Jelly blooms - Will you be eating jellyfish burgers in the future?

No brain, delicate enough to be killed by a bubble, bad swimmers, and... taking over the ocean? Jellyfish, on the surface, may seem like an unlikely set of creatures to be concerned about. Yet in recent years, jellyfish have become a huge problem in certain parts of the world, clogging fishing nets, shutting down power plants, and stinging vacations swimmers. While there isn't solid proof that the number of jellyfish is increasing globally, there has been a dramatic increase in specific regions, leading to concern that the future of the oceans may be gelatinous.

Cnidarians - Wikimedia Commons

Jellyfish fall into two separate groups: cnidarians and ctenophores. Both groups have bodies that are gelatinous, are generally poor swimmers, and filter feed. The largest difference between the two groups is that cnidarians have long tentacles with stinging cells. These are the ones you want to avoid when swimming. Ctenophores, also known as comb jellies, are harmless and can't sting. 

Ctenophors, or comb jellies - Wikimedia Commons

But why are animals that can't swim and that have such delicate bodies doing so well when so many species seem to be struggling? It's because jellyfish are what we call generalists, organisms that can live in a variety of places and eat a variety of food sources. Jellyfish do well when other species have trouble. Many species need just the right combination of temperature, oxygen, light, and even salt in the water, but jellyfish are resilient to these changes. We are also giving jellyfish a leg up. Humans frequently fish for species that eat baby jellyfish, meaning more baby jellies survive. Finally, with seawater getting warmer, jellyfish reproduce faster. In general, when humans throw a coastal ecosystem out of whack, jellyfish are the ones to remain, and not just remain but thrive. 

These jellyfish can be a menace of the seas for a number of reasons:

1. They cause emergency shut downs in power plants, even nuclear ones. A lot of these power plants take in seawater to cool off the machinery. When the water is too full of jellyfish, it clogs up the entire plant, putting it in danger of overheating and making it necessary to close the plant until the jellyfish can be removed.. This can cause power outages in the region and ultimately costs a lot of money.
2. Jellyfish wreak havoc on fishers. They clog up the nets, sometimes so densely that the nets will break, and even sank a 10-ton fishing trawler in Japan. Jellyfish also eat baby fish, meaning that once there is a huge bloom of jellies, fewer fish make it to adulthood. Even if the nets of the fishers weren't entirely clogged with jellyfish, at this point there would be fewer fish to catch.
3. Jellyfish can get in the way of tourism. Nobody wants to go swimming in waters where they are likely to get stung.
4. A large presence of jellyfish can actually suffocate other animals. Jellyfish need less oxygen in the water than most species of fish. However, when jellyfish die, especially en masse, their bodies are decomposed by bacteria, which use up the oxygen that is in the water. This leaves little for fish to breathe, making water inhospitable for animals besides jellyfish and bacteria.

Massive blooms of giant jellyfish used to be rare. According to Shin-Ichi Uye, in Japan, where blooms of giant jellyfish have brought global attention, there used to be a massive bloom of jellyfish every 40 years. In the early 2000s, however, a massive bloom happened in 2002, 2003, 2005, 2006, and 2007. This particular species of jellyfish, Nemopilema nomurai, is massive: they can grow to be 6 feet wide and weigh over 440 pounds each! The fishing industry struggled as a result. In 2005 alone, fishers filed 100,000 complaints about the jellyfish. What did they think the cause was? Japan blamed it on water running into the ocean from China, bringing nutrients used for farming into the water. This could cause algae blooms and low oxygen conditions that jellyfish thrive in while other species suffer. Luckily for Japan, there haven't been huge blooms of jellyfish in recent years, but the experience was enough to leave people nervous.

Nemopilema nomura, the giant jellyfish sinking boats in JapanWikimedia Commons

Japan isn't the only place to see an uptick in jellyfish blooms. There have been problems in the Black Sea, in the Mediterranean Sea, and in many east Asian waters. Most of the places that have the most trouble with jellyfish blooms are the ones where there is the most human impact, meaning humans fish more there, there is more nutrients in the water from farming, there is more construction, and there are more non-native species that are brought to these waters, often the offending jellyfish themselves. But are jellyfish increasing globally? If waters get warmer, have less oxygen, and become more acidic, all things that we see happening, doesn't that set the stage for an ocean dominated by jellyfish?

Jellyfish and roast duck salad
Wikimedia Commons: Credit Line

Maybe. The problem is that jellyfish populations tend to fluctuate over the span of many decades. If the number of jellyfish fluctuate in a pattern every 40 or 50 years, you need a record of jellyfish that is at least 40 or 50 years long to say anything definitively, and in most cases we just don't have that. But with all the changes we see happening to the ocean, it is entirely possible that we will see more frequent, larger blooms in many areas.

So what can we do besides reduce pollution and do what we can to slow climate change? The answer may sound familiar; it is often a proposed solution when an animal takes over an ecosystem. We could eat them. In fact, in order to tackle a troublesome surplus of jellyfish in the Mediterranean Sea, there has been an effort to get Europeans to eat jellyfish. Chinese and Japanese cultures already embrace eating jellyfish. If life gives you lemons, make lemonade; if the ocean gives you jellyfish, make jellyfish burgers.