Johns Hopkins Magazine -- November 1999
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Discoveries abound for a lively gorup of 13-year-olds when the Chesapeake Bay becomes their summer classroom.
S C I E N C E    &    T E C H N O L O G Y

Hangin' with the
Blue Crabs

By Joanne Cavanaugh Simpson
Photos by David Owen Hawxhurst

At the National Aquarium in Baltimore, three girls linger at the sting ray pool, watching the regal prehistoric-era creatures cross over each other in a silent, mesmerizing underwater ballet.

As the teens lean over the railing, they glance up at a few people in blue museum volunteer jackets. One volunteer holds a sting ray puppet on her right hand. The volley of questions begins.

"What is in the middle in the deep blue area?"

"How many sting rays are there?"

"Do you make your own seawater?" The girls ask. The volunteers nearby respond in succession.

"I think we once had a whale in there."

"I have no idea."

"I'm not sure."

"That's okay if you don't know," Anne Cunningham, 12, says, reaching out her hand reassuringly. "That's cute," she says, touching the sting ray puppet.

These are smart kids. Among other things, they took the SAT college entrance exam as seventh-graders, nailing 900s or above out of a possible 1600. About 170 were selected by Hopkins's Institute for the Academic Advancement of Youth (IAAY) to attend three-week marine biology camps under IAAY's Center for Academic Advancement.

Anne and her friends, Katie Evans and Rachel Miller, and the other teens will tell you that their test scores land them in the top 2 percentile of their age group nationwide (albeit they say that with a note of irony when they goof up). They're touring the aquarium as part of their summer education--and to take a break from more rigorous coursework.

But even their off-day is unique: they take an under-the-aquarium tour of the control room, talking to staff about life-support filters, the use of ozone to clean the water supply, and stats on the saltwater (30 parts salinity per 1,000, or about 3 percent salt). And, yes, the aquarium makes its own saltwater from scratch.

Pulling out clumps of gravel and weeds, Anne Cunningham (top photo: center; and wielding the shovel), Katie Evns (top photo: right), and other students help bring life back to the last remaining wetlands in Baltimore's Inner Harbor.
The students, mostly 12- and 13-year-olds, don't take notes. But they absorb. And the two primary lessons in their summer study of marine life can be summed up by two quotes highlighted in the museum's displays.

"In Nature there are neither rewards nor punishments. There are consequences." --R.D. Ingersoll

"If there is magic on this planet, it is contained in water." --Loren Eiseley

The lush green campus of Living Classrooms Foundation, with its A-frame buildings, seems more suited to the Outer Banks of North Carolina than downtown Baltimore. But the site along the city's harbor is a nature-oriented classroom for these and other students--including inner city and at-risk youths who study boat building, sailing, job training, and marine ecology. Summer is chaotic here, book bags strewn across the lawn like multicolor mushrooms. In the midday sun, student chants go up: "You put the water sample in, you take the microscope out, you do the hokey pokey, that's what it's all about . . . "

The Hopkins Center for Academic Advancement (CAA), which offers accelerated math, science, and other academic courses to youths, was created four years ago to serve a second-tier of SAT high-scorers--the first tier being those in the Center for Talented Youth (CTY), who are in the top .5 percent of their age group. By contracting with the nonprofit Living Classrooms Foundation, Hopkins CAA directors also hoped to offer a summer program located outside the collegiate venues where it typically offers courses.

This summer, students are housed in former sailors' quarters on a retired U.S. Coast Guard cutter, The Taney, which served in Pearl Harbor and is docked in the Inner Harbor. The chant that goes up among these students is "Pi! Pi! Pi!" The shouted response: "3.14!"

"They come expecting a really good sound academic program, but on top of that what they get out of it is the whole socialization part," says Art Kramer, Hopkins coordinator for academic programs. "They meet kids just like themselves and can feel okay about themselves--they're not the oddball in school. And they make lasting friendships. Now that there's e-mail, they stay in contact over the year."

The CAA-Living Classrooms program started with two courses: Whales & Estuaries, and Oysters. Blue Crabs was offered the next year. This summer, organizers added Marine Physics and Engineering. (In response to a question about where all the cute guys are, Katie sighs: "Physics."). The last course focuses on sail theory and hull construction, with tours of the U.S. Navy hospital ship Comfort and other ships in the harbor.

"The kids get a truer hands-on experience by being out in boats," Kramer says of courses taught by Living Classrooms staff. The students come from all over the country and pay $2,675, or get some scholarship aid, to attend.

No matter what they study here--evaluating the DNA and anatomy of whales, assessing oyster beds in the Patapsco River for diseases, or understanding the life cycle of Maryland blue crabs--the bottom line in the Living Classrooms curriculum is ecology and the preservation of natural resources.

Early one Friday in July, that means restoring the last remaining wetlands in the harbor, a narrow strip of the Living Classrooms' campus across a canal from Bohager's Bar & Grill in Fells Point.

CAA students are slogging around in the muck, wearing black knee-high boots and latex gloves to pick up candy wrappers, Styrofoam cups, and other trash. They note all the dead crabs they find. "That's number 8," Anne says, pointing at a pair of floating claws. She and her counterparts belong to the Crab Group or "The Blue Crabs." Several days with them reveals much about what this marine biology program is about.

Rachel, sunk up to her knees, reaches deep into the muck. Over the next few weeks, she'll be the girl who most often muddies her clothes. Today, while she is walking around in the boots, her socks are soaked with water. And she'll brag about it.

Rachel, Anne, Katie, and the others are here primarily to learn about the beautiful swimmer that is Maryland's most popular seafood--the blue crab, Callinectes sapidus. In the Chesapeake Bay, the blue crab is considered a fully exploited stock; 75 percent of adult crabs are captured each year to supply a hungry commercial market.

The blue crab is a resilient species, but the population is constantly threatened by loss of habitat due to pollution and other causes, as well as overfishing. This wetlands, about 700 square feet along the canal, reveals some of the preservation challenges found in the bay and elsewhere in crab habitats on the East Coast. Trash and choking silt wash down from city streets and parking lots, along with chemicals from farms and suburban lawns.

Rachel Miller dons thigh-high boots to work the weedy waterfront.
The hands-on cleanup is only part of the lesson here. Yanking off boots, the students pull out a wetlands analysis form. They sit down cross-legged on a boat pier, wearing T-shirts, shorts, and shoes with no socks. It's hot, so they crowd into the shade, reading over the questions and writing their answers.

Hypothesize the salinity of the canal in ppt, and the turbidity in feet.

Which of the grasses on the pictorial guide are present in our wetland?

What type of critters would you expect to find in the marsh?

"What do they mean by critters? Any kind of animals?" several students ask.

They will learn that the salinity of the water is 12 to 15 parts per thousand, which means that certain saltwater and freshwater plants and animals can live alongside one another. They drop a secchi disk, a white disk tied to the end of a rope, into the water until they can no longer see it, showing that the turbidity is about two feet. The most prevalent grasses are saltmarsh cordgrass and, in one section, common reed, an invasive, nonnative plant that can choke off other edible plant life. This wetland is important to sustain the critters who live here, the turtles, birds, mud crabs, and blue crabs. The following week the students will weed, remove gravel, and replant the area with native grasses.

It is early in the three-week program and some of the CAA students are more interested in competing than working together. A victorious cry upon figuring out an answer will be followed by an assertion of "I'm not telling you!" And, in what seems to be a difference in maturity in teens of a certain age, the Blue Crab boys, wearing Nike caps turned backward, horse around during their wetlands work, yelling in mock horror at the cleanup job before them, "Child labor! Child labor!"

This story is also a glimpse of youth American style--those borderline teenage years when cynicism and sophistication make up an experimental wardrobe to try on while the kids can still enjoy themselves dancing around in a Ballet to Air-Dry Camp Plates. An age where scientific discovery sometimes takes the front seat, other times the back seat to other kinds of discovery--about themselves and each other.

In the laboratory of Living Classrooms' Weinberg Education Center, the Blue Crabs sit on gray-flecked white linoleum, listening to a lesson about plankton. A few days before, they conducted various lab experiments: studying crab behavior in tanks when food is introduced, and learning how crabs osmoregulate--which involves using their gills and other means to control the amount of salt in their bodies so they can live in waters with a wide range of salinity.

Today, Living Classrooms instructor Chris Rockel Houchens is holding a felt-tipped marker and standing in front of a white board. "Okay, what is plankton and why is it important?" she asks, her wide eyes growing wider in expectation.

"Little organisms that live in a body of water."

"Whales eat them."

"Right, they are a good food source," she says.

Houchens then lays out the various forms of plankton, animal (zooplankton) and plant (phytoplankton). "Okay. So what? Why do we care about plankton?" she asks, drawing a pyramid of the marine food chain on the board.

She pauses. "If plankton die, will we die?" Some students nod. "Yes." Houchens says. "If the plankton die, the food chain collapses."

Soon, the students get a closer look at the bottom of the food chain, trooping outside to an Inner Harbor marina. They dip a dragnet into the brownish water, scooping up microscopic organisms. A metal chain lined with disks is pulled up over the dock, and Houchens and the students scrape off a gooey array of mud crabs, barnacles, mussels, and other brown gunk. This is biofilm, a.k.a "life slime."

Back at the lab, students clump around the samples. Using eye droppers, they squeeze algae-flecked water into shallow slide wells. The goal: view, draw, and identify at least five of the microscopic creatures they find here.

"AAAYYY!" Anne cries out. "I saw something zip across my screen!!"

Houchens peers into a few microscopes, pointing out circles with dots inside and tiny hairs pointing in every direction. "Isn't that beautiful?" she asks.

Bryan Smith, 13, has one eye to his glass. "Wow! It's mutating," he bellows. "It's getting bigger. It's freaky."

The competition has begun anew.

"Oh my gosh," Anne says, tucking loose hair from her pageboy cut behind her ears. "Look at this humongous thing."

"I have a slide full of life," Bryan philosophizes.

"I have a slide full of everything," Anne says.

The slides are swimming with water fleas, filamentous algae, and uncomplicated animals that spend their lives sucking food into simple mouths (colonial bryozoans).

For some students, the discovery--and the personal stake they make in it--is part of the game.

"I have a baby clam!"

"I have a vorticella!"

The biological studies they conduct here are part of nine days they spend at the education center before going out on the Chesapeake Bay for nine days of in-the-field education. While at Weinberg, the students also do water quality surveys, crab ammonia secretion tests, dissections, Internet research, textbook readings, study hall, and reports on what they have learned.

In their downtime, they revert to socializing and begin to bond: playing card games called B.S. and E.R.S. (Egyptian Rat Screw, a student tells me on the side. "You can say the initials but not the name.") Even so, after activity-crammed days, they're calmed down after twilight by CAA resident assistants reading bedtime stories about a cowboy rounding up cows.

Squealing, laughing, and dodging teeth, the CAA kids feed a tank full of bass that weigh almost as much as they do at a fisheries outreach center on the Chesapeak Bay. Hands-on discovery is part of the fun. (L to r) Matt Miller, Anne Cunningham, Becky Cook, Katie Evans. Below the surface: the bass.
On board The Taney one evening, the music from a boom box is cranked up. Rachel, sitting on a metal step in living quarters down below, answers questions about herself. Her straight hair falls out of the ubiquitous ponytail.

These kids exist in a realm far beyond top test scores. And the bios they give out are full of random facts. Rachel lives in Annandale, Virginia--what she calls a vast, sort of pointless suburb. She says her father coordinates the next-generation Internet II research, and that she is the only student who was accepted this year without taking the SATs because she has attended several Hopkins CTY camps, and done well, in the past.

"That's because I'm special," Rachel says. Her camp friends are singing at the top of their lungs to a tape: "Why do you build me up? Buttercup baby. . ."

Rachel is also one of the youngest, going into the 7th grade while the others are going into the 8th. But she has taken Algebra II already, though in science she says they've only studied insects, weather, batteries, and bulbs. She likes bugs. She doesn't eat red meat. "Dead things aren't me." But she will eat other kinds of meat: "I don't feel sorry for all the chickens and turkeys because they are so stupid."

I asked her when her parents first guessed that she was especially smart: "When I was driving home from kindergarten, I asked my mom what a square root was. I had heard it in a joke. When she told me what it was, I figured out the square root of one was one."

A few days later, the CAA students take a school bus to the Days Cove area of Gunpowder Falls State Park. They're going to use their newly learned biological sampling techniques in a man-made freshwater lake and a saltwater tidal marsh.

Using seine and cast nets, they fish for creatures in the bodies of water. They test for PH and salinity, and measure dissolved oxygen, which aquatic animals need to breath via their gills or skin. The science is quick and clean. Answers come fast, and by now terms are second nature. It's just that the fishing part is more fun.

Rachel Miller peers up at a tiny, perfectly formed baby turtle. It's not just science, it's cute. The marine biology program leaves some of the already-seen-it-all teens awed by nature's creations.
Anne is having an especially good time. She just arrived from London, where she lived for two years. Her father works for BP-Mobil and her mother is a corporate marketing and sales executive. While she was in camp, her family moved into their new house in Ellicott City, Maryland. Her brother has a deck off his room, but she has her own bathroom. She is homesick. But she's learning a lot.

"Before I came here," Anne says of the camp, "I wanted to be a pediatrician. Now I want to be a marine biologist. We learned all about different laws, like how Virginia is allowed to dredge for hibernating female crabs [many of which are pregnant]. I'd like to do something to change those laws."

Rachel walks chest high in the water with fellow campgoer, Abby Anito. They pull a net behind them. "We caught a fish! We caught a fish!" Students rush over, stomping through the shallows, scaring away many potential specimens.

Anne comes over: "Awe, he's stuck in the net." She wets her hands as she was taught to do so she doesn't disturb the fish's protective mucous layer, and tries to disentangle the tiny silver fish. "Oh no, I'm going to hurt him." She gently pulls the fish out and plop, he's swimming away.

Another cry goes up. "We caught a fish! We caught a fish!" Everyone splashes over to the other side of the small beach. "It's a piranha," Anne jokes. It's a small sunfish, or sunny, about three inches long. Houchens is excited too. She pulls out a disposable camera to snap a close-up.

The students start spinning off from the net and sneaking deeper into the water, testing the patience of Houchens and the other instructors. The kids gather clumps of brown muck from the bottom and start slinging it at one another. "You guys really want to know what that is?" instructor Liz Diorio asks. "You remember all the organisms we looked at?"

"We know. It's fish crap." The group, mostly boys, answer. "Hey mom. Guess what I did in camp? I swam in fish crap."

Rachel walks out of the water. Her once white shirt is now brown.

Soon after dawn, a group of CAA kids helps Captain Wade Murphy Jr. bait trotlines along Harris Creek. Here to learn about the waterman's life, they watch as Murphy measures the first catches. L to r: James Harris, Becky Cook, Kathryn Woodward, Bryan Smith, and Murphy.
With the land-based part of the program behind them, the Blue Crabs are ready by day 10 to shift to The Mildred Belle, a historic "buy boat" that once carried oysters and crabs to market, and is now a floating biology classroom.

On board are three aquariums with live crabs the students are monitoring. In the cabin below, there's also a poster known as the Crab Contract. Its first two clauses are: Work as a Team and Have fun. No. 7 is LEARN. After that, it sort of falls off: No. 14 Chill. No. 16 Don't throw people off the boat.

Here on the water the students are also learning about the economy of the Maryland blue crab. This means going out early one morning with a waterman, Captain Wade Murphy Jr., who started crabbing in 1955--at age 14. His neck is lined and reddened by decades of sun. A brochure advertising his charter fisherman business notes his "Tilghman Island charm."

He's not in such a charming mood today. As the sky's early morning orange glow fades, Murphy pulls his worn-for-wear work boat, the Miss Kim, to the dock at Harrison's Chesapeake House, where the students camped out on the lawn the night before.

Murphy, who is retired but still runs charters, is here to give the students a bit of the watermen's perspective. For generations, he and others have worked the bay to sustain their families--but they've seen oystering, rockfish harvesting, and other bay livelihoods collapse because of disease, overfishing, and habitat destruction. They blame the state, and each other, yet they still take part in the lucrative blue crab harvest.

Murphy, in a white cap, T-shirt, and blue work slacks, takes the small boat into Harris Creek, just off the Choptank River, a tributary of the bay. The boat passes swans gathered along the grassy shore. He cuts the engine and the Miss Kim, which he named for his daughter, begins to bob and drift.

He starts a motorized roller, and a trotline previously baited with chicken necks rises just above the surface. Murphy scoops with a dip net, flinging crabs into a basket. Katie jumps back. Later he lets the teens try, but in his gruff way barks at Katie because she's an awkward lefty.

Katie grew up in Easton, Maryland, and spent a year living on the water. "That was the best summer," she says. "We had crabs every week." As Murphy scoops crabs, Katie talks about herself a bit more. Her forte is math, too. "My dad is a big math person," she says of her father, who is an anesthesiologist. Her mother is a former nurse. "I've taken Algebra II and I'm going into the 8th grade. This year dad signed me up to do a Johns Hopkins math tutorial in school while the other kids are in math class. The other option was to take me out and put me in with juniors. They are four years older than me. I don't want to do that."

She likes marine creatures. "I wanted to be a dolphin trainer, but now I want to study dolphins," she says, leaning against the edge of the boat. "My dad said, 'Dolphin trainer? They don't make any money.'"

Pass the Old Bay, please...
Fun facts to share with family and friends the next time you sit down to a steaming table full of hard crabs.

A crab-eat-crab world
One of the biggest threats to young blue crabs might be cannibalism. One study found that as many as 90 percent lose their lives to their elders, and biologists believe a good many do expire that way. The larger crabs prey on the young ones and those that have molted and are soft.

Apron clues
Ever wonder, mallet poised, about the gender of the hard crab you're about to dismantle? Check the "apron," found on the crab's belly. Males have a T-shaped apron, while the apron of the immature female is V-shaped; it becomes a "U" in the mature female or "sook."

Two-for-one deal
For the female crab, sex seems to be a onetime affair. But a female retains some of the male's sperm in order to spawn a second time. (And boy, are they prolific, producing between 700,000 and 2 million crabs in a single spawning, though only 1 percent of eggs reach adulthood.) Male crabs can mate several times. And bigger crabs release more sperm.

Bigger by the molt
The lifespan of a crab is two or three years. With each molt, or shedding of its shell, a crab gains about one-third its size.

Salty cravings
Female crabs need to hatch their eggs in water with high salinity, so expectant crabs in the Cheseapeake Bay region head to the southern mouth of the bay; most male crabs are content to remain in Maryland's northern bay waters. The result: Virginia crabbers dredge up a disproportionate number of female crabs, causing a fair amount of distress among their Maryland counterparts, who complain about the declining supply.

Source: State of Maryland

Illustration by Kevin O'Malley

Crabs pile up in the baskets: mostly No. 2s and some big ones: No. 1s. One of the jimmies, or male crabs, is spewing bubbles. Anne conveys some newfound knowledge: "He is trying to produce more oxygen. The way crabs breathe, they suck water that moves over their gills, and the gills take oxygen out of the water." (Later, Anne will tell me with the same assurance that crabs can live a day without their gills when they molt to grow a bigger shell. They can't, but she sounds convincing.)

Murphy, meanwhile, passes along his version of a lesson or two, mostly about the high--or low--politics of Maryland. He talks about the abundance of people who put out industrial-style crab pots, versus the baited trotlines he uses, as being the problem. "This is a bad year; as long as the state of Maryland lets them [crab potters] overharvest and overharvest, we are going to have bad years. It's a damn shame."

Murphy keeps the boat on course with one finger on the wheel, and measures the crabs with a carved wooden stick to check the five-inch limit. The public's taste for crabs has created a market even for small crabs, including immature females. Anne asks him what's the biggest crab he's ever caught. "Not much bigger than that one," he says pointing to a big jimmie. "How the hell, if you catch all the babies, how can they get that big?" he complains, as he pulls in several bushels of young crabs.

This afternoon they'll head out again on The Mildred Belle to the Cooperative Oxford Laboratory run by the Maryland Department of Natural Resources (DNR). As they wait, they gather on a blue tarp, amid piles of sleeping bags and pillows. A few weeks into the trip, the Blue Crabs are closer. Some of the biology lessons are of another nature.

A scattered dialogue goes something like this. A question is posed:

"What was the most interesting thing you learned about crabs?"

"Doubling," James Harris, who is entering the 8th grade, says of the mating ritual.

"That's a 13-year-old boy talking," says fellow campgoer Becky Cook.

James, 13, later says his great- grandfather is Marc Chagall (he also told Bryan he went skydiving when he was 5 years old). There is discussion about the benefits of Victoria's Secret catalogs and tales about celebrities of a sort.

"The only famous person who ever graduated from my high school was in Playboy magazine," Becky says. "How sad is that?"

Becky, also 13, later says that when her parents were notified by letter that she had gotten into the CAA program, they called the school to see if it was a mistake. "Seriously," she says. She says her father is Charles Cook, a political analyst who shows up on Meet the Press. "Now he lets me go to speeches."

They seem to have something on their parents. The conversation switches to how they can change the language on their moms' cell phones into Spanish, Japanese, and Arabic.

These are children of a certain generation. Abby, the flower child of the trip, says that her name used to be Stevie. When she was 2 years old, she says, her parents changed her name to Abby: "I guess they got over their obsession with Fleetwood Mac." Her sister's middle name honors the song Rhiannon.

"If I have two boys, I'm going to name them Bob and Dylan," she later says. "I have a friend named Joplin." After a while, such sporadic conversation grows quiet, and a few nap, the summer sun dappling bare arms.

On The Mildred Belle, the students, wearing faded yellow life preservers, eat lunch: peanut butter and Marshmallow Fluff sandwiches, potato chips, and cookies. As the boat pulls into a dock at Oxford, out walks Keith Lockwood, a burly longtime surfer wearing a white T-shirt, shorts, and sandals.

Lockwood, a DNR outreach specialist, gathers students around several round tanks outside. He tells them how 16 million people live in the Chesapeake Bay watershed. "They contribute to the health and unhealth of the bay," he says.

Two of the bay's biggest problems, he says, are sediment and fertilizer. Because of all the development in Maryland, more sediment is running off and clouding the water, blocking sunlight and coating the bottom. SAV's-- submerged aquatic vegetation-- cannot get the light needed to survive and produce dissolved oxygen. Fertilizer and nutrients from animal waste also wash into the bay, accelerating the growth of algae. The algae then crowd out bay bottom plants and consume oxygen as they decompose each fall.

The result in some areas: "A bay bottom that looks like that parking lot out there," Lockwood says, pointing to the gravelly surface nearby. "Grasses on the bay's bottom are an important habitat. It's important for the blue crabs because it gives them a place to hide."

Blue crabs are one of the few crabs that can swim, and the baby crabs swim all the way up from the mouth of the Chesapeake Bay, where the female crabs winter and hatch their eggs. "They don't have much protection when the SAV beds are not there," Lockwood says, noting the fish and other creatures who eat the tiny crabs. "I like to say, it's like a plateful of chocolate chip cookies in a house full of teenagers."

The teens giggle. Lockwood then tells them about the life cycle of the blue crab, how the crabs are sometimes their own worst enemy, gobbling up each other. He also conveys stories about the terrapins, horseshoe crabs, trigger fish, puffer fish, and giant 40-pound striped bass in his tanks at the fisheries outreach center and lab that's run jointly by DNR and the National Oceanic and Atmospheric Administration (NOAA).

The lessons are many, and some harsh. At one point during the lecture, Lockwood displays a doubler--a jimmie latched onto a female crab, which is known as a peeler because she is about to molt. Watermen like to catch these because they are a two-for-one, and peelers are especially lucrative because they will soon shed their shell and be marketed as soft-shell crabs.

Lockwood tells the endearing tale of the crab mating ritual, in which the male cradles the female for a few days: "How do they find each other? She emits pheromones. It's like 'Hey baby, I'm getting ready to shed my shell.'"

"He cradles her like that until she sheds," he says, showing two crabs linked together on the bottom of a white bucket. "Then he flips her over, impregnates her, flips her back over and cradles her until her shell is hard. Then they basically go their own way." Some crabs don't make it, because it's hard to breathe in this position while molting, and crabs need a lot of oxygen to live.

Later Lockwood pulls the two apart and holds the female up to the light. He touches one of her flippers. "See the red tip?" he asks. "This is a new flipper being formed. She'll shed within 24 hours."

He pauses and picks up a blue plastic trash can with holes in the side and puts it in the tank where other crabs hang along the bottom. He drops her inside the protective can. She sinks gently into the water. "This jimmie can't protect her," he explains of her mate, and points at the four other crabs in the tank. "They'll kill her."

He looks down. "She'll shed tonight, and I'll have soft shell crab for lunch tomorrow." Kids who had been leaning against the tank snap their heads up. A few "Ohs?!" go up.

"Hey, I haven't had a softshell crab sandwich in a long time," he says. "I'm part of the food chain, too."

The game is called Survival--the summer's ultimate lesson and, in the end, the essence of all they've learned.

To play, the teens need to find hidden cards that read "dissolved oxygen (D.O.)" and "habitat," and make a few kills to survive, depending on their position on the food chain.

The players are divided into groups: bio-basic plankton; secondary consumers such as crabs; or higher life forms, represented by sharks and humans.

As the game begins, the plankton fan out into a field on Tilghman Island, looking for D.O. cards in the grass and hiding from predators. Five minutes later blue crabs, horseshoe crabs, and Banded Killifish are given the signal to spread out and find the means to live.

The sharks and the humans, meanwhile, start making deals. "I'll lead the plankton to you guys, but then you can't kill me," says Becky. "Let's gang up on Matt," a female voice says. That's Matt Miller, a blond-haired shark some of the girls have a crush on.

For the next half hour, the teens run around the lawn--dodging, chasing, hiding and hunting, playing a game of evolutionary tag as the sun goes down in a violet bath over the Chesapeake Bay.