Last summer, while cruising Alaska’s fjords with the family, I kept an eye trained on the water in hopes of pointing out killer whales and dolphins to my children. We saw both, but, just as notably, passing by in the dark green, sunlit waters was an endless parade of large, white blobs. Jellyfish appeared to be the dominant life form in those waters. Indeed, in Alaska and elsewhere around the world jellyfish populations are increasing, often exploding in “blooms,” with dramatic effects on regional marine ecosystems and fisheries.
Some of the news stories call to mind science fiction accounts of alien invasions. At this National Pubic Radio site you can listen to “Jellyfish Take Over an Over-Fished Area,” a report by John Nielsen on one of the most severe, multi-year blooms, off the coast of Namibia. At this BBC site you can read about a jellyfish invasion in November 2007 that killed more than 100,000 fish at Northern Ireland’s only salmon farm, wiping it out. The stinging predators covered a ten-square-mile area to a depth of thirty-five feet. They were so dense in the water that fish farmers could not reach the pens holding the salmon to rescue them. National Geographic’s site Photo in the News: Blue Jellyfish Invade Australia Beaches provides a portrait of one of the more photogenic outbreaks, as well as links to other bloom-related articles. And Jellies in the News gives a list of links to current reports on blooms and other matters gelatinous; elsewhere on the site are beautiful photographs of the translucent animals.
The recent upswing in jellyfish numbers seems to far exceed natural fluctuations. Scientists generally blame the disruption of coastal ecosystems by people—be it nutrification of the water due to sewage and fertilizer runoff, overfishing of competitor fish species, depletion of sea turtles and other species that feed on jellyfish, or rising water temperatures from global warming. Like pigeons thriving in urban areas, some species of jellies may expand where the natural balance has been severely stressed. The National Resources Defense Council has an article on the problem entitled “The Blobs of Summer,” written by Lily Whiteman. Claudia Mills, an independent research scientist specializing in “gelatinous zooplankton” at the University of Washington follows jellyfish population trends closely. Her homepage has a great deal of information on jellies, including links to other sites and to scientific papers she has written on the subject. First, though, scroll down and click on “Marine Conservation,” where Mills provides further insight into the causes of jellyfish blooms. She notes that even jellyfish themselves are suffering from the disturbance of marine ecosystems; some species have declined due to habitat loss. She also underscores the difficulties scientists face in attempting to understand the effect of ecological disturbances: for most jellyfish species, little is known about the polyp stage of their life cycles.
Jellyfish are in the phylum Cnidaria, a diverse group of beautiful animals that includes corals and anemones. The University of California Museum of Paleontology has a good introduction to jellyfish and their close relatives. (Be sure to click on “Cubozoa” to learn more about the amazing box jellies, agile and often highly venomous predators, some of which have evolved eyes complete with lenses, corneas, and retinas.) True jellyfish are in a class of Cnidaria called Scyphozoa. That class is amply (and aptly) chronicled at The Scyphozoan, a site maintained by Mike Dawson, a post-doc at the University of California, Davis. I particularly enjoyed his material on the golden jellyfish that lives in marine lakes of Palau, in the south Pacific. To learn about the golden jellyfish’s curious daily migration and how it evolved, click on “Behaviors” on the site’s left-hand menu. Then go to How the jellyfish lost its spots to read the interesting tale of how the landlocked golden jelly evolved from oceangoing ancestors. For another article on the species, see “Darwin’s Jellyfishes,” an article in National Wildlife magazine by Pamela S. Turner.
Cnidarians have been around more than 500 million years, but new research indicates that they are not as primitive as most people imagine. The science writer Carl Zimmer reports on genetic studies that reveal considerable complexity in his article “Plain, Simple, Primitive? Not the Jellyfish,” which appeared in the New York Times on June 21, 2005.
No compendium of jellyfish links would be complete without a site exploring the animals’ incomparable ability to sting. Like their fellow cnidarians, jellyfish are equipped with nematocysts, specialized stinging cells that can fire a microscopic syringe to inject venom into a victim. One of the best sites to learn about these tiny, yet potent, weapons is that of the Tropical Australian Stinger Research Unit at James Cook University in Australia. Although the group’s research focuses on box jellies, true jellyfish possess similar stinging harpoons. The two species of greatest concern in Australia, due to the danger they pose for swimmers, are Chironex fleckeri (notorious as the world’s most venomous animal) and its diminutive but deadly relative Carukia barnesi, the Irukandji jellyfish. To view some amazing video clips of the nematocysts firing, go to the menu on the left of the group’s main page and select “General Biology.”
If you find the thought of massive blooms of stinging jellyfish disturbing, it might help to think about all the marine animals that prey on them. A Web site called TED (an acronym for Technology, Entertainment, Design) offers a lecture by marine biologist Tierney Thys, entitled “Swim with the Giant Sun Fish in the Open Ocean.” Thys has understandably fallen for this fish. It’s a top predator of jellyfish and one of the strangest animals you will ever see: it resembles an enormous, swimming fish head.
People, too, eat jellyfish. The Scyphozoan Web site has a page on how and where the animals are cooked and eaten. To meet the demand for dried jellyfish, considered a delicacy in China and other Asian counties, global harvests have risen to roughly 500,000 tons per year. It’s not a case of one exploding population controlling another, however: people only go for jellyfish that belong to the order Rhizostomeae, which tend to have larger, more rigid bodies than other jellyfish. When processed they have a desirable, slightly crunchy texture. Unfortunately, though we run the risk of depleting those species, the ones responsible for the oversize blooms never make it to our plates.