Volume 12, Issue 27 ~ July 1-7, 2004
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Earth Journal
by Gary Pendleton

Sea Nettles
It’s summer in Maryland, that means oppressive heat and humidity. What can you do to find relief? Sit in the shade with lemonade, and you’ll be swatting tiger mosquitoes. If you take a walk in the woods, watch out for deer flies and poison ivy. To cool off, you could take a swim in Chesapeake Bay — if you don’t mind being stung by sea nettles. You might as well take in a movie.

The species of gelatinous zooplankton or jellyfish known as sea nettle is more abundant in the brackish waters of the mid-Chesapeake Bay and its tributaries than anywhere else in the world. That’s because sea nettles thrive in waters with middling salinity levels between 10 and 20 parts per thousand. Lucky us!

In case you didn’t know, a sea nettle looks like a milky blob of Jello with long stringy tentacles afloat in the water. The tentacles contain millions of stinging cells. The stinging cells have two purposes: They protect the sea nettle from predators and they attack and kill prey.

Jellyfish are major predators of fish larvae. Does that mean that jellyfish could be harmful to rockfish, bluefish and other important Bay species? Not necessarily, according to Merrill Leffler, writing in Maryland Marine Notes Online. Comb jellies and other gelatinous species also consume fish eggs. When nettles and comb jellies occur at the same time, predation decreases.

It might be that sea nettles also consume comb jellies. If the nettles are filling up on comb jellies, they might not be hungry for eggs and larvae. Is it possible that a major predator is actually protecting the species it preys upon? Could be.

Natural ecosystems like Chesapeake Bay are complex, and the relationships among Bay creatures are equally complicated. Ecologists know that predator species often play critical roles in helping maintain healthy populations of their prey species.

So anyone who would lobby for eliminating jellyfish would be unlikely to get much sympathy from the scientific community. Besides, people have tried in vain to thwart sea nettles using methods ranging from exclusion nets to toxic chemicals. The former method is not very effective, and the latter is dangerous to the environment.

The only thing known to reduce sea nettle levels is rain. Large infusions of fresh water caused by heavy spring and summer rains reduce salinity levels and keep the sea nettles away. But low salinity also hurts the blue crabs, and that isn’t good.

Instead of praying for rain, we might hope for clean and somewhat salty water with healthy populations of all the creatures that call the Bay home.

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