The Jellyfish Chronicles

According to a new study, most jellyfish populations around the world are on the rise. Photo: Paul Caputo via stock.xchang

You’ve probably read the headline hundreds of times: Human Activity Threatens Survival of Species X. Given nature’s seemingly boundless creativity, you might well start to wonder if there isn’t, somewhere on the planet, a group of creatures for which all this anthropogenic activity might actually be a blessing, rather than a curse. A new study from the University of British Columbia may just provide the answer, in the form of the humble jellyfish.

Before I make my case, I want to deal with any sticklers out there who may complain about the use of the term jellyfish. I am fully aware that the gelatinous things are not in fact fish, and that the term jellyfish lacks a rigorous scientific definition. To be clear, this study is about the free-swimming members of three groups: cnidaria (jellyfish), ctenophora (comb jellies), and the salps. In other words, anything that would make you say “oh, a jellyfish,” if you saw it swimming by. If you want to be pedantic and call them sea jellies, be my guest, but I won’t.

The study in question was recently published in Hydrobiologia by Lucas Brotz, a PhD candidate at UBC’s Department of Earth and Ocean Sciences. “Historically, jellyfish have slipped through the cracks,” says Brotz. “They were perceived as an unimportant nuisance to fisheries scientists, yet they are too big to be studied by planktologists. But we now know that they’re very important in the marine ecosystem.” In the last decade or so, there’s been a lot of talk within the fishing community about unusually high jellyfish populations, but nobody had actually tried to pin down the data worldwide. Brotz and his co-authors decided to be the first.

The group divided the ocean into 66 areas called large marine ecosystems (LMEs). Examples would include the Gulf of Mexico LME, or the California Current LME. Within each of these areas, they gathered various records of particular species in a particular location over a particular period of time. I’m delighted to report that the official name of such a record is a “jellyfish chronicle.”

To account for the patchiness of the data, Brotz and his collaborators employed an analytical technique called fuzzy logic. The jellyfish chronicles were each given a score for the space and time they covered, as well as the reliability of the data. Thus, an anecdotal account of increased abundance over a particular summer would be given a relatively low score, whereas a large-scale, rigorous scientific monitoring program spread over 15 years would be given a high score. Chronicles with higher scores carried more weight in the final analysis, but even low-scoring chronicles could nudge the needle in one direction or another if there were enough of them. In this way, the team was able to extract an overall trend for each LME.

Jellyfish map, Brotz et al., 2012

Population trends of native and invasive species of jellyfish by LME. Red: increase (high certainty), orange: increase (low certainty), green: stable/variable, blue: decrease, gray: no data. Circles represent jellyfish populations with relative sizes reflecting confidence in the data. From Brotz et al, 2012. Used with permission.

The results? Of the 66 LMEs in the world, 45 had enough data to note a trend. Of these, 62 per cent showed an increase in jellyfish populations since 1950. By contrast, only 7 per cent showed a decrease. The rest had populations that were either stable or so volatile that no trend could be noted.

Nemopilema nomurai

Giant jellyfish (Nemopilema nomurai) interfere with fishing in Japan. Photo: Niu Fisheries Cooperative

Human activity can affect jellyfish populations in many ways. Overfishing can remove predators and/or species that compete with jellyfish for food. Structures like piers, wharves, oil rigs and shipwrecks provide ideal habitat for juvenile jellyfish, many of which live anchored to surfaces like their cousins the corals and sea anemones. Eutrophication, which produces areas of low oxygen called dead zones, affects other species more than jellyfish, which are able to survive reasonably well on little oxygen. But Brotz cautions that there is no smoking gun, at least not yet. “It’s not happening everywhere: there are certainly areas that have a lot of coastal development without an increase in jellyfish, and there are also areas that aren’t impacted by humans as much and still show increased jellyfish populations,” he says. “But if we take a big-picture point of view, it does look like there is a correlation between human development and jellyfish.” Of course, jellyfish can be a pain to humans as well, and not just from stings. Jellyfish blooms can clog water intake pipes and wreck fishing gear, and in some cases even capsize boats by their sheer weight in the net.

Because they have no hard body parts, jellyfish fossils are hard to come by, but those we have stretch back almost 600 million years, in short to the very origins of multicellular life. Through volcanic eruptions, cosmic impacts, and at least five severe mass extinctions, the simple, elegant design of the jellyfish has enabled it to endure the worst times this planet has ever seen. It’s not unreasonable to suppose that jellyfish do particularly well when other species are struggling, which is why I find Brotz’s final words both intriguing and worrying.

Something like 99.9 per cent of all species have gone extinct throughout time, so it’s interesting that so many species of jellyfish have survived. Part of that is their ability to adapt to changing conditions. The fact that they may be so successful right now highlights the number of rapid changes taking place. Given that, it’s pretty amazing to me that even in developed areas, we know so little about the jellyfish population. It’s time to start paying attention to them. I think they’re trying to tell us something.

1 comment

  1. Mojgan

    Great post! I like the idea of a jellyfish apocalypse as opposed to a zombie one. I hope they’ll like cookies, cause that’s all I’ll have to defend myself with [gulp].

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