The stunted growth of coral reefs.

 
New York City shelters its 8.3 million residents within a complex, three-dimensional matrix of concrete and steel. Construction crews must work on the integrity of the city’s structural skeleton constantly just to keep up with growth and age. Like a living organism, the city is expanding up, down and outwards while repairing and replacing decrepit trusses and frames with new, high quality materials.

It is a common big-screen fantasy to imagine the physical decay of New York City if these construction efforts were to suddenly cease in some kind of post-apocalyptic madness. However, the structural collapse that would bring New York City back to nature is actually occurring within nature, and you don’t need CGI graphics to imagine it. Just last week a team of scientists shared new findings that warming oceans are reducing the size and strength of coral reefs in two different parts of the world.

A coral reef is not unlike a city. Reefs are massive underwater edifices that support a stunning diversity and density of organisms. But instead of using building materials like concrete and steel, coral reefs house their residents within and upon a skeleton of calcium carbonate. This calcium carbonate is continually laid down by the reef's construction crew – growing colonies of coral polyps.

Individual coral polyps are actually small, soft-bodied animals that grow affixed to a hard surface. For protection they secrete calcium carbonate near their base. This calcium carbonate accumulates as the polyps grow, clone themselves, and multiply into large colonies. Over many generations, the calcium carbonate left behind becomes the skeleton of the reef, which still consists of a living colony of coral polyps on the surface.

The ability of coral polyps to produce calcium carbonate, called calcification, depends on a host of environmental factors. For example, seasonal differences in water temperature cause calcification to increase in the summer and decrease in the winter, resulting in alternating layers of high and low calcium carbonate density. It creates a pattern similar to the annual growth rings of a tree. The scientists used this pattern to measure the extent of growth and the density of calcium carbonate produced every year by coral colonies. They focused on two genera, Porites and Montastraea, from the Great Barrier Reef and Mesoamerican Barrier Reef. They compared these annual growth data to existing records of warming sea surface temperatures spanning at least a decade.

One of the coral genera, Porites, showed the greatest sensitivity to warming temperatures regardless of location. In both the Great Barrier Reef and the Mesoamerican Barrier Reef, Porites experienced sharp declines in calcification rate as sea surface temperatures increased. If climate change models are correct, at the given rate of decline, Porites in the Great Barrier Reef will stop laying down calcium carbonate entirely by 2100. In the warmer Mesoamerican Barrier Reef, calcification by Porites will cease in 2060. The genus Montastraea has also experienced reduced rates of calcification, although not as extreme. Montastraea in the Mesoamerican Barrier Reef will experience a 40% reduction in calcification by 2100.

The consequences of reduced calcification will manifest differently in the two genera. As temperatures rise, Porites produces calcium carbonate at the same density, but compensates for reduced calcification by not extending as far. Therefore, Porites reefs will grow more slowly and could be outcompeted for space by other organisms. Montastraea continues to extend in warmer temperatures, but it does so at the expense of calcium carbonate density. Much like osteoporotic bones, a Montastraea reef with reduced calcium carbonate density is more susceptible to physical and biological damage. Warming water temperatures will compromise both types of reefs in their ability to support biodiversity, either in terms of space or strength.

As grim as they seem, these predictions are likely conservative. The scientists mention that they don’t consider other factors that affect calcification such as coral mortality, coral bleaching, disease, and the negative consequences of pollution, erosion and other environmental concerns. The slow decline of coral reefs may not be fodder for a disaster flick, but piles of stunted, brittle coral reef will be utterly disastrous for the world’s oceans in a time that is already considered a biodiversity crisis.

Carricart-Ganivet JP, Cabanillas-Tera´n N, Cruz-Ortega I, Blanchon P (2012) Sensitivity of Calcification to Thermal Stress Varies among Genera of Massive Reef-Building Corals. PLoS ONE 7(3): e32859. doi:10.1371/journal.pone.0032859 

Photo: A view of the Mesoamerican Barrier Reef, Belize en.mesoamericanreef.org

The biology behind Facebook.

I developed the following piece at Carl Zimmer's Science Writing Workshop at Yale in February 2012.

It only takes a few minutes on Facebook and a few mindless clicks to get lost in a digital morass of vacation photos, party invitations, and wall posts. No longer is Facebook simply a tool for managing real-life social groups. It has become a platform for a new kind of socializing, where coworkers, acquaintances, and childhood playmates are lumped together in one group of ‘friends.’ These online social networks differ from real-life social networks in more ways than just the definition of friendship. They may actually utilize different social skills. In fact, a team of scientists led by Dr. Ryota Kanai of University College London discovered that this new brand of online socializing taps into different areas of the brain.

The human brain is specially adapted to navigate life in social groups. Scientists even know which brain regions are important for face recognition, empathy, and other social skills because of a recurring pattern between brain size and use. The brain controls the body with cells called neurons, which send rapid chemical signals to other neurons through a web of fibrous connections. Like wires on a switchboard, more connections arise among neurons that signal more often. A brain region that manages a particular skill will actually get larger the more that skill is practiced, because those neurons must form more connections to handle the increased signaling traffic. For instance, as real-life social networks get larger, so does an almond-shaped structure buried in the front of the brain. This structure, the amygdala, allows us to experience and perceive emotions, serving a critical role in managing complex social groups.

While scientists understand the relationship between the brain and real-life social networks, the biological basis behind online social networks remains unknown. Dr. Kanai and his team set out to solve this mystery, asking if differences in online network size can be explained by the size of known social brain regions, such as the amygdala. They predicted that if online and real-life socializing use the same skills, they would see similar trends in brain structure.

More than one hundred UCL students volunteered for the study. Each volunteer provided an MRI brain scan and reported his or her number of Facebook friends, which the scientists call the Facebook number. About half of the volunteers also answered a questionnaire about the size of their real-life social networks.

Using high-tech imaging tools, the scientists manipulated the brain scans, isolating the outer layer of the brain that is used in cognition and information processing – the grey matter. Just like any body part, individual brains are different sizes. The scientists accounted for these differences by adjusting the scale of the images, making every brain the same size. Then they spotted differences in the amount of grey matter found in each of the social brain regions. When they compared these amounts to the volunteers’ Facebook numbers, the results were eye-opening.

The scientists found that social brain regions do indeed get larger as online social networks get larger, but surprisingly, these are not the same regions that help us manage real-life networks. Three regions of the brain, each linked to socialization or memory, were larger in volunteers with larger Facebook numbers. However, the size of other social brain regions, including the amygdala, did not have a strong tie to the Facebook number. As expected, the amygdala was larger in volunteers with larger real-life networks, but the three regions that corresponded to Facebook number were not.

The team’s results suggest that the brain functions differently for online socializing than for real-life socializing. “There is a certain skill for online socializing that these areas subserve,” says Dr. Robert Ross, head of the Laboratory of Neurobiology at Fordham University. But without a strong link to the amygdala, online socializing could be missing the emotional dimension that we experience in real-life. “This may mean that you have developed the facility to distinguish truth from fiction, nuanced expression, all of that. But it doesn’t require any feeling,” says Ross. Dr. Kanai’s research demonstrates for the first time that online socializing is unique on a neurological level, and while it may complement real-life socializing, it’s no substitute for the real thing.


Kanai, R., B. Bahrami, R. Roylance, and G. Rees. 2011. Online social network size is reflected in human brain structure Proc. R. Soc. B April 7, 2012 279 (1732) 1327-1334
Image: detraveler.blogspot.com

Is iridescent fur wasted on the blind golden mole?

Despite human demand for fur coats, mammals are still the dowdiest members of the animal kingdom. While many birds, insects, and mollusks have iridescent coloration that gives off a metallic, shimmering appearance, mammals rely on pigments to imbue their fur with a single, matte color. Biologists think that iridescent animals use their flashy coloration to lure mates. However, a recent discovery of iridescent mammalian fur throws a wrench into the sexual display hypothesis. The iridescent coloration is possessed by a mammal that cannot even see – the blind golden mole.

The golden mole (Family: Chrysochloridae) is a burrowing animal that lives underground in sub-Saharan Africa. It has no need for sight, and its eyes are covered by skin and fur. Despite living in darkness, its dense coat shimmers with green, blue, and violet highlights. Dr. Matthew Shawkey of the University of Akron examined the microscopic, physical qualities of golden mole hairs and found that they are specially constructed to produce an iridescent sheen.

Whether it’s the rainbow shine of a soap bubble or a hummingbird’s shimmering throat feathers, iridescence occurs when light hitting different surfaces is reflected at different angles – a process known as thin-film interference. For these surfaces to shine though, their thickness must be just right. When Dr. Shawkey looked at a golden mole hair under an electron microscope, he found that its outer layer was composed of alternating layers of electron-dense and electron-lucent material. These layers happen to be the perfect thickness to reflect light at angles that produce iridescence through thin-film interference.

Other characteristics of the golden mole hair enhance the iridescent coloration. Instead of a continuous, tubular shape like most mammalian hairs, golden mole hairs become flat towards the ends. This flattened shape, also seen in iridescent bird feathers, provides more surface area for light reflection. Also, the golden mole hairs are smoother than typical mammalian hairs. Most mammalian hairs are covered by rough, cuticular scales that diffuse light. However, the cuticular scales of the iridescent golden mole hairs are compressed and smooth, which focuses more light on the reflective layers.

Like all mammals, the golden mole’s coat is actually composed of two hair types. The iridescent hairs are the protective, outer guard hairs. Golden moles also possess non-iridescent down hairs, which are dense, curly, and provide insulation for the animal. Dr. Shawkey observed that, in contrast to the iridescent guard hairs, the down hairs of the golden mole are thin and tubular with large cuticular scales. While they did not have the layered substructure of the iridescent hairs, their cells had many pigment organelles called melanosomes. The iridescent guard hairs on the other hand contained very few melanosomes.

While iridescence in mammalian fur is an amazing discovery, the reason behind such a trait, especially in a blind animal, remains unclear. Dr. Shawkey hypothesizes that the structure of the iridescent hairs is actually conducive to the mole’s underground lifestyle. Flattened guard hairs may help the moles move through the dirt. Also, the small, compressed cuticular scales likely reduce friction. It just so happens that these adaptations also give the golden mole guard hairs the perfect structure for iridescent coloration. For a mammal that never sees the light of day and couldn’t if it tried, the golden mole’s iridescent fur gives new meaning to ‘beauty is in the eye of the beholder.’

Holly K. Snyder, Rafael Maia, Liliana D'Alba, Allison J. Shultz, Karen M. C. Rowe, Kevin C. Rowe, and Matthew D. Shawkey. Iridescent colour production in hairs of blind golden moles (Chrysochloridae. Biol Lett 2012 : rsbl.2011.1168v1-rsbl20111168. 

Photo: Namib Desert Golden Mole, Eremitalpa granti namibensis. By G. Rathbun, Afrotheria.net

Wetland restoration: Is it worth the effort?

If forests are the lungs of our planet, then wetlands are surely the liver. Wetlands filter overland runoff through a unique suite of plants and soil microorganisms that break down harmful compounds, ensuring that waters reaching streams and coastlines are contaminant-free. Wetlands also store a massive amount of carbon in their soils, serve as a nursery ground for many fisheries, and protect shorelines from floods and storm surges.

Despite these benefits and more, humans allowed worldwide wetland degradation to continue unchecked for two hundred years. Instead of protecting existing wetlands, we gamble on restoration efforts, investing over $70 billion to bring back functional wetlands in North America alone. Until now the overall outcome remained unclear. But after investigating 621 wetland restoration projects around the world, a team of scientists led by Dr. David Moreno-Mateos and renowned ecologist Dr. Mary Power of the University of California Berkeley determined that wetland restoration is generally a losing bet. They published their results last month in PLoS Biology.

The team combed the scientific literature for studies that compare restored and newly created wetlands to adjacent undisturbed wetlands. They compiled all the data from these studies to find out how three characteristics of the restored or created wetlands recover over time: hydrology, biological community, and biogeochemistry.

Wetland hydrology includes water level, flooding patterns, and water storage. It recovers quickly because it depends on the surface features engineered by restoration teams. Before they place a single plant in the ground, restoration teams manipulate soil levels and permeability to achieve ideal patterns of wetland hydrology. The biological community, however, is much harder to recreate. Even after 100 years, biological communities in restored wetlands only recovered to 77% of their undisturbed counterparts. Moreover, plant communities recovered more slowly than animals.

Biogeochemistry, the movement and transformation of nutrients in a system, only recovered to 74% after 50 to 100 years. A healthy, functioning wetland stores large amounts of carbon and organic matter, because their flooded soils deprive decomposing microorganisms of necessary oxygen. If wetlands dry out during a disturbance, oxygen reaches decomposers, allowing them to break-down carbon compounds and larger pieces of organic matter. The decomposers eventually release carbon dioxide to the atmosphere as a byproduct of this process. Once restoration teams restore the proper wetland hydrology, decomposition shuts down and carbon begins to build up in the soil once again. However, even after twenty years, the amount of carbon and organic matter stored in wetland soils remains significantly less than levels in undisturbed wetlands.

Dr. Power's team suggests that restored wetlands do not resemble their original condition because they have shifted to alternative states. Much like building a house, successful ecosystem restoration requires that all the right pieces come together in the correct order. If a construction crew lays out the wrong foundation or neglects to build the second floor, the house will look completely different from the blueprints. The result of this botched construction project is like an alternative state. In ecosystems, the presence or absence of certain organisms determines which organisms come next. If a restoration team fails to introduce an important organism, or does so at the wrong time, a restored wetland may give rise to an alternative state that differs from the goal.

When it comes to wetland restoration, we may know which plant species to add, but the proper foundation remains unknown. Wetland plant communities and biogeochemistry depend on soil microorganisms. If the microorganism community shifts during wetland degradation, or if restoration requires imported soils, the soils may lack the microorganisms necessary for native wetland plants to grow. These unseen changes underground have cascading effects through the wetland ecosystem, producing an alternative state. Alternative states often host different organisms, function at reduced levels, and cannot confer the ecosystem benefits we depend on. Unfortunately, the only way to fix it is to start again from scratch.

Moreno-Mateos D, Power ME, Comı´n FA, Yockteng R (2012) Structural and Functional Loss in Restored Wetland Ecosystems. PLoS Biol 10(1): e1001247. doi:10.1371/journal.pbio.1001247

Photo: Vermont Department of Forests, Parks and Recreation

The ocean's most exclusive community.

The great thing about science is that questions lead to answers. The bad thing is that through this process, a subject that was once novel and strange slowly loses its mystique. When the thrill is gone and the mysterious becomes mundane, the jaded biologist longing for that delicious scientific buzz need only look down - way way down. And, oh my GOODNESS, a really thrilling bit of science was just pulled up from the uncharted ocean depths and published in PLoS Biology.

Deep-sea hydrothermal vents! Is there anything more amazing? They are remote like outerspace but with thriving communities of freaky biota. And as a team of researchers, led by Dr. Alex Rogers of Oxford University, recently found – if you’ve seen one you have NOT seen them all.

These ecosystems are so mystifying because they are fundamentally different from the ecosystems we are used to seeing. Whether you are in tropical rainforest, arctic tundra, or open ocean, nearly all food webs are built upon the plants and algae that harness sunlight to transform carbon dioxide into organic molecules. Photosynthesis is incredible, but also pedestrian. Things get really strange when you look into the darkness and find bizarre organisms that have capitalized on a different energy source – poisonous, smelly hydrogen sulfide gas.

Deep-sea hydrothermal vents, found at an average depth of 2100 meters, spew plumes of hot water from the earth’s crust. This water can be as hot as 400˚C and contains high concentrations of hydrogen sulfide. The surrounding water is nearly freezing and dark as night with pressures so great it keeps the hot plumes from boiling. Still some organisms have managed to thrive in this oppressive environment. Not surprisingly, it all comes down to the microbes. Bacteria and archaea living in and around the vent utilize the energy stored in the bonds of hydrogen sulfide to fix carbon dioxide into organic molecules. This process, known as chemosynthesis, was only a theory until it was observed in action at the hydrothermal vents of the Galapagos Ridge in 1977.

The unusual properties at the base of the vent food web radiate up through all the animals it supports. The giant tube worm that hosts chemosynthetic bacteria within its body is the most familiar image. In many ways it has assumed the role of the community’s iconic species. That is until Dr. Rogers and his team restored the mystique of the hydrothermal vent ecosystem.

Departing from the vents of the tropics and subtropics that are relatively easy to access, the team examined the communities on the East Scotia Ridge (ESR), 500 km to the east of Cape Horn between South America and Antarctica. At a depth of more than 3000 meters in the Southern Ocean, the ESR has two ridge segments with hydrothermal activity, E2 and E9. A deep-sea drive by the remotely operated vehicle Isis revealed that these areas are completely devoid of the tubeworms, polychaetes, clams, and shrimp that we’ve come to expect in hydrothermal vent communities. Rather, they host a complex community of endemic organisms – organisms that haven’t been seen anywhere else – notably a new species of crab, stalked barnacles, limpets, snails, sea anemones, and a seven-armed starfish.

The biological diversity of these areas is built upon the diverse landscape. In some spots chimneys as tall as 15 meters release concentrated plumes of mineral-rich water from the Earth’s crust. This water emerges at temperatures exceeding 300˚ C, and when it hits the near-freezing water of the ocean floor, the minerals fall out of solution and create that black smoker appearance. In other areas there is more diffuse vent flow with temperatures closer to the surroundings. Even between the two sites there is variation in the chemical composition of the vented liquid. These differences could affect the microorganism populations at the two sites which would have cascading affects up the food web.

The truly thrilling thing about the ESR discovery is not the strange biota, because, let’s be honest – finding new species in a remote habitat is old hat. The amazing thing is WHY the species are so strange and why the ESR community is different from the ones we see in similar ecosystems. While they seem inhospitable to us, hydrothermal vents are the only suitable habitat for these organisms. In that way they are just like islands out at sea or parks in an urban landscape. Biogeography is the study of species distributions across space – the traits of an organism that lead it to new areas and the barriers that stand in its way. And remarkably, when you consider all the geologic, hydrologic, and biologic pieces of the puzzle, it appears that hydrothermal vent communities suggest the same patterns of biogeography that govern terrestrial communities.

Deep ocean organisms face unimaginable hurdles to dispersal. Larvae might catch a ride on an ocean current, but many of them won’t last long before passing by another hydrothermal vent. These vents are found only at the boundaries of tectonic plates, which would serve as a great dispersal corridor if they corresponded with the currents. They don’t. Even more daunting is the surface to sea-bed Polar Front, which encloses the Southern Ocean and effectively blocks the entry of outside organisms. At the Polar Front water temperatures and salinity levels change abruptly, creating an insurmountable physiological challenge to most organisms attempting to cross. Knowing this it’s really no shock that the ESR has so many endemic species and so few of the usual suspects. With these barriers preventing migration, the populations of the ESR have been held in reproductive isolation for millions of years with the forces of evolution at work.

However, over geologic time scales ocean currents and plate movements are not even constant, which adds a whole new twist to the story! The hydrothermal vents appeared when the ESR began to spread – around 15 million years ago. That period corresponded with climatic conditions that made the Polar Front less intense, meaning that organisms dispersing from other vent communities actually had a chance to colonize this brand new environment. But the gates closed around 13.8 million years ago when the climate changed and the Polar Front strengthened.

Even more interesting is the phylogenetic history of one of the ESR endemics, which seems to corroborate the geologic and climatic stories. A new species of Kiwa crab, found in the vents of the ESR, is closely related to K. hirsuta of the nearby Pacific Antarctic Ridge. By looking at differences in their genetic markers, researchers loosely estimated that the two species diverged around 12.2 million years ago. Other ESR animals show similarity to species found in hydrothermal vents in the lower latitudes of both the Atlantic and Pacific. The dispersal of organisms from two oceans was likely aided by the Antarctic Circumpolar Current, which circulates around Antarctica, linking the Atlantic, Pacific, and Indian Oceans.

Dr. Rogers' team’s research adds another layer of complexity to the biogeography of vent ecosystems, even suggesting that the Antarctic vents comprise a new biogeographic province. For scientists and non-scientists alike it represents a whole new world of mysteries to be revealed, recharging our hope for big, exciting discoveries.

Rogers AD, Tyler PA, Connelly DP, Copley JT, James R, et al. (2012) The Discovery of New Deep-Sea Hydrothermal Vent Communities in the Southern Ocean and Implications for Biogeography. PLoS Biol 10(1): e1001234. doi:10.1371/journal.pbio.1001234