Jellyfish blooms are on the rise. Jellyfish, which are carnivorous creatures, are found in every ocean from the surface to the deep sea. The explosion in jellyfish populations could be an indicator of our oceans’ ailing health. (Photo: Reuters)

Jellyfish blooms are on the rise, with the past several decades seeing a dramatic increase and temporal shift in jellyfish distributions around the world. Sadly, this may be a sign that our oceans are in trouble.

"Jellyfish flourish when something's wrong," jellyfish expert Lisa-ann Gershwin told CBC Radio. "They're an indicator that something is out of balance."

Gershwin is director of the Australian Marine Stinger Advisory Services. In her new book called "Stung! On Jellyfish Blooms and the Future of the Ocean," she explores the "explosion" in jellyfish blooms, which refers to the large swarms of hundreds or even thousands of individual jellyfish, witnessed around fishing areas and coastal resorts.

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"The apparent increase in size and frequency of such blooms is convincingly linked to human activity, from global warming to overfishing, and habitat destruction to the introduction of fertilizers, toxic chemicals and trash," Gershwin wrote. Jellyfish blooms occur when ocean currents, nutrients, prey availability and water temperature bring the jellyfish together. Changes in these factors can cause jellyfish blooms to form more frequently, which Gershwin said we are now seeing.

One study on increasing jellyfish populations found that of the 45 marine ecosystems observed in the report, 62 percent of them showed increases in jellyfish blooms. CBC News reports that while jellyfish are quite low on the evolutionary totem pole (they even lack a brain), their increasing numbers are an indication that ocean environments are changing, and not for the better. Also, because the gelatinous jellyfish, a predatory plankton, feeds on things like plankton, crustaceans, small fish and fish eggs, it depletes the food resources of larger mammals like whales.

According to Gershwin's research, since the 1960s, nine out of ten of globally hunted fish are gone, including swordfish, marlin, sharks and tuna. Human activity has given rise to hundreds of coastal water "dead zones" where coral reefs, seagrass meadows and mangrove forests are in severe decline. "The increase in jellyfish blooms is one of many signs signaling a sea change," she wrote.

Jellyfish, a species of free-swimming marine animal over 500 million years old, survive best in nutrient-rich, oxygen-poor water. They also like warmer waters. Rising sea temperatures, a consequence of climate change, may be a reason for the explosion in jellyfish blooms.

According to JellyWatch, a research branch of the Monterey bay Aquarium Research Institute in California, the socio-economic impact of increasing jellyfish blooms include damages to tourism and fisheries. "Undoubtedly there are associated ecological ramifications such as food web and biogeochemical pathway alterations," the institute notes.

JellyWatch also reports that the rise in jellyfish blooms, while a sobering indication that our oceans are experiencing compositional changes for the worst, are, at this point, localized. More research into the problem of jellyfish blooms is needed before definitive efforts to curb the jellyfish explosion can be implemented.

Read more from iScience Times:

Can A Lab-Made Jelly Fish Help Fix Your Heart?

Stung By A Jellyfish? Hot Water, Not Pee, To Alleviate Pain

Jellyfish on the Rise: UBC Study