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Stung! On Jellyfish Blooms and the Future of the Ocean 
by Lisa-Ann Gershwin.
Chicago, 424 pp., £19.50, May 2013, 978 0 226 02010 5
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Near the end​ of H.G. Wells’s The Time Machine, the Time Traveller finds himself on a desolate beach in the distant future. Under a lurid red sky, by a slack, oily sea, he is set upon by giant crabs, last survivors in a dying world – ‘foul, slow-stirring monsters’, with ‘vast, ungainly claws smeared with an algal slime’. If Wells were writing that scene today, the jellyfish would be a much better candidate than the crab for the part of the doomsday creature on the terminal beach. According to Lisa-Ann Gershwin’s disturbing book, the jellyfish is an ‘angel of death’, a harbinger of ‘planetary doom’ likely to be the ‘last man standing’ in what she describes as our ‘gelatinous future’.

Jellyfish are immensely old. From the fossil evidence, we know that they dominated the oceans for millions of years before predators with bones or shells or teeth evolved. ‘Through the eons,’ Gerswhin writes, ‘while trilobites and dinosaurs came and went and plants and animals moved onto land and evolved respiratory machinery and mammals evolved bigger and better brains, jellyfish stayed the same.’ With no brain, no heart, no lungs and no gills, they are ‘simple but effective’ – ‘essentially a gelatinous body with one or more mouths for ingesting food, one or more stomachs for digesting food, and usually four or eight gonads for making more jellyfish’. Species of the phylum Cnidaria – the classic jelly – have existed in something close to their current form for at least 565 million years; Ctenophora, the comb jellies, are not much younger. They survived the ‘big five’ mass extinctions. And now, it seems, they are experiencing a renaissance.

Stung! is a serious monograph, a guide to jellyfish biology and to the recent explosion in jellyfish blooms by an expert in the field. (Gershwin has devoted her working life to marine invertebrates and has discovered more than 150 new species; an American, she is now the director of the Australian Marine Stinger Advisory – ‘Consulting on all aspects of marine stinger management’.) But it’s a serious monograph disguised, quite convincingly, as a monster movie. It begins with a series of horrifying vignettes of jellyfish on the rampage, such as the ‘mass fish-kill’ events suffered by salmon farms. In 1998, a swarm of large Aurelia (the standard moon jelly)1 moved into Big Glory Bay off New Zealand’s South Island, and killed 56,000 three-kilo salmon in their pens within half an hour. Gershwin describes the incident in terrible detail:

The salmon all swim in one direction inside the circular pens, creating a fairly strong vortex that sucks water from the surrounding area. The Aurelia, being passive drifters, became entrained in the vortex. Too large to pass through the mesh, the jellyfish were pinned against the netting. As the jellyfish struggled against the current and the netting, their mucus, which is profuse and packed with stinging cells, was sucked into the cages. It appears that as the salmon inhaled the mucus, it blocked the oxygen-exchange surfaces of their gills, causing them to suffocate. The stinging cells exacerbated the problem by alarming the salmon, causing them to breathe faster, thereby serving to suffocate them faster.

At the time this seemed like a freak event. But since then, similar things have happened in salmon farms across the world: in Scotland, between 1999 and 2002, more than four million salmon died in their cages in ninety separate incidents. In addition, jellyfish have knocked out power stations in India, America, Israel and the Philippines by clogging the grills on their water intakes; disabled the nuclear-powered supercarrier USS Ronald Reagan, in the same fashion; and capsized a Japanese trawler, whose nets were filled with the ‘sumo-wrestler sized’ Nemopilema nomurai.2 They are more or less unstoppable, like water-borne zombies: ‘Chemical repellents don’t work, because jellyfish drift on the current and can’t respond. Electric shocks don’t work for the same reason. Acoustic shocks don’t work, because jellyfish, not having a brain, aren’t afraid of noise.’ Biocides don’t work because, alive or dead, jellyfish block pipes, fill nets and spread their stinging mucus.

Most of all, jellyfish have bloomed in vast numbers in bays, seas and oceans all round the world, driving swimmers off beaches and, far more important, dominating once rich ecosystems. One species, Mnemiopsis leidyi,3 a comb jellyfish native to the east coast of the US, invaded the Black Sea in vast numbers in the 1980s, having apparently been transported across the Atlantic in ships’ ballast tanks (it was standard practice until recently for ships to load up with ballast water in one port and dump these ‘floating zoos and botanical gardens’ in another, spreading invasive species and pathogens across the world). Summertime blooms in the Black Sea created densities of 300-500 specimens per cubic metre; 300-500 ‘fist-sized’ jellies in an area ‘no larger than the leg room under a small breakfast table’. Thereafter, Mnemiopsis spread through Europe’s seas ‘like cancer’ or ‘Hitler’s army’, invading the Caspian, where it helped bring about the extinction of the beluga caviar industry, then moving through the Sea of Marmara into the Aegean, the Ionian, even as far as the North Sea and the Baltic.

Partially enclosed bodies of water tend to be the worst affected: the 30 square kilometres of Lurefjorden in Norway are home to an estimated 35 million Periphylla periphylla, the red-coned ‘Santa’s hat’ jellyfish.4 But even the open ocean can be ‘flipped to a state of jellyfish control’. The Benguela Current off Namibia, historically a rich sardine fishery, is now dominated by two large species of jellyfish:

By mid-2010, the once-productive Benguela fishing region had become a ‘ghost town’, or ‘dead zone’. Dead and dying jellyfish sink to the bottom and rot. Millions of phytoplankton [single-celled aquatic plants] that were once eaten by copepods [tiny crustaceans] and other zooplankton, now uneaten, also die and sink to the bottom to rot. These masses of decaying carcasses create a zero-oxygen zone of hydrogen sulphide where nothing can survive. Vast expanses of the seafloor are now a moonscape, an eerie graveyard almost completely devoid of living things. Jellyfish dominate the surface waters above this dead zone. The jellyfish have excluded most other living things by partitioning their vertical and horizontal space into a stingy-slimy killing field impacting over 30,000 square nautical miles.

Seasonal jellyfish blooms have been recorded throughout history, but Gershwin argues that current events are on a completely different scale. In the whole of the last century, for instance, three large-scale Nomura blooms were recorded in Japanese waters. Then, starting in 2002, there were six in eight years. One recent study, of quantifiable jellyfish trends in 45 large marine ecosystems, found an increase in 28 of them; jellyfish populations were stable in 12 ecosystems, and decreasing only in two. All this is largely down to ‘anthropogenic perturbations’. The most obvious cause of multiplying jellyfish is overfishing. We have fished out or otherwise slaughtered its few predators – among them mackerel, tuna, sunfish, sea turtles and albatross. We have fished out its competitors, forage fish such as anchovies, pilchards, sardines and menhaden. In particularly grave cases, this allows the jellies to take ecosystems over entirely. They devour huge quantities of zooplankton, such as small crustaceans and the eggs and larvae of fish, which forage fish also rely on. So jellyfish kill fish directly by eating their young but also indirectly, by depriving them of food.

Most contemporary books about marine biology return, inevitably, to the theme of our terrible mistreatment of the sea. This one is no exception; and it gives a compressed, powerful and righteously relentless summary of all our various assaults on the ocean. Gershwin provides a brief overview of the work of fisheries biologists such as Boris Worm, Ransom Myers, Jeremy Jackson and Daniel Pauly, whose work underpins much media coverage of overfishing, such as the recent documentary The End of the Line. In a study from 2003, Myers and Worm found that, since the beginning of industrialised exploitation, 90 per cent of all large fish have disappeared. Typically, within 15 years of a new fishery opening, ‘community biomass’ will have been reduced by 80 per cent. Their work has been contested; if you prefer, a more conservative recent UN study suggests that a mere 72 per cent of all fish stocks are currently overexploited. But Gershwin argues that figures like these only make sense in terms of ‘shifting baselines’: each generation starts with lower and lower expectations of marine life.

Overfishing also has manifold indirect effects: the so-called ‘trophic cascades’ that disrupt whole ecosystems when a link in the food chain is removed. Take the case of the disappearing Aleutian sea otters in the Bering Sea. Forage fish in that area declined in the 1980s as a result of overfishing and climate fluctuation, which led to a decline in their pinniped (seal and sea lion) predators. As a result, killer whales were suddenly short of mammalian prey. So they turned on sea otters, which, being scrawny compared to juicy seals, were eaten in large numbers. As sea otters declined, so their main prey – sea urchins – increased eightfold in biomass, and voraciously grazed on kelp, ‘reducing once lush kelp forests to moonscapes of bare rock and crustose algae’. As the kelp forests disappeared, a whole ecosystem went with them – small fish, snails and ‘a myriad of gribblies living in the understory’. Pollock fisheries in the Bering Sea began to crash in the late 1980s; it is presumably no coincidence that at the same time jellyfish suddenly became wildly more abundant – so much more that the area north of the Alaskan Peninsula became known to fishermen as the ‘slime bank’.

But there are several baleful man-made influences besides overfishing at work, primarily the discharge of fertilisers and sewage, along with other forms of pollution, and climate change. Gershwin’s chief example is the most studied jellyfish bloom in history, in the Black Sea. It is one of the world’s most polluted bodies of water, the sole drainage sump for 165 million people in 22 countries, through its five large tributary rivers. Excess nitrates, phosphates and other pollutants have created a ‘critically eutrophic’ dead zone nearly twice the size of the one at the mouth of the Mississippi, which itself is about the size of Massachusetts. These nutrients encourage large but short-lived algal blooms which decay and create hypoxia (depletion of oxygen), causing fish and other animals to suffocate. Meanwhile, decades of overfishing have taken their toll. First the big fish – tuna, sturgeon, swordfish – were fished out. Initially stocks of forage fish, such as sprat and anchovies, rose as they were freed from their pinniped predators. Grateful fishermen took up the slack, and by 1990 they too had crashed. In addition, trawling had trashed the sea-floor habitat, killing off most of the mussels and other bottom-dwelling filter-feeders that had survived the hypoxia. Since filter-feeders usually cleanse vast amounts of water of its impurities, the water became dirtier and murkier still. By the late 1980s, the Black Sea was ‘the marine equivalent of a patient with HIV and emphysema’ – and Mnemiopsis was the marine equivalent of pneumonia.

Jellyfish​ are ‘marine weeds’, Gershwin says: hardy, fast-growing, fast-breeding, adaptable and tenacious. They have complicated but prolific reproductive strategies. They practise the ‘alternation of generations’. Typically, what we think of as the jellyfish, the medusa, reproduces sexually, spawning sperm and eggs which, once fertilised, turn into sea anemone-like polyps, which attach themselves to the jellyfish’s bottom or other surfaces. These, in turn, reproduce by cloning; when conditions are right, they ‘strobilate’, elongating and splitting into a stack of discs which develop into larvae, and break away to become medusae. They are tolerant of hypoxia, as well as changes in sea temperature and acidity levels that are fatal or disabling to many aquatic animals; they don’t mind murky waters, since they hunt by touch, with their tentacles, rather than sight; they don’t appear to be affected by many toxins, or even by radiation. They can eat vast amounts when times are good, and can even ‘degrow’ when food is scarce, consuming their own body mass very slowly, with no ill-effects. Jellies of 18 cm can degrow as far as 1.4 cm, then grow back up again, in a period of 120 days. In the case of Turritopsis dohrnii,5 the cells reaggregate when the medusa dies to form new polyp colonies, ‘the first known example of true biological immortality’, as if a dead butterfly’s cells had reformed into a caterpillar. In short, like rats or cockroaches on land, jellyfish are perfectly poised to capitalise when ‘ecosystems wobble’. They kill off all the competition, and because they have so few predators, they are largely a ‘trophic dead end’. Even when they die, they rot, helping to create hypoxia and encouraging toxic bacteria.

Stung! is not an unalloyed joy to read. Gershwin’s style could politely be called enthusiastic: ‘Some jellyfish species can get BI-I-I-I-G’; ‘The more jellyfish, the louder the siren and the redder the flashing lights that something is out of sync: “wwhoooop … wwhoooop … problem, problem!”’ She doesn’t always deal with the counter-arguments to her doomy, march-of-the-jellyfish thesis, weak and self-interested though they often are. I would have liked to see her address the criticisms of the Boris Worm school of fishery biologists more effectively, since they are often hard for the non-specialist to follow; the sections on global warming would not, I fear, satisfy a determined reader of the Sunday Telegraph. There is little on the various attempts to fight back the jellyfish tide, by breeding turtles, for instance, or fish that feed on them.

The outlook for the sea, Gershwin writes in what remains a fascinating book, is ‘essentially apocalyptic’. In the vast majority of fisheries we are still, as she puts it, fishing out the capital and ‘leaving the interest’ – or, in the case of bottom-trawling, burning down the bank to get our cash out. Stung! is a roll-call of crashed fisheries – Newfoundland cod, California sardine, Pacific hake, Pismo clam, white abalone, orange roughy – and extinct or severely endangered marine species: Steller’s sea cow, Mediterranean hammerhead, barndoor skate, vaquita, monk seal, Hooker’s sea lion, Kemp’s ridley sea turtle. A global tragedy of the commons is taking place in our time, which we ignore because it’s underwater. And even if we could persuade the world to do something about it, which we won’t, it’s probably, as Gershwin says, ‘too late’.

In the 1990s, there were about 125 known eutrophic dead zones around the world; by 2011 the official tally had risen above 530, with another 228 sites showing signs of stress. To quote Jeremy Jackson, these ‘will increase to form continuous swaths for thousands of kilometres within the century. Toxic blooms will also increase in size and frequency … with catastrophic effects on fisheries and agriculture.’ Meanwhile the acidification of the oceans, thanks to rising CO2 levels, is continuing apace; snails, corals and crustaceans are already losing shells and skeletons as the calcium carbonate leaches out. And every day we add more and more carbon dioxide and fertilisers and industrial waste.

So what’s left? After the big fish and the marine mammals have vanished, after the clams and worms have suffocated in the bottom hypoxia, and the snails and the corals and the calcified plankton have disintegrated, after the birds and the mussels and the sea cucumbers have choked on plastic … and the macroalgae have succumbed to the shading of the dinoflagellates, what is left?


Our gelatinous future awaits.

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Vol. 36 No. 8 · 17 April 2014

Theo Tait gives a compelling portrait of the jellyfish, and the threats posed by their increasing numbers (LRB, 6 March). However, his account of the jellyfish fossil record is inaccurate. The arrival of predators with hard parts occurred during the Cambrian, which was preceded by the Ediacaran. The Ediacaran fossil record is dominated by disc fossils, which were originally thought to be jellyfish owing to their shape, pliability and perceived evolutionary simplicity. This interpretation has since been shown to be incorrect for three reasons. First, the disc fossils have all been preserved showing the same side, which means that if they were jellyfish, they must all have been killed (or beached) perfectly face down, in contrast to modern beachings. Second, Ediacaran discs show no signs that they were capable of movement, and many possess rooting structures that indicate they grew in sediment.Third, possible tentacle-like structures in the fossils are symmetrical, in contrast to the interlocking tentacles observed when jellyfish are killed. As a result, Ediacaran discs are variously interpreted as rooting structures, microbial colonies or traces of the movement of other organisms – but never as jellyfish. While the Ediacaran may contain some cnidarian (the jellyfish phylum), there are no known medusae until the Cambrian, 60 million years after the age mentioned by Tait. Jellyfish do pose a problem for the future oceans, but their dominance of the oceans is not a return to the past.

Emily Mitchell

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