Preface.  As we overfish, eutrophy and acidify the ocean with fertilizer and pesticides we risk a tipping point where jellyfish dominate the oceans and fish are scarce.

Related: Why and how Jellyfish are taking over the world

Alice Friedemann  www.energyskeptic.com  Author of Life After Fossil Fuels: A Reality Check on Alternative Energy; When Trucks Stop Running: Energy and the Future of Transportation”, Barriers to Making Algal Biofuels, & “Crunch! Whole Grain Artisan Chips and Crackers”.  Women in ecology  Podcasts: WGBH, Planet: Critical, Crazy Town, Collapse Chronicles, Derrick Jensen, Practical Prepping, Kunstler 253 &278, Peak Prosperity,  Index of best energyskeptic posts

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Javidpour J (2020) Cannibalism makes invasive comb jelly, Mnemiopsis leidyi, resilient to unfavourable conditions. Communications Biology.

An invasive comb jellyfish is able to survive by eating its babies to survive long and nutrient deprived winters.  This study also addresses wider questions of cannibalism in the animal kingdom. Cannibalism has been recorded among over 1,500 species, including humans, chimpanzees, squirrels, fish, and dragonfly larvae.  And it is especially common in aquatic systems for unknown reasons.

CNN (2020) Beach ball-sized jellyfish capable of damaging boats spotted in South Carolina

Wildlife officials in South Carolina are asking boaters to keep their eyes peeled for an invasive species of jellyfish that can grow to beach ball size and are big enough to damage boats and fishing equipment. They can get stuck in boats’ water intake lines, gobble up fish and shellfish eggs, and put a strain on fishing nets when they get scooped up and difficult to remove from the net.

Vince G (2012) In the last decade enormous plagues of jellyfish have been taking over the seas. And it is our fault. BBC.

Reactors at a Scottish nuclear power station have been shut down after enormous numbers of jellyfish were found in the sea water entering the plant. Huge annual jellyfish blooms have been cropping up across the Mediterranean, the Black Sea, the Gulf of Mexico, and the Yellow and Japan Seas. 

Is this a bizarre blip in the continually changing balance of oceanic life, or the beginnings of a new state change in marine diversity? Or in other words: in the Anthropocene, will the seas be filled with slime?

If they are, we face some serious problems. Last year alone, nuclear power plants in Scotland, Japan, Israel and Florida, and also a desalination plant in Israel, were forced to shutdown because jellyfish were clogging the water inlets. The entire Irish salmon industry was wiped out in 2007 after a plague of billions of mauve stingers – covering an area of 10 sq miles (26 sq km) and 35ft (11m) deep – attacked the fish cages. Two years later, a fish farm in Tunisia lost a year’s production of sea bream and sea bass after jellyfish invasions.

Perhaps the most extraordinary blooms have been those occurring in waters off Japan. There, refrigerator-sized gelatinous monsters called Nomuras, weighing 485lb (220 kg) and measuring 6.5ft (2m) in diameter, have swarmed the Japan Sea annually since 2002, clogging fishing nets, overturning trawlers and devastating coastal livelihoods. These assaults have cost the Japanese fisheries industry billions of yen in losses.

Human factor. Marine ecologists are warning of worse to come, and pointing the tentacle of blame at us. Some researchers fear that human changes to the marine environment may be leading to a tipping point in which jellyfish will rule the oceans, much as they did hundreds of millions of years ago in pre-Cambrian times. In 2009, Australian marine scientist Anthony Richardson and his colleagues published a research paper entitled The jellyfish joyride, in which they warn that if we do not act to curb current blooms, we will experience runaway populations that will cause open oceanic ecosystems to flip from ones dominated by fish biodiversity to ones dominated by jellyfish.

The problem is that no one really knows what causes the blooms. Some believe that population explosions result from overfishing of their dining competitors and predators, which include more than 100 species of fish, and animals such as turtles. However, other researchers point out that overfishing also hits jellyfish by reducing their food availability.

Either way, what is clear is that jellyfish are simply better prepared than other marine life for many of the ways humans are changing the ocean environment, such as warmer temperatures, salinity changes, ocean acidification and pollution. In this sense, humans might be jellyfishes’ best friend.

For instance, pollution can cause algal blooms that reduce the water’s oxygen content. This hits muscular swimmers like fish hard, but jellyfish can cope far better with these conditions.

Warmer water encourages jellyfish reproduction, and they can also better tolerate population crashes because their reproductive strategies are complex and adaptable. Some species of jelly can clone themselves, whereas others reproduce sexually but also have a polyp stage – like corals, with which they are related – that allows large populations of immature individuals to multiply while waiting for the right conditions to mature into adulthood. In these ways, they can withstand impacts that devastate other marine species.

Even the coastal infrastructure we build seems to be working to their advantage. Rob Condon, a marine scientist at Dauphin Island Sea Lab in Alabama, says that the pontoons, piers and even drilling platforms help provide anchors for jellyfish polyps, encouraging local population explosions.

Slippery customers

But Condon, who set up a global jellyfish database initiative (the wonderfully named JEDI) to monitor blooms, says that the “jellygeddon” scenario envisioned by Richardson and others is unlikely. Jellyfish blooms are nothing new, says Condon, “4,000 years ago in Ancient Crete, they used to paint jelly blooms on their pottery, and even in the 1920s, media were reporting “unprecedented” numbers of moon jellyfish in Monterey Bay.”

Gathering data on jellyfish is notoriously difficult. Although 70% of the planet is covered by ocean, we really only have a hazy idea about most of the life outside of coastal or estuarine zones. Jellyfish, which inhabit open oceans and deep waters, are still an enigma in many ways. Monitoring individuals and blooms cannot be done by satellite because they are so transparent, have very low biomass, and often occupy waters below the optical depth for satellite penetration. Even finding polyps and larvae in sea grass is tricky. 

Extreme measures

Dealing with blooms where they do turn up is tricky.  Even if you trap a bloom, what do you do with all those jellyfish? Japanese fishermen initially tried chopping them up in the waters, only to discover that the Nomura’s jellyfish defense strategy is to release its sperm and eggs, thus propagating the problem. In Spain, special jelly patrols were buried them in landfill.

But we don’t know what environmental effects destroying blooms could have. Jellyfish are an important food source for apex predators, and if we start tinkering with the natural bloom system, we don’t know what the ripple-down effects may be. They may even help mix and fertilize the world’s oceans, some researchers think.

Perhaps one solution is to sustainably exploit their abundance. Jellyfish do have their uses: in collagen preparations (to treat rheumatoid arthritis, for example), they are popular attractions in aquaria, and their fluorescent proteins have been instrumental in biomedical discoveries.

And, of course, they are a source of food. In Japan and other parts of Asia, jellyfish are dried and chopped into noodle-like strips to be added to soups, for example. Some entrepreneurial Japanese are even making vanilla-and-jellyfish ice cream. Jellyfish are 80% protein and very low in fat, although the high sodium content probably outweighs their health benefits.

So… jellyfish and chips anyone?

Richardson AJ et al (2009) The jellyfish joyride: causes, consequences and management responses to a more gelatinous future. Trends in Ecology and Evolution.

Human-induced stresses of overfishing, eutrophication, climate change, translocation and habitat modification appear to be promoting jellyfish (pelagic cnidarian and ctenophore) blooms to the detriment of other marine organisms. Mounting evidence suggests that the structure of pelagic ecosystems can change rapidly from one that is dominated by fish (that keep jellyfish in check through competition or predation) to a less desirable gelatinous state, with lasting ecological, economic and social consequences.

Jellyfish outbreaks can have many deleterious consequences, including losses in tourist revenue through beach closures and even the death of bathers; power outages following the blockage of cooling intakes at coastal power plants; blocking of alluvial sediment suction in diamond mining operations; burst fishing nets and contaminated catches; killing of farmed fish; reduction in commercial fish abundance through competition and predation; and as probable intermediate vectors of various fish parasites.