Fishing for an Explanation

We just finished reading the May 6 Washington Post article entitled, "Jellyfish 'Blooms' Could Be Sign of Ailing Seas," and, boy, we're confused. Jellyfish, affectionately known as "rats of the sea," seem to be undergoing a population explosion.

Why? Well, there are several possible explanations. Overfishing, for decades the whipping boy of saltwater environmentalist vegans, is offered as one reason. With fewer nongelatinous fish occupying that sector of the food web, jellyfish seem to be taking over their role, since they feed on the same prey as juvenile and adult fishes. For example, in the Gulf of Mexico, jellyfish feed on commercially important shrimp larvae. And according to a Gulf fisherman, "you can almost walk across the water on them."

A second possibility is higher nutrient levels from agricultural runoff. Jellyfish and their prey can survive quite nicely in eutrophied, oxygen-depleted waters where many true fish cannot.

The third explanation, of course, is the ubiquitous "global warming." Notice that none of the reasons for these jellyfish explosions is natural variability. Surely man has some role; we're simply left with the trivial problem of determining exactly what it is. Still, based on what we've learned so far, the increasing jellyfish population is a problem, right?

The article ends with the following story about Jellyfish Lake on the island of Palau. Allegedly, the 1998 El Niño warmed the lake, wiping out the resident rare golden jellyfish. According to Portland State University scientist Dick Dewey, "The situation was seemingly hopeless." Said Dewey: "Palau's reputation as one of the 'seven biological wonders of the world' has been based on this magnificent lake and its jellyfish" (Add Palau to our summer vacation wish-list! —Eds.).

So how's this for a shocker—when the El Niño ended and water temperatures returned to normal, thousands of tiny golden jellyfish emerged from the lake bottom. What a sight that must have been! They now number more than one million! Is that too many jellyfish or too few? We don't know, but we're guessing Dewey is pleased indeed.

Forgive us for stating the obvious, but El Niños have been going on for a long time, and those golden jellyfish have been living there for the thousands of years since that lake became isolated from the ocean. If they hadn't somehow figured out how to survive slight variations in water temperature, that body of water probably wouldn't be named Jellyfish Lake, now would it? And we're betting the jellyfish boom in other waters is part of a natural cycle as well. Not a sexy explanation, but an ecologically sound one.

Of course, we could simply rename the Gulf of Mexico "Jellyfish Gulf—the 8th Biological Wonder of the World," and then complain in a few years when the jellyfish counts take their inevitable plunge into the abyss.

Reference:

Dybas, C.L., 2002. Jellyfish "blooms" could be sign of ailing seas. Washington Post, p. A-9, May 6.

 

Is a Deformed Frog Better Than no Frog?

Over the past five years or more, stories of amphibians struggling mightily to survive the ongoing climate changes have been standard science-page fodder. Global population declines of frogs, toads, salamanders, and the like, as well as frog deformities (usually extra legs), have been reported in many locations.

A recent study by the University of Wisconsin's Pieter Johnson and colleagues has identified the real culprit—parasitic worms called trematodes. Trematode eggs hatch and infest larva infest snails, where the worms then grow. Once mature, the trematodes burrow into tadpoles, and extra legs can sprout at the burrowing point when the tadpole becomes an adult frog. The deformed frog is then eaten by a bird, and trematode eggs can be found in the bird droppings. According to deformed frog expert Stan Sessions of Hartwick College, "We think the trematode...is increasing its chances of survival by attacking tadpoles and destroying their hind limbs, so they are easier [prey for birds]." These worms are clever, especially considering their rudimentary central nervous system.

So the critical question is, why has there been a boom in the trematode population. It's indirectly caused by fertilizer and cow manure in ponds. High fertilizer levels increase pond algae, and the snail population booms because they love algae. So, more snails equals more snail parasites and more deformed frogs.

It looks like global warming is off the hook yet again. But there are two ironies in this story.

First, based on Johnson's analysis, 80 percent of the ponds with deformed frogs were actually built to water cattle. You guessed it: There would be no frogs there at all, three-legged or otherwise, if we meat-eating, cow's-milk-drinking Americans hadn't built the ponds in the first place! So there are a lot more frogs happily hopping, on two or more legs, than if they were left to their own devices, which are minimal.

Irony No. 2 is that habitat improvements in some regions are attracting more birds such as great blue herons, birds that serve as trematode hosts.

Of course, EPA officials continue to claim that the matter isn't settled and that higher ultraviolet light levels could still be responsible for the increase in frogs. But then the EPA has a long history of ignoring sound science in the promulgation of its own self-interest, so that stance is hardly surprising. That the EPA can't explain why there aren't far more three-legged frogs as you move toward the equator (and UV levels increase) simply means that they haven't yet honed their excuses. (These EPA officials are clever, especially considering their rudimentary central nervous system.)

But this story is a win-win-win situation for environmentalists, EPA officials, and normal people. Environmentalists can campaign against the consumption of meat and cow's milk, the EPA can fret about fertilizer runoff into private farm ponds, and the rest of us can sit back and be amused.

Reference:

Johnson, P.T.J., et al., 2002. Parasite (Ribeiroia ondatrae) infection linked to amphibian malformations in the western United States, Ecological Monographs, 72, 151–158.