A Jellyfish Population Explosion? Globally, Yes... But Not Locally

I bought my daughter a few high-caliber squirt guns for her 12th birthday, and she and her friends had a blazing, rollicking gunfight in the warm waters of the Chesapeake Bay on Saturday.

The laughter quickly ended, however, when my daughter was stung on the belly by a sea nettle. These spectral agents of anguish, of course, have been a bane to Bay swimmers for millennia. But I was pained to read this morning that they and their ghastly jellyfish cousins may be on the rise worldwide because of reduced oxygen levels in the world’s oceans. (Interestingly, the jelly boom may be global -- but not local. But more on that later.)

Author Carl Zimmer writes in the blog e360 that some scientists are predicting a “global oxygen crisis,” in the world’s bays and oceans, not only because of increased water pollution (especially nitrogen and phosphorus fertilizer runoff, a well-documented problem here in the Chesapeake), but also because of global warming.

Zimmer explains that as water gets warmer, it can hold less dissolved oxygen.  Moreover, climate change is expected to reduce the mixing of the oxygen-rich surface waters with the oxygen-poor deeper waters.

“While fishes and other animals with high oxygen demands suffer, jellyfish may thrive,” Zimmer writes. “Jellyfish can tolerate lower oxygen levels than fish, in part because they can store reserves of the gas in their jelly. Free from competition and predators, jellyfish will be able to feast on the microscopic animals and protozoans that feed on algae.”

In other words, gasping and dying fish…. But numerous fat and happy jellyfish.

Science Daily, among other publications, has reported on the global jellyfish population boom -- including some six-foot-long monsters weighing more than 400 pounds.

That's the worldwide picture.  However, more locally, with sea nettles in particular, the numbers in recent years appear to be relatively low compared to past decades.

Margaret Sexton, a researcher at the University of Maryland Center for Environmental Science, said today that she has not seen an abnormally high number of sea nettles this summer near her lab's docks in Horn Point, on the Choptank River.

But she added: "It is not unusual for the peak to happen in late August or September. Also, my visual counts are a very localized measure. I've been hearing reports of higher abundances farther up the bay, especially near the mouth of the South River."

On August 26, Raleigh Hood of the University of Maryland Center for Environmental Science, reported: "Abundances in our area have been relatively low so far this year."

On the other side of the Bay, numbers of sea nettles counted by researchers are relatively small compared to past decades, according to Denise Breitburg, senior scientist at the Smithsonian Environmental Research Center. "Nothing unusual about this year from our counts in Solomons," Breitburg wrote in an email. "In general, numbers at Solomons (the only site with a good long-term record in Chesapeake Bay) are down considerably relative to the 60s and 70s."

The Maryland Sea Grant News & Notes website last year published an article based on Breitburg's research, that said sea nettle populations in the Bay may be declining as oyster populations in the Bay fall. More recently, Jack Greer beat me to the punch by writing an interesting article about Breitburg's findings in the Chesapeake Quarterly's Bay Blog.

"Since the late 1980s the density of sea nettles has seen significant declines," the 2009 Maryland Sea Grant report states. "One reason for this may be the loss of oysters. While sea nettles protect oysters from predation, oysters, in turn, have a role in nettle survival. Sea nettle polyps use oyster shell as substrate from which to grow."

Beyond just the nettlesome issue of jellies in the Bay, however, there may be much bigger problems looming on the horizon for the world's oceans. “Unless we find a way to rein in our carbon emissions very soon, a low-oxygen ocean may become an inescapable feature of our planet," Carl Zimmer writes in e360.

And that will sting all of us.

Comments

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On the other side of the Bay, numbers of sea nettles counted by researchers are relatively small compared to past decades, according to Denise Breitburg, senior scientist at the Smithsonian Environmental Research Center.

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Sea nettle polyps use oyster shell as substrate from which to grow.