Scientist Michael LaBarbera searches for tiny sea creatures—brachiopods—in underwater caves, to help flesh out the evolutionary record.
I am balanced on a stool inside a pitch-dark closet constructed out of black plastic garbage bags, looking through a microscope at something in a tank of seawater. The only light is a faint gleam illuminating my pad and a narrow beam directed on the something in the tank: a sea-creature one eighth of an inch wide that generally lives 100 feet below the surface in coral reefs off the coast of Jamaica. Because this closet is dark and the seawater flows slowly, gently past its shell, and because it has been left undisturbed for two hours, the creature now thinks it is in its natural home. Gradually it lifts its upper shell two millimeters and extends a delicate, fan-like feeding organ. I hold my breath and watch: I am the third person ever to have seen this species of brachiopod (or any species in the genus Crania) in the act of feeding.
“Well, either you’ve fallen asleep in there, or something’s happening.” Michael LaBarbera speaks softly and moves slowly so as not to disturb the brachiopod. But a minute later a truck rumbles by in the distance and the touchy animal slams its shell down so fast it catches a few feeding tentacles in the crack. Then nothing. Once alarmed, the creature may not open again for hours.
(“The phylum Brachiopoda is a small group of animals, all its own,” Michael has explained. Brachiopods make up one of the thirty-nine phyla which comprise the animal kingdom.)
“The stupid brachiopod won't open,” I complain, finally emerging stiff and sweaty into the sunlit laboratory, my sketch barely begun.
“Stupid brachiopod?” Bruce Fouke, a graduate student working with Michael, stares at me and then glances over to see if Michael has heard my words. The work of these scientists is so meticulous and requires such persistence that they seem to have trained themselves never to admit impatience or frustration, never to complain openly. In five days at the laboratory, I have been delighted and astonished by the marine invertebrates being studied here—plant-like gorgonians, sea urchins (Diadema) and the tiny brachiopods—and by the ingenious equipment devised to study them. But I’ve been more amazed by the activity of the research itself, the remarkable persistence of Michael and his students, and their ability to gather valuable data in the face of obstacles that range from torrential rains and leaky roofs to turkey vultures landing on and shorting out the electrical transformers.
Michael LaBarbera, chairman of the Committee on Evolutionary Biology and associate professor in the Departments of Anatomy and Geophysical Sciences and the College, has been studying living brachiopods for ten years, mostly off the northwest coast of North America. He is probably the world's leading authority on the physiology of living brachiopods. His unusual combination of skills and expertise—with fossils, with invertebrate anatomy, evolutionary theory, and biomechanics—helps him come up with questions about evolution that can be answered in a laboratory. Bruce Fouke, a second-year graduate student in the Department of Geophysical Sciences, plans to use his training in geology and paleontology to help him study marine ecological history. After earning an M.S. from the University of Iowa, Bruce came to the University of Chicago to work with Michael on brachiopods, and has accompanied him on this trip to gather data on the ecology of brachiopod populations.
Left: Michael LaBarbera checks a gauge on a flow tank in his laboratory in the Anatomy Building, on campus, zulzile overseeing an experiment by a student. (Photography by Michael P. Weinstein) Right: A brachiopod from the side, in a laboratory tank. Dye is being put into the water from a plastic tube; the dye is carried in currents created by the animal’s lophophore (feeding organ) to and away from the animal. The purpose of the dye is to mark the water flow. By measuring the amount of water pumped per unit in the area of the feeding organ, LaBarbera can evaluate the amount of energy used by the brachiopod. (Photography by Michael LaBarbera)
“Mike applies his knowledge of biology and biomechanics and asks questions that are testable in the modern world,” Bruce explained. “But then he takes it a step further (most biologists don’t). He goes on to apply the same questions—and analogous experimental procedures—to fossil organisms. When you look at a fossil, it’s like having one piece in a picture puzzle, and trying to reconstruct the rest of the puzzle—the physiology and ecology—from that one little piece. Michael’s research will help us find some of the other pieces.”
Three years ago Michael learned that five species of very small brachiopods could be found just off the north coast of Jamaica, near a laboratory famous for coral physiology studies. He applied for, and received, a three-year grant from the National Science Foundation (NSF) to study the hydrodynamics and scaling of these species. He reasoned that if he could show that the smaller species of brachiopod, like the other eight species he’s studied, function as what he calls “minimal organisms,” he could then prove that all living brachiopods (and probably all fossil brachiopods) were minimal organisms. He would thus improve on our ability to interpret the excellent fossil record of brachiopods—and the evolutionary process in general.
Proving that a brachiopod is a “minimal organism” involves measuring its metabolism and its rate of oxygen consumption. But since these animals have the lowest oxygen consumption per unit weight of body tissue of any animal on this planet (and their body tissue weighs less than 0.01 gram, or three ten-thousandths of an ounce) their oxygen consumption can only be measured with an elaborate series of contraptions. These include a polarographic oxygen meter and chart recorder attuned to record oxygen content in water at levels as minute as 0.4 parts per billion.
In September 1984, Michael arrived at the marine laboratory at Discovery Bay, Jamaica, with the oxygen meter, which he’d tested in Chicago and shipped with great care to the lab. In two days it was set up. Michael turned it on—and it broke. The broken part, ordered by phone, and re-ordered and re-ordered by Telex, never arrived. The manufacturer, forgetting Jamaica is in the West Indies, had forwarded each urgent request to a branch in Mexico, where it was duly ignored. Michael returned to Chicago with some exciting findings from his weeks of underwater research in Jamaica. But he had information on not one metabolic rate-the primary purpose of the trip. This meant that in the fall of 1985 he had two twelve-week sessions left in which to do the work of three.
He arrived in October with everything from an underwater movie camera housing to assorted nuts and bolts and dish towels. The oxygen meter is working well this year, but soon after it was set up, both of the lab’s seawater pumps failed, and for two days Michael had to carry buckets up from the dock just to keep his animals alive. Electricity and fresh water are equally unreliable in rural Jamaica. Sometimes there is no water in which to wash equipment. Now something is wrong with the oxygen content of the seawater being pumped into the “wet” lab. Michael hasn't yet decided whether the seawater tanks have been contaminated by bauxite from the breakwater under construction at the lab, but he can tell his results are strangely skewed.
I tag around after Michael, as—outwardly calm—he works on related projects and advises his students, Bruce and his wife, Susan Sponaugle Fouke, a senior in the College who was awarded a grant from the Richter Fund to study gorgonians for her senior honors thesis. As Michael checks a pressure gauge or chases a renegade shrimp around his brachiopod basin—one of the many wide, flat tanks in the lab—he answers my questions.
“Brachiopods have such a superb fossil record that they can tell us a lot about evolution and how it works over very long periods of time. Except that we don’t understand why a brachiopod has the particular shell shape or ornamentation or body size that it does because we don't know the first thing about their biology. Most biologists consider them to be rare animals. They’re not rare. It’s just that they’re not found in the environments biologists typically sample. They’re hard to get to, in underwater caves and in very deep areas where direct access is difficult or impossible.”
Back in the Cambrian age, 550 million years ago, life was just beginning to evolve on earth. The lands were barren, and the seas contained no vertebrates—no fish and no amphibians—just a few worms, crustaceans, and brachiopods. Lots of brachiopods. The fossil record suggests that throughout the Paleozoic era (estimated to be 600 million to 300 million years ago, or approximately half the record of animal life on earth) more than 12,000 species of brachiopods dominated the seas.
Michael has been collecting brachiopod fossils since he was a child. “Where I grew up, near Rochester, New York, you kick the dirt and you’ve found fossil brachiopods. You also find fossil bryozoans and stalked crinoids.” Continental drift has bestowed on western New York rock that, during the Devonian, 400 million years ago, lay in the shallow waters of the Atlantic coast. Today, 340 described species of brachiopods have mostly retreated to deep waters. Michael’s grant originally included a budget to pay professional divers to collect slabs of coral from 180 feet down. But years of brachiopod collecting have given him an instinct for where brachiopods like to live. He was able to find colonies in moderate abundance at thirty to fifty-five feet, where he and Bruce can safely dive and collect specimens themselves. This year he discovered some species in waters as shallow as seventeen feet. “I was decompressing, waiting around, and I thought I might as well look for brachiopods while I waited. I saw a cave that looked like just the sort of place I’d want to live if I were a brachiopod, with lots of cozy niches for brachs to hide in. I didn’t immediately see any—one never does—but I found a slab of coral nestled between two others and chipped it off. Tropical brachs aren’t supposed to live above 100 feet below the surface. Only no one told these guys!”
Michael is determined to collect accurate measurements for body weight and shell length, width, and volume, as well as metabolic rate, for each species. He also plans to dissect a representative number of each species in order to determine the way in which they fold their feeding organ (the lophophore) and to measure its size.
“I should be able to look back at a community of fossil brachiopods and tell you, just from the size of the shells and the distribution of sizes, how much oxygen all those brachs consumed, how much food they needed to keep them going,” he said.
Left: After a dive, Bruce and Susan Fouke have removed their gear, except for depth gauges on their wrists. Right: A brachiopod isolated in a tank in LaBarbera’s laboratory. The open shell indicates it is feeding. This view is from the front; the delicate strands inside the shell are part of the animal's feeding organ, called a lophophore. The animal measures approximately one-quarter inch across. (Photography by Michael LaBarbera)
“Most of the primitive groups—brachiopods and stalked crinoids—seem to be animals that more or less approach a minimal organism. They tend to have low metabolic rates, they tend to be very efficient in their energetic processes, whereas many of the more recently evolved organisms tend to be, in a sense, wasters—they sacrifice efficiency for rate. Bivalves will pump water many times faster than a brachiopod would. You can compare the metabolism of other pairs of animals—say a mongoose, (did I tell you I saw a mongoose here?) and snake—in the same way. The mongoose is a lot faster than the snake when it’s cold outside, but it uses up a great deal of food to keep itself so warm and active. Your average snake can get by on two good meals a year. It takes eighty times as much food to sustain a warm-blooded mammal as it would to sustain an amphibian of equivalent body weight. Brachiopods are an extreme case. By mammalian standards, they are barely alive. I think their commitment to the strategy of maximizing efficiency implies that they probably originally evolved in a situation where that was an important variable—where resources were at a premium. The productivity of the oceans may well have been lower in the Paleozoic.” In other words, there wasn’t much food around: the seas were not nearly as rich in nutrients then as they are today.
Michael feels strongly that it is only by going out into the field and collecting more data that we can put ourselves in a position to ask testable questions about the process of speciation (the production of a new species, or genetically isolated populations). “It doesn’t suffice to come up with an elegant theory to fit known data. The zoologist must go into the field or the lab and take measurements,” he said. Even the very best paleontologists, like Martin Rudwick, professor in the history of science department at Princeton University, may devise convincing theories explaining brachiopod physiology that are not finally supported when the data come in. Rudwick was one of the first to rigorously interpret fossil brachiopods as living animals.
“I’ve been studying the different morphologies of the lophophore—the different coiling patterns—in different species of brachiopods for a number of years now. I was convinced of Rudwick’s hypothesis, that changes in the lophophore coiling pattern occurred to maintain a constant surface-to-volume ratio between the lophophore area and the animal’s biomass as the animal’s size changed. That’s such a nice, elegant theory—and it makes so much sense. What I found was that the various patterns are really ways for the larger animals to avoid having to open their shell so far in order to feed.”
Michael explains that the biomechanics of brachiopods can work in ways counter to our commonsense intuitions, simply because the animals are so small. Very small animals experience the physical world we share with them in radically different ways than we do. They live in a world where gravity is a negligible force and the atmosphere is the consistency of molasses. Sea currents cannot rush past a creature one centimeter high living on a coral reef: that close to a stable surface, water slides by in an orderly, stately fashion—even though it may move ten to fifty times the animal’s length each second. Michael describes the effects of these various forces and of scaling, in his graduate classes on fluid dynamics, biomechanics, and allometry (the measure of the relative growth of a part in relation to the entire organism). He studies organisms as if they were little machines—engineering problems in reverse, as he puts it, where you look at the finished structure—the animal and try to figure out why nature constructed it just that way and what forces, what constraints determined which modifications in structure. In one of his lectures he demonstrates that monsters such as huge insects in science-fiction movies are mechanical impossibilities.
Left: LaBarbera was in a small submarine when he took the photo of stalked crinoids. The crinoids were photographed 700 feet below the surface in the waters off Discovery Bay, Jamaica. The stalked crinoids are about 2.5 feet long. Fossil crinoids have been found measuring ninety feet in length. Right: Susan Fouke films the capture of small animals from water by one of the gorgonians she has brought to the surface. (Photography by Michael LaBarbera)
We stop to look at the flow tank with Susan’s gorgonians, and I make the mistake of asking whether they are plants or animals. “Both,” says Susan, smiling brightly. “Each animal is a colony of suspension-feeding polyps. They feed on the little brine shrimp in the water, but they also contain algae within their living tissues. This animal-algal relationship creates a complex nutritional balance between photosynthesis and suspension-feeding that we still don’t understand very well.” Susan is studying the importance of the flexibility of gorgonian stalks to drag reduction and feeding ability. Why are gorgonian stalks flexible rather than rigid? What’s the advantage to the colony? Does flexibility keep them from being uprooted by ocean currents? Gorgonians are suspension feeders. Like brachiopods, they catch particles of food from the seawater as it flows by them. Susan plans to find out the current velocities in which gorgonians catch the most food. According to Michael, the hydrodynamics of suspension feeding suggests there may be a relatively narrow range of flow velocities over which polyp feeding is efficient. Susan will test this and will learn more about growth rates and how they respond to light.
To study gorgonians, Susan has to collect them from the coral reefs in the same way that Michael and Bruce collect their brachiopods, by diving with scuba tanks. Weather permitting, Bruce and Susan go diving nearly every day. They return around lunchtime, tired and smiling after a morning’s dive, to report new findings—or to report that someone put the wrong gas in the outboard motor, the new battery doesn’t work on the light meter, or sediment ruined visibility at one of the observation sites. I’ve heard enough stories of diving accidents (Michael burst an eardrum last year gathering specimens) to be happy I can’t participate in these adventures.
I do have an opportunity to accompany the divers in their boat, however. We set out—Bruce, Susan, Michael, a lab technician named George, and I—at 8:30 the next morning, after loading the boat with flippers, rubber socks, gloves, masks, depth gauges, four sets of tanks, underwater magnifiers (made by Bruce), three cameras, two buckets, and water-proof slates and pencils. The weather is perfect. The divers are eager to get to their sampling site at Rio Bueno before the day’s breeze picks up. As we approach the site, smooth swells are moving across the bay; looking over the side of the boat, I can see almost to the bottom, forty-five feet down—bright patches of sand, and the duller coral reef. The divers are all suddenly beaming at each other, elated.
“You can come along any time!” laughs Bruce. “You’ve brought clear water. Look at this!”
Susan asks if I get seasick. George says it’s too calm for seasickness, but later, after half an hour in the bobbing boat has undone me, I am glad to have been warned. My cure for the motion sickness—singing at the top of my lungs—puzzles a Jamaican fisherman who glides by in a slender wooden canoe, his dreadlocks piled into a loose knit cap, his eyes curious, guarded.
Michael heaves the compressed-air tank onto his back and falls off the boat backwards into the water. Bruce and Susan put their tanks on in the water. Either way, the putting-on of gear reminds me of medieval fighters donning armor. In a shimmer of bubbles, they are gone below the surface. They will stay down for about forty-five minutes, including the time they need to “decompress”—to let the nitrogen that has been squeezed into their blood and tissues at the higher pressure seep out slowly. Otherwise it will form potentially deadly bubbles in their blood.
Earlier in the month, Bruce had volunteered to spend an evening in the decompression chamber with an accident victim, so even though he’s never had a diving accident himself, he has gone through the stress, claustrophobia, and actual physical danger of five hours in a high-pressure cell that measures seven feet long and three in diameter. Just looking at the steel furnace-like compression chamber, with its many valves and one small window, gave me the creeps. But Bruce combines an intellectual understanding of the danger with calm, cheerful confidence. “The only hard part about scientific diving,” he told me, “is that your mind thinks as if you're on land, but you’re under a lot of physical constraints because you’re on scuba. So you’re trying to think, O.K., let’s see, those animals are sixteen centimeters apart; but then at the same time you’re thinking, I’m at sixty-two feet, I have thirteen minutes left, I have this much air. You’re always planning. You have to organize a complete dive-plan before you get anywhere near the water, and then while you’re concentrating on your work, you have to remember to keep following your plan. You can’t get caught up in the research and stop thinking about where you are. Your top priority always has to be safety.”
No smart diver, given a choice, would prefer to dive in a cave. But brachiopods live in caves, so that is where Michael and Bruce dive most of the time here. They have to find the cave, enter it, take measurements and remove samples in the limited time it is safe to work at thirty-five feet. If the wind picks up and a current clouds the cave, or if any equipment stops working, that’s it for the day: you can’t come back and finish up after supper.
Collaboration is crucial in scientific diving; ideally, three or four go out in the boat together. Bruce can take light measurements while Susan records them. Susan can select the species of gorgonians she wants to study, and Bruce can help her test them. At the same time they are double-checking each other’s time and are ready to help each other if anything goes wrong. Bruce always carries an “octopus rig”—an extra regulator—on his tank. If Susan’s regulator were to fail, or if she were to run out of oxygen, she would be able to breathe from his tank.
After lunch (I’m disappointed with breadfruit—it tastes like Wonder Bread), Michael is back in the lab working with the chart recorder. Inside a small, watertight Plexiglas chamber, complete with water-stirrer and gold polarographic oxygen sensor, sits one diminutive brachiopod (genus Lacazella). Michael lowers the chamber into a bath of water attached to a circulator and control that keeps the temperature constant within one-hundreth of a degree centigrade. This, too, is covered with black garbage bags—except for a peep hole, through which we watch to see when the brachiopod will relax and open up. Michael explains that the sensor works by measuring the amount of oxygen in the layer of water right next to the gold electrode. As the brachiopod metabolizes oxygen, the stirrer ensures that the level of oxygen is more or less constant throughout the chamber (and keeps the brachiopod happy by mimicking natural currents), while the sensor, attached to the chart recorder, keeps track of every change in the oxygen level.
I ask if there isn’t an easier way to get these measurements. “Yes, there are four,” says Michael, and he goes on to explain why each of the four would produce results less reliable than those from this system. I absorb about a fifth of what he’s telling me; meanwhile, being careful not to bump anything or move quickly, I peek in at the brachiopod on its Plexiglas throne.
“Is it open?” he asks.
Two weeks ago Michael discovered a new species of brachiopod, in the genus Discinisca. Last week he managed to dissect brachiopod brood sacks out of the Lacazella and release the embryos, which promptly began swimming around, looking for an appropriate substrate for attachment. This week he and Bruce discovered what eats brachiopods—sea urchins. “We have the first known predator for brachiopods. We found that Diadema will eat brachiopods in the lab, and recovered pieces of brachiopod shell from their feces. Now Bruce can dive for Diadema by the cave, and we’ll see if we can find brachiopod shell remains in the guts of animals in their natural environment. That will be conclusive proof. We may have the explanation for why brachiopods live only in deep waters—where the sea urchins don’t go—or in caves, where they can’t
These findings are exciting. But at my last dinner before the flight back, the answer to my question, “Will you get the metabolic rates you need?” is still “I don’t know.” Part ofthe energy with which Michael has just hand shredded an entire coconut for the goat curry he’s preparing is clearly nervous tension. Bruce, Susan, Michael, and I enjoy the curry by candlelight and mosquito-repellent coil out on the veranda overlooking the bay. The view is breathtaking, but it includes the lab where something is still wrong with the seawater. Michael’s pet damselfish is sick. He now thinks the seawater intake system must be sucking in bauxite from the breakwater. It’s not that the measuring mechanism is off; the oxygen content of the seawater in the lab has changed.
I find it odd to be on a tropical island listening to the night calls of gekkos as the moon reflects off the water below, eating fresh pineapple, sipping rum and tonic, and worrying about the oxygen content of some seawater tank. Michael looks tired. He has two more weeks—assuming the power and water pumps don’t fail—in which to solve the water problem, record his data, and pack up. Bruce raises his glass of fresh soursop juice (a local delicacy that tastes like strawberries) and toasts to a safe return to the States—for all of us.
Mail from the Caribbean is extremely slow. Three weeks later, after Michael, Bruce, and Susan have returned to Chicago, I receive an airletter from Discovery Bay: the jeep has broken down again; some tourists were badly stung by sea wasps; a doctorbird flew into the lab and had to be handcarried to safety. The damselfish who’d snatched bits of snail from my hand—died, but Michael has succeeded in modifying the experimental procedure so that the chart recorder makes sense again. He now, finally, has accurate figures for metabolic rates of four species—enough to show NSF that he has a proven system all set up for next year. “Bruce did catch those Diadema, and Susan’s work goes very well, too. I really think if she had one more week here, she’d have enough material for a master’s thesis. We are scrambling to finish up and get packed: I’ve taken some pictures of Bruce and Susan that you might be able to use in your article. Hope they come out.”
Maggie Hivnor, AM’77, is the paperback editor at the University of Chicago Press.