms showing up more often, closer to shores, and in completely new places.

FISHY CREATURES?

Although jellyfish have the word “fish” in their name, they aren’t actually fish at all. Jellyfish are invertebrates, meaning that their bodies have no bones. And unlike an actual fish, a jelly doesn’t have gills, a heart, blood, or a brain either. The bodies of these extremely simple animals consist of 95 percent water. Humans, for comparison, are 65 percent water. The rest of a jelly is made up of proteins and minerals that form cells, organs, and a flexible skeleton made of collagen. It’s the same material that allows the human ear and nose to bend.

Along with a bell-shaped body, a jellyfish usually has dangling tentacles that contain stinger cells called cnidae (NIGH-dee), which secrete venom. This toxic substance protects jellyfish from predators. Jellyfish, which are carnivores, also use their venom to stun prey, like small fish, shrimp, and other jellies. Even a dead jellyfish that washes up on the beach can still have functioning stingers.

Jellyfish may have the word “fish” in their name, but they aren’t really fish at all. Jellyfish are invertebrates. That means that their bodies have no bones. True fish have gills, a heart, blood, and a brain, but jellyfish don’t. Jellies are extremely simple animals. Their bodies are 95 percent water. To compare, humans are 65 percent water. The rest of a jelly is made up of proteins and minerals. These form cells, organs, and a skeleton that can bend. The skeleton is made of collagen. That’s the same material that allows the human ear and nose to bend.

Besides a bell-shaped body, a jellyfish usually has hanging tentacles. They contain stinger cells called cnidae (NIGH-dee). These cells secrete a toxic substance called venom. It protects jellyfish from predators. Jellyfish are carnivores. They also use their venom to stun prey, like small fish, shrimp, and other jellies. If a dead jellyfish washes up on the beach, its stingers may still work.

CHANGING WATERS

The goo-filled blobs people see floating in the water are only one part of the animals’ complex life cycle (see A Jellyfish’s Life). The creatures go through several different phases before reaching their adult form, called a medusa, with which people are most familiar.

Jellyfish start out as nearly microscopic larvae, the most immature stage of a jellyfish’s life. “This is the most vulnerable time for jellyfish because at this stage they’re food for a large number of small fish and other marine animals,” says Martindale. However, because of things like overfishing, there are fewer small fish to keep the number of jellyfish larvae in check.

Jellyfish look like goo-filled blobs floating in the water. But that’s only one part of their complex life cycle (see A Jellyfish’s Life). The creatures go through several different stages. Finally, they reach their adult form, called a medusa. That’s the form people see most often.

Jellyfish start out as larvae, the youngest stage of their life. They’re nearly microscopic. “This is the most vulnerable time for jellyfish because at this stage, they’re food for a large number of small fish and other marine animals,” says Martindale. But there are fewer small fish to eat jellyfish larvae. That’s because of things like overfishing.

Climate change is also disrupting ocean ecosystems. Martindale explains that warming seas have caused the growth of phytoplankton to peak earlier in the year. The tiny, plant-like organisms then die out sooner than they once did. Microscopic animals called zooplankton feed on phytoplankton. With less to eat, fewer zooplankton survive. That is a big problem for small fish that rely on zooplankton as a food source. Without as many fish around, jelly larvae have free rein to mature to adulthood and reproduce. And because one jellyfish can release 45,000 eggs a day, jellyfish numbers can quickly skyrocket.

Climate change is also upsetting ocean ecosystems. Martindale explains that seas are warming. That’s caused the growth of phytoplankton to peak earlier in the year. Then the tiny, plant-like organisms die out sooner than before. Microscopic animals called zooplankton feed on phytoplankton. Now zooplankton have less to eat, so fewer survive. Small fish need zooplankton for food, so that’s a big problem for them. With fewer fish around, jelly larvae are free to grow into adults and reproduce. And one jellyfish can release 45,000 eggs a day, so jellyfish numbers can quickly take off.

INVASIVE JELLIES

Climate change is also altering worldwide ocean currents, says Martindale. Water moving in a particular direction can shuttle invasive species of jellyfish thousands of miles. They can end up in places where they’re not normally found. “Jellyfish are prisoners of a current they find themselves in because they can’t effectively swim against it,” says Martindale.

Climate change is also changing worldwide ocean currents, says Martindale. These waters move in a certain direction. They can carry invasive species of jellyfish thousands of miles. The jellies can end up in places where they’re not normally found. “Jellyfish are prisoners of a current they find themselves in because they can’t effectively swim against it,” says Martindale.

Human behaviors also cause jellyfish to pop up in new locations. For example, jellyfish can hitch rides aboard ships. When a large ship docks, compartments in the bottom of the vessel fill with water to stabilize the ship. The seawater the boat takes on may contain jellyfish. The ship might dump the water—and jellies—at its next port, where the creatures could start a bloom in a new part of the world.

Scientists believe people might also be seeing more jellyfish blooms along coasts because of agricultural runoff. This water from farms contains fertilizers used to help crops grow. If these chemicals enter the ocean, they can cause algae to grow out of control. Algae blooms use up all the oxygen in water, creating dead zones that kill off fish and other predators that eat jellyfish. Plus, algae are a great food source for jellyfish polyps.

Human activities also cause jellyfish to pop up in new places. For example, jellyfish can catch rides on ships. When a large ship docks, spaces in the bottom of the ship fill with seawater. That keeps the ship steady. But that seawater may contain jellyfish. The ship might dump the water at its next port. It dumps out the jellies too. Then the creatures could start a bloom in a new part of the world.

Scientists believe agricultural runoff could also be leading to more jellyfish blooms along coasts. This water from farms contains fertilizers. The chemicals are used to help crops grow. But if they enter the ocean, they can cause algae to grow out of control. Algae blooms use up all the oxygen in water. That creates dead zones, where fish and other predators of jellyfish die off. Plus, algae are a great food source for jellyfish polyps.

Another reason we might be seeing more jellies near shores is the growing number of human-made structures. Martindale explains that jellyfish polyps naturally latch onto hard rock and coral. Artificial reefs, boat docks, and rock embankments give the organisms more places to grab on to and grow near beaches.

While getting stung by a jellyfish at the beach is no fun, Martindale explains that the animals’ stings are rarely life-threatening and the pain lasts only a short time. If you do get stung, he suggests washing your skin with vinegar, which neutralizes the toxin, then rinsing the area with warm water and applying ice. That’s good advice for the millions of beachgoers around the world who could run into jellyfish blooms this summer.

And we might be seeing more jellies near shores for another reason. The number of human-made structures is growing. Jellyfish polyps naturally grab on to hard rock and coral, explains Martindale. Many artificial reefs, boat docks, and rock embankments are placed near beaches. That gives the animals more places to grab on to and grow.

Getting stung by a jellyfish at the beach is no fun. But Martindale says that the animals’ stings are rarely dangerous. The pain lasts only a short time. What if you do get stung? He suggests washing your skin with vinegar. That counteracts the toxin. Then rinse the area with warm water and apply ice. That’s good advice for the millions of beachgoers around the world. Many of them could run into jellyfish blooms this summer.