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Light Elements: In the Nose of Jaws

Some parasitic copepods have seizedon a unique piece of ocean real estate.

By Mark Wheeler
Mar 1, 1998 6:00 AMNov 12, 2019 5:15 AM


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Sure you have your Nobel Prize winners, your MacArthur genius awardees, your endowed chair holders at prestigious universities, but give me a scientist that I, common guy, can identify with. Give me a man like George Benz, who will roll up his shirtsleeves and, on any given day, slap the sucking mouth of a lamprey on his forehead to let the tail serve as a windshield wiper for his sunglasses.

Perhaps a sense of humor is necessary when you take a stand that is out of sync with the lockstep of conventional science. Benz rails against ecologists. He fights

the good fight in defense of disease. In particular, he champions the most reviled creatures in the animal world (after politicians)—namely, parasites.

Benz is a fish biologist and the chief research scientist for the Tennessee Aquarium in Chattanooga. While his main job is to oversee health problems faced by the aquarium’s animals, he’s also interested in conservation and natural history research. He’s studied turtles, salamanders, birds, and freshwater mussels, specializing in animals that are native to the southeastern United States.

Closest to his heart, though, are the little aquatic crustaceans called copepods, which live pretty much everywhere it’s wet. Copepods live in salt water and fresh, cold water and hot, shallow water and deep. They live in marshes and bogs. If you’ve ever swallowed a mouthful of water while swimming in a lake or ocean, chances are excellent you’ve quaffed a copepod or two. Bon appétit! If insects are the most abundant animals on Earth, then copepods are the insects of the ocean. Benz goes further, flipping the thinking: I like to annoy entomologists by referring to insects as the crustaceans of the land. These multitudinous copepods live among ocean plankton, thus helping form the first link in the food chain that starts with algae cells, then works its way up to the likes of Charlie the Tuna and Moose and Squirrel.

Benz is especially enamored of copepods that are parasites (roughly 20 percent of all copepod species), so much so that he has lent his name to one: Kroeyerina benzorum. And he is especially interested in those that make their home in and on the ocean’s most infamous predator, the shark. Large numbers and different species of the little cadgers reside in very specific places on a variety of sharks: thresher, great white, hammerhead, and blue, among others. Benz gives a talk about these shark-dwelling copepods, called Putting the Bite on Jaws.

Copepods live on the fins of sharks. They live in the gills of sharks. They live in the noses of sharks, presumably eating shark snot, says Benz cheerfully. They live between the teeth of the great white. We know that a shark’s jaw evolved from a gill, says Benz. I figure this particular copepod thinks it’s still living in a gill. One species of copepod even dangles like an earring from the eyeball of the Greenland shark. At this, told to me over the phone when I was first introducing myself, even I, a trained science journalist, couldn’t help blanching and exclaiming something to the effect of, Yech! Benz, used to such spontaneous outbursts, simply went on talking.

Now, is there anybody who doesn’t hate the thought of parasites, except for Benz and his fellow parasitologists? The idea of wading in some river, say, only to have a little schistosome bore a hole in your leg (guaranteed to inflict the nasty disease schistosomiasis), would give anybody a serious case of the heebie-jeebies. And though modern medicine may be experimenting with leeches to eat away rotting flesh on infected human limbs, it won’t be experimenting on this journalist’s. But as Benz was quick to point out when I visited his lab, from an evolutionary standpoint, parasitism is a wise survival strategy. Further, if it weren’t for parasites, life would not be as we know it.

When he’s not at the aquarium, Benz spends his time in his lab, which is just a short drive across the Tennessee River and down a couple of residential side streets. There he’s carved out some space in a nondescript building that also serves as the warehouse for the aquarium’s gift shop.

Parasites are some of the most successful organisms around, says the 40-ish, bulked-up former competitive weight lifter. From that perspective, pity the fool animal who can’t live inside another animal or a plant. After all, the host for a parasite provides a consistently rich supply of nutrients and a habitat void of predation. Or, as Benz puts it more succinctly, free food and shelter, which, come to think of it, means that my chronically unemployed friend Bob, whose freeloading head is still back in the hippie-dippy sixties, isn’t quite the lowlife I thought he was.

For copepods, parasitism has worked especially well. They’ve lived successfully in their own little worlds for millions of years, says Benz. One fossilized parasitic copepod was discovered in Brazil in 1973, attached to the gills of a bony fish that dated back to the lower Cretaceous, more than 110 million years ago. Benz believes copepods lived even earlier than that. I commonly see copepods that look much more primitive than that fossil, he says. The fact that that fossil is not startlingly primitive, and has some advanced characteristics about it, suggests that copepods go back much further in time, perhaps as much as 400 to 500 million years ago. Now, that’s successful.

We are sitting around a table in Benz’s lab. This is copepod central. On one long wall are shelves that contain mason jar after mason jar of pickled copepods. On a small table are more copepod samples in rusty jars dating from the 1970s, bequeathed to Benz by a retired fellow copepod fanatic. There is a slight aromatic scent of fish and ethanol in the air, rising from sealed plastic buckets stacked on the floor. These contain shark bits—principally snouts and gills—that Benz or his students will eventually dissect in his ongoing research into the copepod life cycle. Biologists study their animal of interest in its habitat, says Benz, so a wolf guy will go to Yellowstone or the tundra, a whale guy to the ocean. My savanna comes to me, he laughs, pointing to the buckets.

Actually, Benz usually travels far afield for his samples. Last summer he went to Australia’s Great Barrier Reef to harvest sharks. One of his students collected specimens in the Gulf of California, off the Baja Peninsula. Benz rarely kills sharks. Generally he tags along with other research expeditions that are netting fish, or with commercial fishermen, who inevitably snare sharks in their nets. You haven’t lived until you’re on the rolling, slippery deck of some boat, standing in a pile of thrashing, half-dead, snapping sharks and trying to get your samples, says Benz. Sometimes sport fishermen will offer to collect copepods for him. I tell them that in a pinch they can pickle the things in good rum or whiskey, he says. Fishermen always seem to know where to get this.

As we chat, Benz pulls mason jars off the shelves and puts slides under a microscope to show me various examples of copepods. There are tiny copepods that look like worms, and bigger copepods that look like more familiar crustaceans. Benz points out one species that’s a dead ringer for Darth Vader. Copepods can range in size from very small, .02 inch long, to as much as 13 inches long, as in Pennella balaenopterae, although this particular species resides not in sharks but in finback whales. On most parasitic copepods, one of the creature’s two antennae is hooked so it can hang on to the host. A mandible rasps at the host’s flesh, while a maxilla sweeps the food to the copepod’s mouth cone.

It’s estimated that parasites make up more than half of all the species on the planet. That makes the other half of us, except Bob, so-called free-living species. It also means that all of us free-livers serve as hosts for these spongers. Humans, for example—if you’re reading this during a meal, hold the chow—can carry more than 100 different critters, a veritable smorgasbord of flagellates, amoebas, and ciliates (all protozoans); flatworms, such as tapeworms and trematodes; lice, ticks, and fleas; as well as nematodes, principally hookworms and pinworms. Most nematodes, by the way, are minute, but Ascaris lumbricoides, a common parasite of humans, can reach a foot or more in length. Yech! But before you start spraying Raid down your throat, consider that many parasites live in harmony with their hosts—that is, they can all just get along. Then again, others carry numerous, frequently fatal, diseases.

Pity the beleaguered shark, then, which carries more types of these pests than humans do. We think of animals that carry parasites as being sick, Benz says, but that’s not necessarily so. He tells me that a blue shark, for example, can carry enormous numbers of copepods—100 on the fins, 4,000 in the gills, and 400 in its schnoz, giving the shark, says Benz, the equivalent of a perpetually stuffed-up nose. In addition, a reasonably healthy blue shark can carry something like 10,000 individual tapeworms, thus becoming what Benz calls a floating hotel for parasites. Each tapeworm, of course, places what Benz euphemistically calls a small tax upon the host but which the nonpartisan might describe as consumption of the host.

Benz got hooked on copepods, as it were, while in graduate school. Although he’d originally wanted to study sharks, his plans were diverted by a course in parasitology he had to take to graduate. It turned out that the parasitologist who taught the course knew more about sharks than anyone Benz had met. That’s when I learned that parasitologists have to know a little bit of everything, he says. They need to understand the anatomy and phylogeny not only of the animal they’re interested in but of its host as well. And they need to understand the environments of both.

That’s his bug about ecologists. Free-living researchers—Benz-speak for biologists who study nonparasitic animals—should be studying the total environment too, but they don’t, he complains. I don’t like to rag on them, but if one-half to two-thirds of all animals are parasitic, it seems as though half the ecologists should be studying parasites. But they’re not.

This is important, says Benz, because the bulk of what we call biodiversity isn’t lions and tigers and bears. It’s the little animals that support all these larger animals. And no matter how small the animal, they all have parasites. Even the parasites have parasites.

In addition, parasites are probably responsible for a lot of the diversity we see in free-living animals. They’ve influenced that diversity through time by the tax they impose. Parasites cause disease and sometimes kill their hosts, Benz grudgingly admits, but that process has surely influenced the gene flow of species by preventing some animals from passing on their genes. The ability to scuffle and sort the genetic potential of their hosts means that parasites have helped chart the evolutionary paths of the free-livers. In other words, parasites have helped shape biodiversity as we know it. So parasites get a bad rap, but they probably shouldn’t, says Benz.

Now hold on a minute. I’m no Mike Wallace, but even I couldn’t help rising to the bait. Don’t parasites have a bad rap, I politely inquire, because they are vectors of parasitic diseases that have been responsible for untold millions of deaths?

Benz grins like a parasite-ridden Cheshire cat. Absolutely! he says, happy that I served up a softball question he can hit out of the park. But disease really isn’t a bad or evil process, he says. All of us have to die in some way. Ideally, we want to live healthy until we’re 102, then die quietly and gently in our sleep. How wimpish and unrealistic. Benz reaches for a mason jar with a giant pickled eyeball inside. Disease is a dialogue between living things, he says. It allows two organisms to exchange ideas and move forward, and it can be a very nonviolent dance. It’s not like predation or an accident, where the process is swift and there’s no communication. Like parasites, disease is an important part of our natural world. Disease, he finishes up, deadpan, is a process that is appreciated only by those who are truly cultured.

We break for lunch, after which Benz regales me with the best parasitologist story I’ve ever heard. (Of course, it’s also the only parasitologist story I’ve ever heard.) It’s the true tale of a young biologist fresh out of Harvard by the name of Jerry who was doing fieldwork in Central America. That’s where a botfly maggot larva took root in his scalp. Removal by scalpel is the best treatment, but surgeons in Central America were in short supply. Jerry’s second course of action was the meat cure—botfly larvae, you see, breathe air through a snorkel-like tube called a respiratory spiracle. Slap a steak on your head and it cuts off the air, forcing the larva to crawl up and into the steak, thereby exiting the scalp. But Jerry didn’t want to shave his hair off, so he adapted to the maggot, waiting until he returned to Cambridge for treatment of the by-now goose-egg-size swelling. There, not surprisingly, he was the talk of the Harvard Health Services clinic, whose services he ended up declining in favor of letting nature take its course. Which it did one night in Fenway Park, as the inch-long larva, probably a Red Sox fan, made its way out of Jerry’s scalp.

We return to Benz’s lab, where he again shows me the large pickled eye. It belonged to a Greenland shark, and, sure enough, there is a copepod dangling from it. A Greenland shark is a large, lethargic bottom feeder. The copepod does blind the shark, but Benz thinks the shark has adapted to its presence.

The Greenland shark lives at depth in the Arctic and probably only needs to use its eyes as light meters, he says. Further, he thinks the dangling copepod may serve as a sort of lure to attract other fish and even the occasional seal, which the shark can then snatch.

It’s finally come time to cut open the schnoz of a shark. As Benz dissects and I watch, I begin to understand his respect for what a complicated little animal a copepod is. As a shark swims, water enters its nose and then hits a back wall. When the water rebounds, it radiates through the olfactory chambers before exiting. While explaining this, Benz squeezes one of the sacs he’s just cut into; copepods, looking like tiny worms, come pouring out. Benz has determined that, in the case of one such copepod, Kroeyerina elongata, larvae enter the shark’s olfactory sac with the inflowing water, then settle on the olfactory lamella (a thin layer of tissue). Like lobsters and other crustaceans, the larvae molt until they achieve adulthood. The males then seek out the females. Once they’ve copulated, the females move to a very specific spot in the outbound water channel. When their larvae have matured, the females’ embryo sacs burst and the new larvae are sent to sea.

Once in the ocean, the larva, which is about the size of the period at the end of this sentence, must find a new host—another shark. Not just any shark, but the same species the parents parasitized. Larvae can’t eat until they do, so the clock is ticking, says Benz. He hypothesizes that the larvae swim to a water-density boundary within a current; since it’s where prey tend to congregate, big predators are attracted. Still, says Benz, think about it—what are the odds that one larva will find the right species of shark just passing by, then make its way to the right spot on or in that shark, in something as vast as the ocean? It’s mind-boggling. It makes our success at putting a man on the moon seem like nothing by comparison.

Benz’s copepod studies have led him to another theory about sharks. I noticed that the copepod taxa in the gills and nose appeared to be closely related, he says, both physically and in the niches they occupy. That made me think that somewhere along the line a habitat shift took place. That, in turn, led him to ask another question. Where did a shark’s nose come from? The answer, says Benz, is it came from a gill.

With his gloved hands dripping ethanol and whatever else oozes out of a dead shark, Benz picks up a diagram of the internal workings of a shark’s gill. Look, he says, see how the anterior and posterior gill arches join at the top? If you take them and turn them, what do you get? He reaches for another diagram of a gill, this one with its insides twisted around. He holds it next to the dissected shark’s proboscis, whose odor is beginning to waft, and not pleasantly. The two look roughly the same. You get a nose? I answer, feeling like a kid on Mr. Wizard. Isn’t that cool? says Benz.

Actually, it is cool, and Benz plans to prove it by doing dna analysis of the copepods in the nose and gill. If I’m right, he gestures happily, accidentally flicking some ethanol onto my shirt, that gives even more value to parasites. Because we can use parasites to study the phylogeny of the host, which allows us to ask the larger questions.

As I dab at my shirt, I realize that Benz’s parasitic proselytizing is going to be a steep, uphill struggle. And I don’t care what he says, I’m not about to let a botfly maggot homestead on my scalp. Still, Benz has helped me develop a respect for parasites. Bob, may you live long and prosper.

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