Jellyfish have no brain and consist of almost entirely water, but they have become a menace for coastal industries around the world. In recent years, they’ve wreaked havoc on fishing industries, tourism and have even clogged nuclear cooling systems.
Explosions in jellyfish populations are known as jellyfish blooms and while the data on these blooms aren't comprehensive, experts suggest that they are increasing in intensity, frequency and duration.
According to Quartz reporter Gwynn Guilford, “blooms have wiped out billions of dollars in earnings over the last few decades” in the fishing industry. The country of Japan, in particular, has been plagued by Nomura jellyfish, which can grow to be the size of refrigerators. In 2009, a net full of Nomura capsized a 10-ton trawler, Guilford said.
Jellyfish are also swarming popular tourist destinations in the Mediterranean and Australia, and some species can even be deadly, she said. The Irukandji jellyfish, which is “about the size of a double A battery”, according to Guilford, can cause brain hemorrhaging and heart failure.
Guilford said the population growth of jellyfish not only have wide-ranging ramifications but also potential causes.
“In areas where there is a high degree of human activity … jellyfish are increasing,” she said.
Some of the possible causes for the increase are overfishing, pollution and coastal development. Fishing industries have sharply decreased jellyfish predators like salmon, sea turtles and mackerel. Meanwhile, a decrease in oxygen in parts of the ocean due to pollution kill many types of fish, but “jellyfish don’t need that much oxygen so they thrive," said Guilford.
When it comes to fighting the population growth, Guilford said they are difficult to get rid of and some species actually reproduce themselves when cut.
According to Guilford, “Jellyfish aren’t really the problem. They’re the symptom of the problem.”