Slide Show: Jellyfish Jamboree--Are They Set to Seize the Seas?
A new paper proposes that humans are making the oceans a very happy habitat for jellyfish. Here's a closer look
Slide Show: Jellyfish Jamboree--Are They Set to Seize the Seas?
- HAPPY HABITAT Much about the jellyfish life history is still unknown. In the early larval stage, known as polyps, jellyfish are suspected to prefer hard surfaces onto which they can attach. Increasing costal development, offshore rigs and other objects may be aiding population booms by giving the baby jellies a solid habitat, notes the NSF.
One of the reasons so little is known about jellyfish development ("It's a little bit like talking about humans without knowing about children," says Costello) is that researchers can't seem to keep them alive in laboratories. WIKIMEDIA COMMONS/MALENE THYSSEN - FREE RIDE Jellies have hitched free rides all over the world, frequently traveling in the ballast water of ships. So when ocean water from faraway seas is dumped into, say, the Black Sea, where there is little native competition, invasive jellyfish can take over. That's exactly what happened in 1982, when comb jellies first arrived there by accident. By 1990, they had taken over the ecosystem and cost the fishing and tourism industries an estimated $350 million, according to the NSF. WIKIMEDIA COMMONS/STEVEN G. JOHNSON
- OVERFISHING Overfishing, as it turns out, is great news for jellyfish, which are now finding oceans an even better place to live and multiply, the study says. Popular fish species, including anchovies and sardines, feast on the same fare as the jellyfish, so when the fish numbers dive, a bigger buffet opens up for the jellies. Others posit that a decrease in species that feed on the jellyfish themselves has also allowed them to flourish. WIKIMEDIA COMMONS/DAVID GOEHRING
- CLIMATE CHANGE Although they don't technically have brains (they have a "nerve net" instead), jellyfish are no dummies. Many of them prefer—and thrive in—warmer waters, which could mean a big jump in jelly populations with global warming, the paper's authors propose. Although historical data on jellyfish populations is scarce, a previous study has noted that over 50 years, warmer years in the North Atlantic consistently brought more jellyfish.
Many of the more dangerous jellyfish also live in tropical waters. Warmer seas worldwide could also bring an expansion of their habitat with "severe repercussions for the tourist industry," write the study authors. WIKIMEDIA COMMONS/BUZZWOOF - DEAD ZONES After a large plankton bloom, the decaying organic matter sucks up much of the water's oxygen, turning the area into a eutrophic "dead zone." These dead zones—so called because few organisms can survive in these conditions—now make up about 100,000 square miles of the world's oceans, according to the National Science Foundation (NSF). The study authors explain that rather than perish with most of the other marine life, many species of jellyfish can thrive in low oxygen levels and feed on other remaining species, such as protists and flagellates. WIKIMEDIA COMMONS/MICHA L. RIESER
- SMART EATERS Jellyfish feed mostly on zooplankton, which thrive in nutrient-rich waters (often attributed to excess fertilizer and sewage runoff). As food becomes abundant, so, too, can the jellyfish. When conditions are ideal, hundreds of thousands can flourish, resulting in a full-on jellyfish bloom, or "swarm."
When faced with a food shortage, fish often become weak and perish, but starving jellyfish can simply shrink and return to healthy size once food becomes available again, explains the new report. This makes both individuals and whole populations impressively hardy, even during lean times. WIKIMEDIA COMMONS/STEFANI.DREW - GELATINOUS MENACE Jellyfish may elicit oohs and ahhs at aquariums, but out in the watery wild they can wreak rapid and serious bodily harm. The venomous sting of a box jellyfish known as the Chironex fleckeri can kill a person in three minutes.
They also pose a host of economic threats. An overload of jellyfish can burst fishing nets and contaminate catches. Costal waters thick with jellies can also clog cooling intakes at nearby power plants, notes a new study. Y. TANIGUCHI
