Jellyfish: Are They Taking Over In Sick Oceans?
Calling man-made warming “extremely likely,” the Intergovernmental Panel on Climate Change used the strongest words yet to describe how human activity is affecting the earth’s atmosphere and oceans.
Lisa-ann Gershwin sees evidence of global warming and human impact on the environment everyday in her work. She is one of a handful of jellyfish experts in the world.
Her research shows that a booming jellyfish population is displacing penguins in Antarctica, crashing world fisheries, possibly starving the whales to extinction, gumming up nuclear power plants, even bringing down national economies.
That’s because jellyfish thrive in the warmer, less-oxygenated water in many of the world’s oceans.
Gershwin joins us to discuss jellyfish. An excerpt of her book “Stung! On Jellyfish Blooms and the Future of the Ocean” is below.
- New York Review Of Books: They’re Taking Over!
Book Excerpt: ‘Stung!’
Chapter 2: Some Astonishing Ecological Impacts
All around the world, jellyfish are behaving badly—reproducing in astonishing numbers and congregating where they’ve supposedly never been seen before.
—Abigail Tucker, “Jellyfish: The Next King of the Sea”
If the expanding problem of jellyfish blooms only affected human convenience, it might not be that serious. We could find ways to deal with those sorts of problems. But in fact, major global ecological changes are occurring in our oceans today—and jellyfish blooms are one of the few things they have in common as an outcome. Indeed, jellyfish blooms are visual evidence of degrading ecosystems, and, in many cases, the drivers of further decline.
It should become evident from the following case histories that a truly astounding variety of species are causing an equally impressive variety of problems—and not just in one or two locations, but across the oceans and around the world, in just about every longitude and nearly every latitude, every depth, and every habitat. This is not a problem with an easy solution— this is a problem that is fundamentally changing our oceans globally.
Long considered the last wild frontier, Antarctica now appears to be “flipping” to a jellyfish-dominated ecosystem.
Jellyfish Replacing Penguins
On 3 November 2000, a news story was carried around the world about a research project investigating reports by British military personnel on the Falkland Islands that penguins would look up in unison to watch aircraft fly over, then topple over in regimental order. The whole colony. Like dominoes.
No doubt hilarious to some, toppling is not as funny as it sounds. Eggs break. Young get crushed or exposed to the bitter cold. Domino toppling would have serious repercussions on penguin reproduction and survival.
The reports of toppling penguins have been debunked as urban myth by a scientist with the British Antarctic Survey. It seems that they wobble but not topple. Hmmm. . . .
Domino wobbling isn’t the only modern, industrial-era threat that Antarctic penguins face. Like many other feathery, furry, and blubbery species, penguins feed on small crustaceans called krill. Vast swarms of krill used to dominate the surface waters of the Southern Ocean, where they were preyed upon by the abundant colonies of seals and albatrosses, pods of whales, and innumerable penguins. But now, the growing industrial demand for krill for aquaculture feed has exceeded supply in some areas. Krill are called “pink gold” in the industry. But as men mine their millions with ever-improving technology, life gets harder and harder for the penguins and other marine creatures who must now expend more energy traveling greater distances in search of food.
“Penguins in Antarctica to Be Replaced by Jellyfish due to Global Warming”— this was the newspaper headline from a story in the Telegraphon 19 February 2010. Imagine my curiosity. . . .
Krill are absolutely fundamental to the Antarctic food web. Whales, seals, seabirds, penguins—just about everything larger than a krill eats krill. And krill eat phytoplankton. Lots of it. Phytoplankton are, quite literally, tiny drifting plants (phyto, meaning “plant” + plankton, meaning “drifting”). Two main types of phytoplankton are fundamental to discussions about jellyfish: diatoms and dinofl agellates, which are discussed in detail in chapter 13. The other main type of plankton essential to discussions about jellyfish is zooplankton, or animal plankton. Copepods, a group of extremely abundant tiny crustaceans, are a key component of the zooplankton, but the term technically includes any animal organism that is at the mercy of currents, including larvae of most aquatic invertebrates and many types of fish, as well as jellyfish.
Huw Griffiths of the British Antarctic Survey has been researching the organisms that make up Antarctic food webs. He found that krill are being replaced by copepods, which are about 120 times smaller than krill—far too small for penguins but perfect for jellyfish, which filter small particles in the water with tentacles rather than hunt by sight.
One key to the problem is the shrinking sheets of sea-ice. Krill are concentrated in a narrow band along the edge of the sea-ice, where the young feed on algae living on the underside of the ice (Brierley et al. 2002). As the ice melts, so too does the primary grazing ground for the young krill and the length of the ice edge where the adults live. Furthermore, penguins use sea-ice sheets as breeding grounds, so any rise in temperature melts away the area available for raising young.
The other key to the problem is overfishing of krill. Never mind the politics, krill abundance has reduced at a rate of 40 percent per decade since 1976 (Atkinson et al. 2004). Already, penguins are showing signs of severe decline. According to Professor Ove Hoegh-Guldberg of the University of Queensland, the Adelie penguin population size has decreased by 70 percent since 1987 and emperor penguin numbers have declined by 50 percent since the 1970s (Hoegh-Guldberg 2005).
As penguins are replaced by jellyfish, other species that depend on krill will also face a similar fate. Consider Migaloo—the “White Fella”—Australia’s beloved albino humpback whale, and all the others on their krill-fueled migrations from feeding grounds to breeding grounds. What will sustain them?
While penguins and whales are emotive and charismatic, the real problem isn’t the loss of penguins and whales, per se, but the concomitant changes and losses of all the other components of the Antarctic ecosystem: the seals, the big fish, the seabirds, and the “other 99 percent” of species, that is, the invertebrates down the food chain. All are affected by these changes. Like a ratchet, click by click, each year the Antarctic ecosystem is constantly shifting toward a different community structure—one supporting jellyfish instead of penguins.
On the far side of the planet in the somewhat less chilly Arctic, a similar phenomenon is occurring. A type of seabird called a razorbill is the Northern Hemisphere equivalent of the penguin. In 2003, razorbills began stealing food from each other, a behavior that ecologists call “kleptoparasitism.” In fact, more than 60 percent of razorbills have been recorded stealing, while breeding success has declined to less than 40 percent (Lavers and Jones 2007). These changes have taken place as the birds’ food has shifted to less nutritious varieties, a shift thought to reflect the ecosystem and food chain effects of warming waters.
Similarly, it seems that climate change is causing polar bears to become cannibals (see plate 12). Prior to the 2000s, such events were rarely observed, but in the last eight years numerous incidents of polar bears stalking, killing, and eating other polar bears have been recorded (Amstrup et al. 2006; Mulvaney 2011). Researchers now believe that diminishing sea-ice and concomitant reduction in foraging opportunities may underlie this apparent behavioral shift.
Our frozen Arctic is thawing, and this has implications for all the organisms that depend on it. Consider high-latitude places like Hudson Bay, Baffi n Island off the coast of Newfoundland, and the icy Qaanaaq in northwestern Greenland. These locales are normally frozen by late November; however, the winters have been getting milder. Data from 1979–2009 indicates that the winter “freeze-up” in Canadian and Greenlandic narwhal summering localities has been progressively later by about 1 day each year (Laidre et al. 2012). At this rate, Santa’s elves may soon begin wearing shorts, T-shirts, and sandals to work, and snow globes may soon become as obsolete as the phonograph.
With animals that live on land but rely on the sea, such as penguins, razorbills, and polar bears, struggling to fi nd food, it seems that the more intimately associated with the sea an animal is, the harder its struggle to survive. In this next vignette, we examine what happens when key components of marine ecosystems experience what may initially seem like a minor blip. Except this time, instead of penguins, it’s sea otters. The mechanism is different, and the culprit jellyfish species is different, but the coupling phenomenon of jellyfish blooms with major ecosystem change is similar, as is the reverberation up and down the food chain.
Reprinted with permission from Stung! On Jellyfish Blooms and the Future of the Ocean by Lisa-ann Gershwin, published by the University of Chicago Press. © 2013 by Lisa-ann Gershwin. All rights reserved.
- Lisa-ann Gershwin, author of “Stung! On Jellyfish Blooms and the Future of the Ocean.”
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