Life in the Intertidal Zone: A True Feat

by Gavriel Wolf, Cornell University

To most, the intertidal zone, or what amateurs like myself would call the shore line, is a rocky beach with little more danger than some slippery algae and a whole lot of falling bird poop Through the eyes of scientists who study the intertidal, however, it is a war zone. The algae are armored competitors, and the bird poop is filled with parasites that can puree the insides of a snail.

Lauren Quevillon, who is doing research on a parasite called Cryptocotyle lingua on Appledore Island, one of the Isles of Shoals, guided our group to the intertidal on to get a closer look at her work. As a storm was brewing in the distance, she pointed out a set of shoebox-sized cages holding crabs. As bolts of lighting began to connect the sky and ocean, Lauren hastily explained that the cages were set in the water at different heights, to determine the regions where the parasite was most likely to invade the crab.

The cages that Quevillon originally set are now gone. Lauren spent half an hour drilling two three-inch screws into limestone to hold each cage. She thought, "These things are going nowhere." But soon, a storm came and ripped the bolts out, pulling the cages out to sea. "Now think of what the storm can do to the organisms," Quevillon pointed out. At this point we were not only thinking about the strength of the storm, but we were scared of experiencing it, we ran back for shelter.

Slow and stationary organisms are completely exposed to the elements on the wave battered rocks of the Atlantic shores. On the boulder-strewn shores, there is no sand or loose rock for crabs and snails to find refuge. The tide moves in and out twice a day. While the tide is out, plants and crustaceans must be able to withstand the hot, dry rock, where birds dive-bomb crabs, and snails drill through mussel shells. As the water rushes back in, they must be prepared for an ocean filled with insatiable fish, and the dehydration of salt water.

In addition to the summer waves that tear snails and algae from the rocks, sliding winter ice sheets strip everything except the most robust creatures from surviving on these rocky shores.

The ice sheets are a small reminder of the historical glaciers that gouged out the intertidal shores, between 10,000 and 20,000 years ago. During the last ice age, the sand and pebble beaches were dragged away by glaciers, leaving large rocks in their wake. Only the most daring organisms were left to recolonize the uninhabited shores from New York to Canada.

While the exposed shoreline poses a laundry list of dangers, it also offers a buffet of perks. The constantly undulating ocean delivers food particles to barnacles and other organisms that feed by filtering water. The sweeping water helps algae inhale carbon dioxide and exhale oxygen. Finally, algae sunbathe in the large amounts of energy that shines down uninterrupted by trees or bushes, and reflects off the ocean water.

The variety of opportunities for both danger and growth divides the Appledore shore into zones. The very top of the intertidal only gets a spraying of water, while the lowest regions are almost always submerged. The area in between is a slowly changing continuum of different environments. "The way we tend to describe the intertidal is by the most dominant creatures ", explained Kipp Quinby, a lab preparator on the island.

On one outing Quinby painted a picture of precisely what is happening on the frontlines, where ocean meets land.

The brown line marking the very top of the intertidal, known as the splash zone, is tattooed into the rock by a plant like bacteria. With so little water reaching this region the bacteria are the only sea creatures that can survive

Just a foot or two below the bacteria lays a flattened forest of algae. The long linguini-like plant is about as tough as they come. A waxy surface provides protection against predators, while a death grip to the rock protects it from being swept away by the waves. As we walked along the algae during low tide we heard it crunching underfoot. I was sure it was dead. Quinby explained, however, that the algae does not die, but dries out almost completely as the water recedes, and comes back to life when the water returns.

Underneath the blanket of algae, slightly lower down on the intertidal, the rock is littered with small white mounds of limestone. Barnacles create these bone-like structures. "As a larvae they basically glue their head to the rock," Quinby explained, and build calcium up around themselves for protection.

Barnacles inhabit the middle region of the intertidal where they can out survive the mussel, their biggest competitors for food. As we moved into the depths of the intertidal we could see the mussels amongst a moss-like algae. Mussels stay lower on the intertidal where they will be submerged for a greater portion of the day, to protect themselves from drying out. In order to take control of the zone, mussels will literally sit on top of barnacles, essentially starving them to death.

The intertidal also teems with skittering and creeping crustaceans. Crabs and snails move between zones intensifying the ongoing battle. The snails set up camp in the upper and middle regions of the intertidal, while the crabs reign supreme in the lower and middle regions. It is in this overlap where the true carnage lies. Snails make mincemeat of barnacles and mussels, crabs turn snails into crunchy snacks, and giant Blackback seagulls swoop in and impale the crabs. A littering of snail shells and crab legs are all that is left.

On the battlefield lie Quevillon’s cages. The cages appear to protect the crabs from any ocean dwelling creatures, however the metal wire does little to keep out the microscopic parasites.

The parasite makes seagulls, snails, crabs, and fish the hosts for its lifecycle of growth and reproduction. The process begins and ends in the gulls. The parasite grows to its adult stage in the intestines of the gull and begins a constant production of tens of thousands of eggs. The eggs set up shop in the bird’s poop and wait for deployment. The original parasite dies in the gull’s stomach, while its progeny are launched indiscriminately into the world. With any luck, the parasite-filled feces will land on some seaweed. An unsuspecting snail, just trying to grab a bite to eat, will then ingest a few privileged parasites.

The parasite then moves into the snail’s internal organs where it begins to wreak havoc. After going through a series of life stages, and reproducing asexually several thousand times, the parasite replaces the tissue of the snail’s reproductive organs, effectively castrating the snail. The parasite attack also slows down the snail’s daily activity, in effect stunting its growth and thinning its shell. The snail essentially becomes a robot for the parasite’s reproduction factory.

After going through a complete metamorphosis inside the snail, the parasite pops out as a Cercaria, a two-eyed head with a nutrient filled tail. It must find a host quickly; the tail is like "a boxed lunch, and it only lasts so long", Quinby joked.

Cercaria, too small to see with the naked eye, must find a fish or a crab in an infinitely large ocean. Their odds of survival are next to none. The parasite epitomizes the volatile existence of living in the intertidal. In just one life cycle, they alternate between exponential growth and population crushing destruction a total of five times.

The cercaria that do find a host, form a cyst on a fish or inside of a crab, where it waits for the gull to take the bait. Once inside the gull’s gut, the process starts all over again.

The parasites life cycle may seem like it is only affecting the host organisms. With an aerial view, however, the parasite’s immense impact on the intertidal becomes clear. When parasite populations get out of control large numbers of snails are castrated and crippled, causing snail numbers to drop. The barnacle population, in turn, grows unchecked by one of their primary predators. The expanding barnacle population takes over rock space leaving less room for other organisms such as algae. The ripple effect goes on, possibly changing the framework of the intertidal.

Quevillon’s research focuses on one small part of the parasite’s involved life cycle. She sees her work as helping to paint a more accurate picture of the large implications that this parasite may have on the Atlantic intertidal. Each scientific discovery adds another piece to this complicated intertidal puzzle.

The intertidal is a complex system, where a creature’s daily life is a struggle for survival. This twenty foot wide strip of land is a place that scientists have been studying for hundreds of years, each generation getting a little closer to a complete understanding of the intertidal.

In the last 150 years, with Louis Pasteur’s discovery of life on a microscopic scale, new players have been added to the struggle. At times, scientist seem to have a good grasp of the who, why, and how of the intertidal. With a keen eye and maybe an island full of research equipment, however, the unknown seems to continually assert its dominance.

No Bones About It: New Imaging Technology Lets Scientists See Right Through You

By Celia Smith, Cornell University

The image on the projector screen is eerie and a bit shocking. The ghostly form of a fish swims into view, its body completely transparent except for the pale bones of its skeleton: a moving, breathing x-ray. The graceful interlocking of the carp’s bones pushes it toward some scraps of food. Suddenly, its snout springs forward until the bones in its mouth form a hollow tube. Like a vacuum cleaner attachment, the carp’s extended mouthparts powerfully suck up the scraps, which then float lazily back into its shadowy stomach.

What looks like a marine take on a zombie movie is called XROMM, which stands for X-Ray Reconstruction of Moving Morphology. That’s just a fancy way of describing the creation of three-dimensional x-ray videos to study the symphony of muscle, tendon, and bone that is animal movement.

Until now, there have been many ways scientists have studied how body parts work together to produce all the movements we see in the animal kingdom. Previous research has included examining animal anatomy, and building models. XROMM is unique because it allows scientists to see the individual movements of bones while they are still inside a living, breathing animal.

With this ability to observe natural motion in such detail, scientists have re-created the workings of animal bodies with greater precision than ever before. The carp x-ray video is an example of XROMM’s uncanny ability to capture and display animal movements. It was taken by Nicholas Gidmark, a PhD student in the department of Ecology and Evolutionary Biology at Brown University, who is using XROMM to study the movements of fish jaws.

Jaws evolved in the animal kingdom after an evolutionary split left behind the jawless fish, such as lampreys and hagfish, around 500 million years ago. Since then, most other fish as well as humans have evolved strong jaws with wide ranges of motion. But despite their long history of development, human jaws are built quite simply. "Basically, there are two elements to chewing: the skull and the lower jaw," Gidmark says, "and at the end of the day, there are only so many ways the jaw can move."

Gidmark is interested in a group of animals with much more complex and evolved jaws than ours: the ray-finned fishes. This group of fish, which includes sturgeon, salmon, goldfish, and the carp from the x-ray video, is equipped with heavy-duty mouth machinery that can grasp, bite, and suck with astonishing power. Their many jaw bones and range of motion make them much more difficult to study than humans, and scientists have often had to rely on guesswork to determine which bones do what. Gidmark is now using XROMM technology to look at the movements of individual bones in these fish during the catching and chewing of food.

To create an XROMM image, researchers first take an x-ray ‘video’ of a subject from two different angles. The videos are similar to the x-rays you get on either side of your head at the dentist, only these are recorded as two sets of moving images at the same time. The x-rays capture the images of small metal markers, which have been implanted into specific areas in the bones.

Once the x-rays have been taken, a computer program combines information about the animal’s movements with a three-dimensional scan of its bones. The software uses the metal markers from the video as reference points to match precisely each bone-scan image with its ghostly x-ray outline. The end result is a lifelike image of a real bone, moving around in three-dimensional space.

Scientists can then use computer animation to make the images move around, either to examine how they behave in nature, or to experiment with other possible motions. This ability to play with the images on the computer is important for the scientists, who often find it difficult to get live animals to move the way they want in order to study them. "We use the same computer program Pixar used for Toy Story," says Gidmark proudly. He explains how the program also allows him to view the bone images from any angle, just as though he were a cameraman filming a scene.

To demonstrate, Gidmark shows a clip of a finished XROMM representation. In addition to the x-ray motion shown by the carp, this image displays the bones’ precise shape and pitted texture from the bone scan. The result looks just like a bunch of disembodied bones hanging in space, calmly opening and closing in an unmistakable chewing motion.

Gidmark isn’t the only one who sees how useful three-dimensional x-ray images can be for the study of animals. Henry Astley, also a Brown University researcher, is focusing on frogs. Any casual observer can see that frogs can jump very far for their size; up to six feet for an American bullfrog. Scientists always assumed that the frogs’ leg muscles were responsible for sending it over such impressive distances. But that didn’t always add up, since some frog jumps were estimated to generate up to eight times the amount of power one would expect from muscles alone.

Using XROMM, Astley has been able to show that, in fact, tendons should get the credit for these lengthy leaps. "Think of it like a bow and arrow," says Astley. "If you just throw an arrow, it doesn't go very far. But if you use a bow, you can slowly load energy into the bow and release it all at once. Like the bow, the tendon stores the energy produced by the muscle, then suddenly releases it all at once."

In addition to fish and frogs, XROMM can be used to explore the motion of animals we have never seen move before…like dinosaurs. Even though there are none alive today, artists and scientists can collaborate to re-create their movements, using what we know about their anatomy.

"How does a T. rex run? We can make some good guesses," says Gidmark, who adds that there is high demand from movie makers for this type of imaging. For example, the makers of Jurassic Park and other film producers have developed characters using "motion capture;" a cousin of XROMM technology in which markers are placed on the surface of a subject (such as a model or actor) for tracking movements.

Since motion capture markers are not actually implanted within muscle or bone, copying movements this way is less accurate than using XROMM. However, as entertainment technology becomes more and more sophisticated, XROMM may be introduced to create more lifelike characters.

The precision of XROMM may find its greatest use in human health and medicine. "There are applications for medical and clinical science no one ever though of until about twenty years ago," says Gidmark. The ability to look at exactly how bones and other body parts are working together could be a tremendous help to doctors in diagnosing their patients. For example, x-ray videos of someone walking on a treadmill combined with a bone scan of their leg could help pinpoint the cause of knee pain.

Patients in need of a diagnosis would not be able to wait for metal markers to be drilled into their bones; but without the markers, it is very difficult for scientists to properly match the three-dimensional bone scan images with the x-ray videos. Computer software may become sophisticated enough to efficiently match the images in a "markerless" version of XROMM, but seeing this technology in a doctor’s office is probably still a few years down the road. However, Gidmark believes it has the potential to drastically improve health and medicine, removing a lot of the guesswork from the process of figuring out where it hurts.

Other human uses for XROMM include creating what Gidmark calls a "gold standard" in medicine, meaning that the program could be used to show scientists exactly how a body part should ideally work. For example, if doctors have a standard model for the proper anatomy and motion of human limbs, building comfortable, functional prosthetics could become much easier.
"When we try to build something, XROMM can say: ‘yes, that’s how it moves,’ or ‘no, that’s not how it moves,’" explains Gidmark. In the case of prosthetics, XROMM can help create a standardized computer image of normal human arm movement; flexing, extending, making a fist, and so on. That image can then be used as the template for building a man-made arm that will work exactly like a natural one.

"What I like about this type of science is, it’s more concrete than, say, chemical analysis," says Gidmark. "There’s a bone, and I can see it, but I don’t know what it does." With a bit of luck, and some cutting-edge three-dimensional imaging technology, he soon will.

[Image of carp skeleton courtesy Nick Gidmark]

Two in the Net: How Birders Are Changing The World, One Bird at a Time

by Colleen Cassidy, a recent graduate of Cornell

David Holmes wears his binoculars on a pair of suspenders, speaks in acronyms, and can spot a leaf-colored bird in a tree ten feet away. Holmes holds the rank of Master Bander and works at the Migratory Bird Banding Station on Appledore Island in the Gulf of Maine. His day starts at dawn, when birds are most active. "They wake up and they need to put fuel in the tank," he explains.

He and his team of volunteers catch the birds in mist-nets, which resemble saggy volleyball nets. The nets’ filmy weave, combined with the low dawn light, make them almost invisible to birds, and to people. "Catching yourself is counterproductive," says Lindsay Herlihy, a bander-in-training, "but not always unavoidable."

The first catch of the day is an American redstart, a member of the warbler family. This individual is young, with yellow side spots and a gray back, instead of the adults’ bold black and orange patterning. Holmes gently untangles the bird from the net and brings it back to the lab in a small paper bag.

He rattles off a four-letter acronym and a string of numbers, which represent the bird’s species, and which net it came from. "The first thing we do is to put a band on, so if he escapes and we catch him again, we can get the rest of his information." Tipping the bird upside down, he deftly maneuvers a pair of pliers around the bird’s leg and attaches an aluminum band. The bird cheeps and flutters at the humiliation of his belly-up position, but Holmes has a firm grip. He reads off the band’s number to Herlihy – another string of numbers, each one unique. "It’s like giving the bird a name," Herlihy explains.

Holmes and Herlihy are unlikely to encounter this bird again once they release it. Banded birds, even small ones like this redstart, contain a wealth of useful information. Using the data collected by Holmes and his team, as well as new information obtained by tracking individual birds wearing data recorders, scientists are building a clearer picture of the routes migratory birds use to travel. This picture will have consequences for everyone from airline pilots to wind farmers.

Using the island as a refueling station, migrating birds gorge on the abundant insects and late-summer fruits. The birds store fat that they will call upon as they journey south to their wintering grounds. "With a good fat load, these birds can fly one hundred hours non-stop," says Holmes. "They can cover incredible distances."

Millions of other songbirds will join the redstart on his journey, streaming toward the southern hemisphere in a cloud of feathers and flutters. But exactly how the birds get from Maine to Managua is a puzzle scientists are just beginning to crack.

Using dime-sized "bird backpacks," scientists have recently been able to follow individual birds from the beginning to the end of their migration. Bridget J. M. Stutchbury, a biologist at York University in Toronto, fitted 34 songbirds with the backpacks – packages of equipment designed to detect where the bird was in relation to the sun. Once Stutchbury retrieves the backpacks from the birds, she will use this information to determine how fast the bird was flying, where it stopped to rest and for how long, and exactly what route an individual bird took. This is the kind of information the bird banders had hoped to get by recapturing banded birds "but we almost never catch the other station’s banded birds." David Holmes says.

Holmes is enthusiastic about using Stutchbury’s data to learn about the fate of migrating birds. "The elephant in the room, when you talk birds, is collisions." Collisions between birds and planes happen thousands of times each year – twenty will occur in the time it takes to read this sentence.

According the Bird Strike Committee USA, in 2007 alone over 12,000 bird strikes caused $650 million in damages to aircraft. These numbers were gruesomely brought to life in January 2009, when U.S Airways Flight 1549 made an emergency landing in the Hudson River after two birds struck the engines shortly after take-off. The United States Department of Defense is responsible for mapping airline routes, and knowing the exact routes that migrating birds use will allow pilots to avoid those routes, and prevent similar incidents from occurring.

Migrating birds also face hazards from the green energy movement. More and more countries have been turning to wind power as an alternative to gas and oil for producing electricity. As a result, giant banks of wind turbines have been sprouting off coastlines. Placing the turbines over water puts them in the path of the strongest winds, and also in the path of many migrating birds.

The State of Maine is hoping to install a large bank of turbines just off its coast, but wants to know how those turbines would affect migrating birds. Appledore Island, six miles off the Maine coast, recently acquired a wind turbine in the hopes of reducing the island’s reliance on costly generator power. The State of Maine asked Holmes and his banding team to monitor the turbine for bird collisions, so every morning Holmes walks around the turbine, checking for the bodies of songbirds. "In five seasons of doing this, we have not found a single dead bird," Holmes reports. "except the ones put there on purpose."

Holmes cautions against placing too much weight on their results. "We’re looking at a small turbine that’s on a small island, so you have to be careful applying what we see here to a situation with many, large turbines over water."

Nevertheless, Holmes remains upbeat about the future of wind farming. "There’s an experiment in Mexico right now, looking at the migrating raptors." Each year, thousands of birds of prey fly down the western side of Mexico and cross over to the Gulf of Mexico. "They were seeing 300,000 birds in one day," he says, "it’s been called, ‘the river of raptors.’" The World Bank would like to provide funding to put large banks of wind turbines along the birds’ migration route, "but they have one requirement: whoever ends up running the turbines will have to shut them down completely during migration season."


Holmes is thrilled that non-birders have taken an interest in birds. "We’re finding out pieces of how the world works," he says. And those pieces are rerouting plane and shaping the clean energy movement. Holmes has finished banding and measuring the redstart, and carries it outside for release. The bird leaves his hand, its duty to science finished, its own small piece of the puzzle now recorded and available for future use.

The Island of Science Writing: An Introduction

Appledore Island, located off the coast of Maine, is home to the Shoals Marine Laboratory. The lab is both a school and a research center. Students come by boat to island to spend anywhere from a week to a month taking classes on subjects ranging from shark biology to underwater archaeology. Meanwhile, researchers use the lab as their base of operations for field work and experiments. Students and scientists together work under the watchful eye and the all-day squawking of the island's colonies of gulls.

In August 2009 I came to Appledore to teach a course on science writing. The class was made up of undergraduates, just-graduated students wondering what they were going to do with their lives, and a couple full-time writers considering making a shift of career.

Over the course of the week the students were introduced to the island's intertidal zone, went hunting for hagfish, and visited an archaeological site on neighboring Smuttynose Island, where thousands of years of history is preserved just below the grass. The students then had to write a 500-word piece about each subject.

The students then dove into their final project, a 1500-word story. They could expand one of their 500-word pieces, or take advantage of other stories-in-waiting on Appledore. Some students decided to talk to two teaching assistants who are at the cutting edge of visualizing animals in motion by making 3-D X-ray films. Others chose the bird banders of Appledore, who have banded over 100,000 birds during the migration seasons since 1981. Others struck out on their own, finding stories I didn't even know were waiting to be told.

Science on Shoals is a record of their work. It allows them to complete the journey from research to publication. And it also allows people off the island to enjoy the work of these students and to learn about a remarkable place.

[Update 8/19 8 pm: Changed Appledore to Smuttynose. Thanks, Jim.]