The strange seahorse tail

The unique mechanics of square – not circular – limbs

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At first glance, the animal kingdom has no shortage of tails. From crocodiles to platypuses, squirrels to pigs and fish to boa constrictors, the shapes, sizes and textures are diverse. But whether flat, flexible, paddle-like, scaly, bare, mighty, curly or fluffy, all tails have one thing in common: they are roughly circular in cross-section. Of all the tails in all the world, there’s only one that differs. And it belongs to the seahorse.

Most people already think that seahorses are fascinating creatures. Their wild colors, upright, single-fin swimming style, fanciful similarity to real horses and the fact that male seahorses get pregnant all contribute to their mystique. But if you take a close look at their rear ends, you might notice another under-appreciated feature. Seahorse tails are curly and muscular. They can wrap tightly around sea grasses, mangrove roots and coral reefs. Uniquely, seahorse tails are square.

Like a cat or dog’s tail – or your tailbone, for that matter – the seahorse tail is formed by a set of vertebrae. However, in seahorses, but not in cats or dogs, each vertebra is surrounded by four, interlocking L-shaped plates (Figure 1). These plates give the tail its unique square cross-section, instead of the circular one characteristic of other animals.

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Figure 1. A computer model of a seahorse skeleton, highlighting the four interlocking, L-shaped plates that surround each vertebra (purple). Photo Credit – Oregon State University.

An Engineering Approach to a Biological Question

So what are the advantages of having a square tail? Michael Porter, an Assistant Professor of Mechanical Engineering at Clemson University, wanted to know exactly that. To find out, he teamed up with engineers from Oregon State University and the University of California, San Diego. The results of their study were published in Science last year.

To determine the advantages of a square tail, Porter’s team decided to examine two categories of tail function: movement and protection. Seahorses don’t use their tails to swim; instead, they use them to grasp objects in their environment while they camouflage to hide from predators and hunt for prey. Flexibility is a key feature that enables these behaviors. In addition, seahorse tails must be resilient – they have to recover their shape after impact. Many creatures prey on seahorses, including fish and sea birds. When these predators decide to take a bite, some structural resilience comes in handy.

Before they could begin experiments, Porter and his colleagues faced a problem. They needed to compare square tails to circular ones, but no circular-tailed seahorses exist in nature. So instead, the engineers created one! They used a special imaging technique called microcomputed tomography to obtain high-resolution, three-dimensional pictures of seahorse tails. Then, they designed a hypothetical tail that was identical, but circular in cross-section. Finally, Porter and his colleagues 3D-printed copies of both tails for experimentation.

The circular tail curled up just as well as the square one. But when it came to twisting, the square tail had some interesting features. The circular tail could twist almost twice as far, and didn’t relax when released. The square tail, on the other hand, had limited twisting abilities and naturally returned to a straight alignment when released. Based on these data, Porter and his colleagues hypothesized that the square tail prevented seahorses from hurting themselves by twisting too far, and saved the animal energy by naturally returning to a neutral position.

In addition, the square tail was more resilient to a simulated bite from a predator. The researchers gave each tail a whack with a rubber mallet, and observed that the square model tail returned to its original shape while the circular one remained partially crushed and misaligned. And when squeezed, the square tail did not change shape but the circular one did. Based on these data, Porter’s team concluded that a square tail might prevent vertebral fracture due to impact or crushing. A square-tailed seahorse would have a better chance of survival after a bite from a predator than a circular-tailed one.

Taking the long view

So what does all this mean for seahorses? Researchers believe that ancient seahorses had stiff, square skeletons that served as protection against predators. Then, they evolved to be more flexible, facilitating hunting and camouflage. But modern seahorses kept the old square skeleton structure, and Porter proved that it’s not just a fashion statement: it allows seahorses to twist and turn without hurting themselves, and provides a suit of armor against bird and fish predators.

 

This post was originally published on Stanford University’s graduate student blog, The Dish on Science.  View the post here.

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Exploring invisible worlds

Modern technology enables real-time observations of the deep ocean.

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The Remotely Operated Vehicle Hercules captured this image of a deep-sea jelly fish just south of a hydrothermal vent on the Mid-Atlantic Ridge. Photo Credit: IFE, URI-IAO, UW, Lost City Science Party; NOAA/OAR/OER; The Lost City 2005 Expedition.

It’s often said that we know more about space than we do about Earth’s own oceans. In the case of the midocean ridges, the maxim is pretty much true. Discovered in the 1950’s, the midocean ridges tower above the seafloor, crisscrossing the globe in long chains punctuated by deep rift valleys. They house the majority of Earth’s active volcanoes, conceal whole communities of undiscovered organisms, and may have dramatic impacts on the global climate. But due to the difficulty and expense of studying the deep sea, explorations of the ridges have been rare.

This year, with funding from the National Science Foundation, the Ocean Observatories Initiative (OOI) aims to change all that. Scientists have outfitted seven different locations on midocean ridges across the globe with hundreds of sensors, cameras and underwater drones, all of which send information back to shore via electronic cables. This month, the data are beginning to pour in, and for the first time in history, scientists can observe the bottom of the sea in real-time, with just the click of a button.

Deep sea change

Over the past 70 years, the relatively few, sporadic studies of the deep sea have overturned long-held scientific theories about the geology, biology and climate of Earth.

At the end of World War II, oceanographers began to map the seafloor in detail for the first time. Instead of a featureless wasteland, they discovered the midocean ridges: mountain ranges collectively long enough to wrap almost seven times around the moon, and tall enough to match the majesty of the Rocky Mountains. These observations helped geologists develop the theory of plate tectonics – informally known as continental drift. They hypothesized that Earth’s crust is composed of a series of thin plates that drift on a hot liquid core, much like rafts on a lake. These rafts can spread apart, collide, or even grind along beside each other.

In the 1970’s, teams of researchers began to voyage to the bottom of the sea in tiny submersibles. They found the anticipated peaks and ridges cut by deep valleys, but they also discovered abundant evidence of volcanic activity. The ocean floor was littered with flows and pillows of lava. The researchers realized that the midocean ridges were volcanic spreading centers: gaping seams in the Earth’s crust, where two tectonic plates were slowly pulling apart. Lava from deep within the planet was rushing up to fill the gaps, forming long chains of low mountains populated by deep sea volcanoes. This discovery helped plate tectonics gain universal acceptance. Terra firma became obsolete.

Then, a subsequent expedition off the coast of Ecuador made an even more fabulous discovery. While exploring near fresh lava, researchers found hydrothermal vents: mineralized towers shooting hot water into the icy sea. And beside the vents, they found life where none should have been. Author William J. Broad records the moment in his book The Universe Below: Discovering the Secrets of the Deep Sea:

“Debra,” a geologist aboard [the submersible] called into a hydrophone, “isn’t the deep ocean supposed to be like a desert?”

“Yes,” came the answer from above.

“Well, there’s all these animals down here.”

The hydrothermal vents were teeming with life: ghostly white crabs and lobsters, brilliantly red shrimps, translucent anemones, hundreds upon hundreds of clams and mussels, and, strangest of all, meter-long tube worms with ruby tips, waving in the water like giant, white-stalked tulips.

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Tube worms (Riftia pachyptila) grow among mussels and anemones in a hydrothermal vent system off the coast of Ecuador. Photo Credit: NOAA Ocean Explorer; Galapagos Rift Exploration 2011.

Alien life

The discovery of life in the deep ocean revolutionized the biological sciences. The predominant view was that the seafloor should be barren and nearly devoid of life. The few organisms dwelling there should be scavengers, taking advantage of whatever food might tumble down from the surface of the sea.

This assumption was very reasonable. Until the 1970’s, all animal life as we knew it depended on the sun for energy. Plants transformed sunlight into food, herbivores ate the plants and carnivores ate the herbivores. The ultimate source of life was the conversion of the sun’s energy to plant matter.

Sunlight cannot penetrate the deep ocean, and yet the profusion of animals there are very much alive. It turns out that animals dwelling near hydrothermal vents form symbiotic partnerships with special bacteria that don’t need sunlight to live. The vents spew warm water that contains numerous chemical compounds, including hydrogen sulfide. Hydrogen sulfide is toxic to most animals, but these special bacteria can transform it into food for their hosts.

Giant tube worms, for example, can grow to be up to 2m long, but they lack a mouth and an anus. To survive, they rely on the bacteria packed inside their bodies. The tips of the worms are red because they’re filled with blood. The blood contains a molecule called hemoglobin, which captures hydrogen sulfide for the bacteria. The bacteria, in turn, use that hydrogen sulfide to nourish the worm. This arrangement, although unfamiliar, works well: Giant tube worms can grow up to 33 inches per year, making them the fastest growing invertebrate species on the planet.

The bigger picture

Recent studies suggest that the deep sea may have dramatic impacts on the global climate.

Maya Tolstoy, a researcher at the Lamont-Doherty Earth Observatory of Columbia University, studies midocean ridges. Her recent paper, published in the scientific journal Geophysical Research Letters, suggests that volcanic eruptions along the midocean ridges are sensitive to the positions of the sun, earth and moon in our solar system. Furthermore, eruptions may have had dramatic impacts on the global climate in the past, and may continue to do so in the future.

Tolstoy has hypothesized that a release of pressure in the deep ocean might trigger eruptions along the midocean ridges, and that pressure fluctuations may occur on regular short-term and long-term cycles. On the short term, eruptions seem to occur about every two weeks, in accordance with Earth’s tidal cycles, which are controlled by the relative positions of the sun, earth and moon. During low tides, when the pressure on the bottom of the sea is weakest, Tolstoy has observed eruptions.

On the long-term scale, Tolstoy noticed that underwater volcanoes have been most active during ice ages. During an ice age, much of Earth’s water is transformed into ice. Sea levels drop and the pressure on the deep ocean decreases, possibly triggering intense periods of undersea volcanism. Just like land volcanoes, deep-sea eruptions release carbon dioxide – a greenhouse gas. A period of deep sea volcanism might provide a natural check, causing Earth to warm quickly after long periods of cold.

Moving forward

If Tolstoy is correct, then midocean volcanic activity will need to be accounted for in climate change predictions. But first, numerous questions still need to be addressed. How much volcanism is there on the sea floor? How much carbon dioxide does each eruption release? Are the eruptions truly influenced by the tides and changes in Earth’s orbit?

Over the coming years, Tolstoy and other researchers like her hope to use the OOI data to answer some of these questions. Among many other things, the scientific instruments on the sea floor will record underwater eruptions and the conditions that cause them in minute-to-minute detail.

Our brief explorations of the deep sea have already transformed our understanding of Earth. Now, with new data streaming in, more discoveries are sure to come.

 

This post was originally published on Stanford University’s graduate student blog, The Dish on Science.  View the post here.

The Birds Revisited

How some of the ocean’s smallest creatures triggered a real-life invasion of crazed seabirds, and helped inspire Hitchcock’s famous thriller

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A sooty shearwater flies over the Monterey Bay. P.C. – Alan Schmierer

In the wee hours of the morning on August 18, 1961, the residents of Capitola, California were awakened by a surreal phenomenon: Thousands of crazed sooty shearwaters were flying erratically through the streets, disgorging bits of fish, and crash landing, kamikaze-like into street lamps and roof tops. A few brave souls ventured outside to investigate, but immediately retreated. The birds, upon seeing the light from their flashlights, flew directly toward them.

The story was front-page news in the Santa Cruz Sentinel by morning. “Residents […] were awakened at about 3 a.m. today by a rain of birds, slamming against their homes,” a bewildered reporter wrote. “Dead, and stunned sea birds littered the streets and roads in the foggy, early dawn.”

A few days later, famed filmmaker Alfred Hitchcock phoned the paper to request a copy of the article. He was researching a new thriller, based on a novel by Daphne du Maurier. Within two years, The Birds hit the silver screen, terrifying audiences across the nation with the story of crazed seabirds pelting the residents of a small, coastal town in northern California.

Experts initially suggested that the sooty shearwaters had been disoriented by the dense fog that had descended upon Capitola that fateful morning. But the true answer, reported over fifty years later by scientists from Louisiana State University in the scientific journal Nature Geoscience, was far more sinister: The birds had been poisoned by tiny marine organisms, called diatoms.

Dangerous Diatoms

Diatoms are tiny, single-celled algae that live in both marine and freshwater environments. The vast majority of diatoms are harmless – in fact, they’re an important source of food for many aquatic animals – but a conspicuous minority produce toxins that can poison birds, marine mammals like seals and sea lions, and humans.

Some diatoms of the genus Pseudo-nitzschia produce a toxin called domoic acid. When plenty of nutrients and light are available, Pseudo-nitzschia can occur at very high densities; these high concentrations of diatoms or other algae are commonly referred to as “algal blooms.” When Pseudo-nitzschia species bloom, shellfish, and small fish like anchovies and sardines, consume large quantities of domoic acid. The toxin does not harm these animals, but it does accumulate in their tissues.

When sea birds, like sooty shearwaters, consume shellfish and anchovies after a Pseudo-nitzschia bloom, the domoic acid poisons them.

The Read Whodunit

In birds, marine mammals and humans, domoic acid acts as a neurotoxin. It interferes with the transmission of nerve signals in the brain, causing lethargy, disorientation, vomiting, seizures, amnesia, brain damage and sometimes death. However, none of this was known during the 1961 attack on Capitola.

It wasn’t until 1991, when similar symptoms affected large numbers of brown pelicans in the same area, that domoic acid was identified as the culprit. Scientists discovered large quantities of domoic acid in the birds’ stomachs, and it was known that they had been eating local anchovies. When scientists looked inside the anchovies’ stomachs, they found large numbers of Pseudo-nitzschia diatoms. The west coast state health departments took immediate action: They closed the shellfish and forage fish fisheries before any humans could suffer the same fate as the birds.

After the 1991 incident, researchers began to suspect that the original 1961 event had also been caused by domoic acid poisoning. However, no one could prove it until 2012, when the Louisiana State research team, led by Sibel Bargu, finally solved the mystery.

Bargu and colleagues examined a number of preserved water samples from 1961, which contained plant-eating zooplankton – tiny ocean predators that partly feed on diatoms like those in the genus Psuedo-nitzschia. They looked in the zooplankton stomachs to see what they had been eating, and found that 79% of the diatoms inside were toxic Pseudo-nitzschia species.

“This […] supports the contention that domoic acid caused the seabird frenzy that eventually led Hitchcock to make his film,” Bargu concluded in her 2012 paper.

The Future of Harmful Algal Blooms

Research on harmful algal blooms – like Pseudo-nitzschia blooms – has accelerated over recent years. However, how and why blooms form continues to be a mystery. Possible culprits include warm water, low wind conditions, and pollution from human homes and farms.

To date, harmful algal blooms have been reported in every coastal state, and the number of these blooms may be on the rise. Just this winter, an exceptionally large and persistent Pseudo-nitzschia bloom occurred off the coast of California, and high levels of domoic acid were found in Dungeness and Rock crabs. This discovery prompted a six-month closure of California’s lucrative commercial crab fishery.

Because of the large economic and health impacts of harmful algal blooms, scientists are working to predict them before they occur. Perhaps in the coming years, the residents of Capitola won’t need a hailstorm of disoriented birds to confirm the presence of a harmful algal bloom.

 

This post was originally published on Stanford University’s graduate student blog, The Dish on Science.  View the post here.

International partnership confirms a new Baja nursery area for white sharks

Conservation & Science

It’s relatively easy to spot when and where a pregnant animal gives birth on land. But in the sea, it’s a whole different story.

Over the past few decades, researchers studying the elusive great white shark have pieced together a picture of their underwater lives: The adults seasonally travel between a remote region of the Pacific Ocean—dubbed the White Shark Café—and their feeding grounds in Central California and Mexico.

But where do females give birth, and where do the offspring grow up?

Researchers in Mexico and the United States, including a team from the Aquarium, have confirmed a new nursery area for white sharks on the Pacific Coast of Baja California.

“We don’t know whether [the sharks] pup in-shore or off-shore,” explains the Aquarium’s Director of Collections John O’Sullivan. “We don’t even know whether they pup in American or Mexican waters.”

But in a paper recently published online…

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The spooky science of shark mummies

Conservation & Science

John O’Sullivan, the Aquarium’s Director of Collections, was in Mexico on a mission. A young white shark equipped with an electronic tag had traveled over 650 nautical miles south from its release point in Monterey Bay, and the tag had popped off somewhere along the central coast of Baja California. The tag contained a complete data set documenting the shark’s movements and physiology since its release, and John aimed to recover it.

Instead his guide, a local fisherman, led John to a shark graveyard.

5-shark-mummies-location-map Location of shark dump site in Baja California, Mexico.

A grisly grimace

Sometimes, commercial and sport fishermen accidentally ensnare juvenile white sharks off the coasts of California and Mexico. But locals in some communities consider it bad luck to discard the unmarketable parts, such as the heads, back into the ocean. Instead, they deposit these shark parts at dump sites in the Mexican desert.

In central Baja…

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Voices for change: Spreading the word on sustainable seafood

Conservation & Science

Twenty food experts—chefs, culinary instructors, media and writers—gathered around a table, brainstorming about what it means to make an impact.

tr16-1171 Blue Ribbon Task Force members swap ideas at Monterey Bay Aquarium.

“Changing minds,” someone called out.

“Inspiring action,” said another.

The 20 are members of the Aquarium’s Blue Ribbon Task Force, a group of 63 culinarians who are actively promoting sustainable seafood nationwide. Each year, a subset of the Task Force meets in Monterey to learn, swap ideas with their peers, and get inspired.

Sheila Bowman, the Aquarium’s Manager of Culinary and Strategic Initiatives, runs the program. “Task Force members come from a variety of culinary fields. They include chefs, educators, food media and others,” she explains.

“What unites them is that they are all the kind of person who speaks out. Rather than just working in their kitchens or at their desks, they’re actually out in public and on social media…

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Our surrogate-raised sea otters are helping restore a wetland

Conservation & Science

Otter 501 meanders through the tidal creeks near Yampah Island in Elkhorn Slough with a dozing pup on her chest. She massages the pup’s rump and blows air into its fur as she makes her way toward a main channel to feed.

To an observer, 501 might look like any other sea otter going about her business. But she’s thriving in the wild today because of a rather remarkable program at Monterey Bay Aquarium.

According to surprising new research, the same can be said of the majority of Elkhorn Slough’s otters.

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Camera to crack a great white shark mystery

Conservation & Science

The idea seemed like a long shot: Build a video camera that could attach to a great white shark for months at a time, withstand ocean depths of more than 3,000 feet, and sense the shark’s movements to selectively capture footage of its behavior.

But Monterey Bay Aquarium Senior Research Scientist Salvador Jorgensen, a white shark expert, thought it might have a chance if he joined forces with the talented minds at the Monterey Bay Aquarium Research Institute (MBARI).

“Some of the engineering team said it was an impossible job,” MBARI Engineer Thom Maughan recalls with a smile. “But I’m attracted to those opportunities.”

So Thom and Sal teamed up on a high-tech mission: to capture video footage of great white sharks in their most mysterious habitat.

Intrigue in the open ocean

Great white sharks cruise the shorelines of the Central Coast, Southern California and Baja California during fall and winter. But just…

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Sea otters are handy with tools

Conservation & Science

What makes people different from other animals? Scientists used to think the ability to make and use tools was a distinguishing characteristic of being human. That changed in the 1960s, when Jane Goodall observed chimpanzees using sticks to fish termites out of mounds. Now, scientists include crows, dolphins and sea otters on the short list of creatures that use tools.

Sea otters dive in shallow coastal waters to collect hard-shelled prey like sea urchins, mussels, abalones, clams and snails. Some of the shells, like the calcium carbonate armor that protects snails, are harder to crack than others—so otters sometimes use rocks as anvils to help break them open.

OLYMPUS DIGITAL CAMERA Aquarium researcher Jessica Fujii tracks sea otters in Alaska. Photo by Nicole LaRoche

Jessica Fujii,  a senior research biologist with Monterey Bay Aquarium’s Sea Otter Program, wanted to learn more. How often do sea otters use rocks and other items? Do some groups of otters use tools more…

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Shark fins, unique as fingerprints

Researchers at the Monterey Bay Aquarium use fins and photography to uniquely identify individual sharks, just like detectives use DNA to uniquely identify people.  Learn more in my recent post for the Aquarium’s Conservation and Science Blog:

Conservation & Science

To most of us, all white sharks look similar: strong, elegant and powerful. But not to Aquarium Senior Research Scientist Dr. Salvador Jorgensen.

“In order to tell them apart, we like to think of something descriptive to call them: Middle-notch, or Split-fin, or Rooster,” Sal says. “There’s one that looks like a profile of Jay Leno. We have a shark called Hitchcock. We have one called Elvis.”

Jay-Leno-Shark When you stare at shark fins all day, you might start to see things – like Jay Leno’s profile.

He pulls up a photo of a  dorsal fin—the characteristic, triangular fin on a white shark’s back that features prominently in movies like Jaws—and compares the negative space at the tip to a profile of Jay Leno. The two are an uncanny match.

Like fingerprints and retinas are unique to each person, a dorsal fin is unique to each white shark. Each…

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