Jellyfish Swarms are Bad News for Ocean Ecosystems
Book Review: Stung! On Jellyfish Blooms and the Future of the Ocean
In 2006, actors Kate Hudson and Matthew McConaughey flew to the Great Barrier Reef in Australia to film the Hollywood hit, Fool’s Gold. The movie was about scuba diving for sunken treasure, pleasure cruising, and rekindling romance. But when McConaughey’s stunt double got stung by the venomous Irukandji jellyfish and had to be airlifted to hospital, filming came to a grinding halt. Warner Brothers moved the set further south to the Whitsunday Islands, but when filming recommenced, another Irukandji stung a safety officer. Once again, filming was terminated and the shoot relocated.
photo by Loozrboy, on Flickr
This is just one among many stories of “jellyfish behaving badly” that marine biologist and ecologist Lisa-ann Gershwin describes in Stung! On Jellyfish Blooms and the Future of the Ocean. She also recounts how jellyfish once crippled the USS Ronald Reagan, one of the world’s largest aircraft carriers, when the engine sucked in thousands of these gelatinous creatures. Jellyfish have disabled nuclear power stations, clogged desalination plants, and decimated salmon farms. These creatures are, however, much more than a nuisance to humans; they are often the harbingers of an ailing ocean. “As seas become stressed,” Gershwin writes, “the jellyfish are there, like an eagle to an injured lamb or golden staph to a postoperative patient – more than just as symptom of weakness, more like the angel of death.”
Jellyfish swarms are not a new phenomenon. In central Wisconsin, jellyfish fossils in sandstone quarries tell us that these aquatic invertebrates have been around for at least 565 million years, and that jellyfish blooms have been frequent occurrences. However, Gershwin makes a strong and convincing argument that most present-day jellyfish swarms are caused by human activities such as overfishing, pollution, and marine habitat destruction. And when jellyfish take over an ecosystem, it is unlikely that it will ever recover to its original state.
Gershwin uses the Black Sea as a prime example of jellyfish invasion and ecosystem collapse. While much of the Black Sea is naturally anoxic and contains high amounts of hydrogen sulfide, anthropogenic changes have put incredible stress on the upper 13 percent of the sea, the shallow surface and shelf waters that can support life. For decades, the Black Sea has acted as a drainage sump for 22 industrialized countries, accumulating pesticides, fertilizers, heavy metals, and radioactive waste. These excess nutrients triggered massive phytoplankton blooms, depleting the sea’s remaining oxygen. Additionally, most piscivorous species have been fished out, including the mackerel — a natural predator of jellyfish. This allowed Mnemiopsis leidyi, a comb jellyfish indigenous to the eastern coastlines of the Americas, to enter the Black Sea in the early 1980s.
The Mnemiopsis, which Gershwin labels as a “marine weed,” travelled to the Black Sea in the ballast water of foreign ships. Despite its many problems, the Black Sea was still a prolific anchovy fishery then. However, the Mnemiopsis preyed on anchovy fish eggs and larvae and consumed the same zooplankton that the anchovies ate. Soon the anchovy fishery crashed and the Mnemiopsis bloomed in sensational proportions. “By 1993,” Gershwin writes, “it was estimated that Mnemiopsis comprised up to 95 percent of the total wet weight biomass” of the Black Sea.
Miraculously, the Black Sea recovered (although not to its former glory), but jellyfish continue to wreak havoc in oceans around the world. As Gershwin explains, jellyfish thrive on ecosystems in distress. They can survive in hypoxic (low oxygen) zones, acidic water, and rising sea temperatures. Most types of pollution do not affect them. Jellyfish are also extraordinary breeders and eaters. They can clone, self-fertilize, and produce tens of thousands of eggs every single day. They feed continuously, sometimes eating up to ten times their own body weight. And when food is scarce, jellyfish can “degrow,” and still remain perfectly healthy and fertile.
If these facts aren’t frightening enough, Gershwin discusses how jellyfish actually promote climate change by releasing carbon-rich mucus and fecal matter. Marine bacteria uses this jellyfish “goo and poo” for respiration, which creates even more carbon dioxide. “Climate change promotes jellyfish blooms and jellyfish blooms promote climate change,” Gershwin explains, “and like all robust feedback loops, where it stops nobody knows.”
Stung! can be an incredibly depressing read, especially since Gershwin suggests that it’s “too late” to fix the ocean’s problems, and that we can’t do much to stop jellyfish from taking over the oceans. However, her conversational tone and humorous language somehow makes the bad news easier to digest. And in my opinion, it is much better to know these hard-hitting facts than to be kept in the dark. Even if we can’t stop the jellyfish, we can, and must, do what Gershwin suggests on the last page of her book: “Adapt.”