Phragmites australis, the common reed, has been a component of North American marshes for thousands of years. However, a novel genetic lineage, Phragmites australis australis, found its way to North America sometime in the 1800s, scientists believe, probably hiding in plain site as discarded packing material. Its next decades were then spent quietly growing in estuaries and coastal marshes in North America, a minor player in the community of marsh plants, attracting little more than passing notice by wetland scientists.

Suddenly, some 20 years ago in a Jekyll-and-Hyde-like scenario common among invasive plants and animals, this once humble reed “just took off,” says Patrick Megonigal of the Smithsonian Environmental Research Center in Edgewater, Md. Today it is an aggressive invader pushing into the tidal and non-tidal wetlands of North America and vigorously replacing native plants, including its very close native genotype Phragmites australis americanus.

Image above: Ecologist Thomas Mozdzer, former Smithsonian Post-Doctoral Fellow, works beside a patch of invasive Phragmites australis at SERC’s Global Change Research Wetland. There, scientists are manipulating CO2 and nitrogen levels to mimic the world of 2100 if climate change continues as expected. (All photos courtesy of SERC)

Now, a new study by Megonigal and lead author Thomas Mozdzer of Bryn Mawr College, that takes a close look at the biogeochemistry of this invasive plant and its native North American counterpart, reveals how a subtle genetic difference in the lineage of a plant species can have a major impact on greenhouse gas emissions.

The scientists found that invasive Phragmites emits much higher levels of methane (CH₄) than native Phragmites, and both emit more methane when grown under predicted future levels of atmospheric carbon dioxide and nitrogen. As methane is a principle greenhouse gas, these findings, Megonigal says, have the potential to negate the use of tidal wetlands inundated with this invasive reed as an asset in carbon offset credit systems.

Image above: Native and Introduced Phragmites: Native Phragmites (left) and invasive Phragmites (right). The invasive strain of Phragmites australis from Europe is one of the most rampant plant invaders in the eastern U.S. It can grow up to 15 feet tall and monopolizes light and nutrients, preventing any other plants from surviving in its shadow.

“Tidal wetlands store carbon at very impressive rates that are comparable to a rainforest,” Megonigal explains. “They take carbon out of the atmosphere as carbon dioxide (CO₂₎ and turn it into biomass that ends up being stored in the soil as roots or detritus, which is good for the climate. The flip side is that these systems also emit methane.” Overall, however, there is a balance of carbon intake and methane emission in many native tidal wetlands that equals a net benefit for the climate.

Not necessarily so with Phragmites australis, Megonigal says. “When Phragmites australis invades, it has the potential to upset this balance by increasing methane emissions.” Higher levels of atmospheric carbon dioxide and nitrogen also made this plant much more vigorous, a related study showed.

This information is important for people interested in using protected wetlands as credits in carbon offset systems. In order to comply with agreed upon limits to the amount of carbon dioxide they are permitted to emit, governments and companies can buy, sell and trade these credits, which can take the form of protected forests, wetlands and other natural areas that hold or sequester large amounts of carbon.

Image above: Native Phragmites (left) and invasive Phragmites (right). The invasive strain of Phragmites australis from Europe is one of the most rampant plant invaders in the eastern U.S. It can grow up to 15 feet tall and monopolizes light and nutrients, preventing any other plants from surviving in its shadow.

“Invasive Phragmites does not have the potential to vastly increase the emissions of methane globally,” Megonigal points out. “The increase in methane that we are experiencing today is mostly due to anthropogenic sources.

“Still, we suspect that as the climate changes natural sources of methane emissions will begin to increase for a variety of reasons. Our paper shows that one of those reasons could be the introduction of new, novel species that support higher rates of methane production.” –John Barrat

“Increased Methane Emissions by an Introduced Phragmites australis Lineage under Global Change” appeared in the journal Wetlands in May 2013.

Soon after a dirt road through the forests of Lambir Hills National Park in Borneo was improved in 1987, local markets selling the meat of wild animals expanded dramatically. By 1994 biologists observed that a bird known as the helmeted hornbill had vanished from the park and other species—such as the rhinoceros hornbill, the Bornean gibbon and the sun bear—had become extremely scarce. A survey conducted in 2004 found that more than 20 percent of the mammal species and 50 percent of the bird species in the park had vanished.

Rainforest at Lambir Hills National Park in Borneo. (CTFS photo by Christian Ziegler)

Now, a new study published in the journal Ecology Letters spotlights the impact the loss of these animals is having on the forest itself. Using census data from trees growing in a 52 hectare (128 acre) plot in Lambir monitored for 15 years just after the onset of intense hunting, the researchers found a marked increase in crowding of saplings beneath tree species that depend upon animals to disperse their seeds.

“Tree species that use these animals to disperse their seeds have lost the ability to displace offspring far away from the parents,” says study co-author Matteo Detto, of the Center for Tropical Forest Science, Smithsonian Tropical Research Institute. “For this reason these species appear more aggregated or clustered compared to when hunting was not present.”

A selection of seeds from Lambir Hills National Park, many of which are dependent upon animals for their dispersal. (CTFS photo by Christian Ziegler)

Fruit that would formerly have been eaten by hornbills, gibbons and other animals and dispersed far and wide now simply fall to the ground and sprout under the maternal tree. Due to overcrowding these saplings suffer high mortality. The result, the study shows, has been a small but consistent decline in local tree diversity, an effect the researchers expect will become more pronounced over time.

“Lambir is the richest forest in the whole of the Old World tropics, there’s nowhere else in Asia or Africa that has a forest this diverse in tree species, with some 1,200 tree species growing in an area of about 125 acres [the CTFS survey area],” explains Stuart Davies, director of the Center for Tropical Forest Science and a co-author of the study. “Lambir is a tiny little national park and unfortunately what’s happening in the tropics is that many of these conservation areas have become isolated by agriculture of various kinds. In the case of Lambir it is surrounded by oil palm plantations and by a growing urban population. These isolated conservation areas have no future for surviving  if they continue to get hunted in the way they are. The great majority of tree species need vertebrates for their dispersal and most of the big vertebrates are gone.”

The study showed that overhunting of large seed-dispersing animals caused “the spatial distribution of the forest trees to change in a way that could dramatically change the composition” of the forest, says Tania BrenesArguedas, a co-author also from the Center for Tropical Forest Science at the Smithsonian Tropical Research Institute. “It was very impressive that such changes in distribution and survival could be detected in such a short period of time.”

Hylobates mulleri, or Muller’s Bornean gibbon

Among trees with animal-dispersed seeds, species with medium or large seeds had significantly lower success in sprouting new seedlings than species with small seeds. Trees that use other methods of dispersal, such as wind, gyrations and seed projection, did not show greater clustering.

“The situation at Lambir is increasingly prevalent throughout tropical Asia,” the researchers write, “and in other tropical areas with high human populations and a relatively low proportion of remaining forest, including West Africa and the Atlantic forests of Brazil. Moreover, as access improves we can also expect increasing levels of defaunation [overhunting of animals] in remaining large blocks of rain forest, such as the Amazon and Congo, unless the process is countered by strong conservation measures.

“Enhancing the protection of wildlife and restoring animal populations where they have been depleted will be essential for prevent a substantial decline in tree diversity in these forests.”

(The Center for Tropical Forest Science is a global network of forest research plots committed to the study of tropical and temperate forest function and diversity. The multi-institutional network comprises more than 40 forest research plots across the Americas, Africa, Asia, and Europe, with a strong focus on tropical regions. Through regular surveys CTFS monitors the growth and survival of about 4.5 million trees of approximately 8,500 species.)

The paper “Consequences of defaunation for a tropical tree community,” was conducted by scientists from the Chinese Academy of Sciences, the World Agroforestry Center, and the Center for Integrative Conservation in China; the Center for Tropical Forest Science, Malaysia; the University of Pennsylvania, the Smithsonian Global Earth Observatory, the Smithsonian Center for Tropical Forest Science, the Smithsonian Tropical Research Institute, and the World Agroforestry Centre, Osaka City University in Japan. --John Barrat

Maintaining natural movement of animals that live in the tropical rain canopy in South America is important for the health of the ecosystem. As development and resource extraction encroach on remote areas of the Amazon, the forest is becoming increasingly fragmented, limiting where animals that cannot fly and only live in trees can go. To find a solution, researchers at the Smithsonian Conservation Biology Institute convinced a development company to do an experiment. Researchers worked with company engineers to leave behind “natural canopy bridges,” standing trees with large branches that maintain connections between both sides of the forest.

Previous global warming events led to more diverse tropical forests. This is a view of the lowland tropical forest on Barro Colorado Island in Panama.

South American rainforests thrived during three extreme global warming events in the past, say paleontologists at the Smithsonian Tropical Research Institute in a new report published in the Annual Review of Earth and Planetary Science. No tropical forests in South America currently experience average yearly temperatures of more than 84 degrees Fahrenheit (29 degrees Celsius). But by the end of this century, average global temperatures are likely to rise by another 1 F (0.6 C), leading some scientists to predict the demise of the world’s most diverse terrestrial ecosystem.

Carlos Jaramillo, Cofrin Chair in Palynology, and Andrés Cárdenas, post-doctoral fellow, at the Smithsonian in Panama reviewed almost 6,000 published measurements of ancient temperatures to provide a deep-time perspective for the debate.

“To take the temperature of the past we rely on indirect evidence like oxygen isotope ratios in the fossil shells of marine organisms or from bacteria biomarkers,” said Jaramillo.

When intense volcanic activity produced huge quantities of carbon dioxide 120 million years ago in the mid-Cretaceous period, yearly temperatures in the South American tropics rose 9 F (5 C). During the Paleocene-Eocene thermal maximum, 55 million years ago, tropical temperatures rose by 5 F (3 C) in less than 10,000 years. About 53 million years ago, temperatures soared again.

According to the fossil record, rainforests prospered under these hothouse conditions. Diversity increased. Because larger areas of forest generally sustain higher diversity than smaller areas do, higher diversity during warming events could be explained by the expansion of tropical forests into temperate areas. “But to our surprise, rainforests never extended much beyond the modern tropical belt, so something other than temperature must have determined where they were growing,” said Jaramillo.

Jaramillo and Cárdenas’ report also refers to findings by Smithsonian plant physiologist Klaus Winter that leaves of some tropical trees tolerate short-term exposure to temperatures up to 122 F (5 C). When carbon dioxide concentrations double, trees use much less water, which is further evidence that tropical forests may prove resilient to climate change.

They’ve got no roots or veins and grow in hanging pendants or tightly packed mats attached to stones, soil and wood. Called by some “the secret plants that surround us,” the bryophytes (mosses and liverworts) were the first plants to colonize dry land 475 million years ago. Today more than 26,000 bryophyte species populate the earth.

Now, a recent experiment with a number of tropical species of bryophytes in western Panama suggests that some of these plants may be able to adapt to the warming temperatures that global warming will bring.

Tropical moss of the species Leucoloma cruegerianum can bee seen growing to the right on this branch at a study site in western Panama. (Photo by Sebastian Wagner)

Researchers from the University of Oldenburg, Germany and the Smithsonian Tropical Research Institute in Panama, collected 15 individual plants each of 9 common species of bryophytes found growing at cool higher altitudes in the tropics and transplanted them at lower altitudes where temperatures were an average of 2.6 to 3.6 degrees Celsius warmer.

In the tropics bryophytes are scarce in the warm, drier lowland areas but prolific in higher mountain areas where temperatures are lower and the humidity is higher. As botanist Gerald Zotz, of the University of Oldenburg and the Smithsonian explains, a bryophyte’s survival is a balancing act between its daytime intake of carbon during photosynthesis and its nighttime loss of carbon through respiration. This balance is dependent on temperature and humidity.

Specimens of pendant mosses of the Frullania species hang from wires in a study plot in western Panama. (Photo by Sebastian Wagner)

Higher temperatures and dry conditions can reduce daytime photosynthesis in bryophytes, leading to lower carbon intake. Warmer, dry conditions also increase carbon loss at night through higher respiration rates. (Earlier studies have shown that at optimum temperatures bryophytes lose at night on average 60 percent of the carbon they gained the previous day.) If a bryophyte’s carbon loss is greater than its carbon intake over an extended period the plant will die.

For the experiment, bryophytes growing at altitudes of 1,200 meters were transplanted in study plots at 500 meters. Bryophytes collected at an altitude of 500 meters were transplanted in study plots at sea level. The researchers then observed the transplanted plants for nearly two years to determine how the bryophytes responded in the short term and long term to the warmer temperatures and drier conditions of their new environments.

A majority of the bryophytes transplanted downhill to warmer spots died, but “the most striking result of our study was the finding that at least a few samples of most of the tested species survived higher temperatures for at least 20 months and totally recovered growth during this time,” botanists Sebastian Wagner, M.Y. Bader and Zotz write in a paper which appeared recently in the journal Plant Biology.

Research student Steve González takes growth measurements in a study plot of transplanted bryophytes at the Smithsonian Tropical Research Institute where scientists are assessing the ability of these plants to acclimate to global warming. (Photo by Sebastian Wagner)

“All species have a few individuals that can apparently deal with increased temperatures of 3 degrees Celsius,” Zotz says. “This indicates that there is indeed quite a bit of potential for acclimation.”

In light of these new findings, “it may be puzzling why we do not find more of these species in the lowlands,” Zotz points out. In fact, he continues, some highland bryophytes are found living in the warmer lowlands but they are usually restricted to moist microsites, such as the pendant mosses growing on Annona glabra trees around Lake Gatun, in Panama. Increased moisture may weaken the adverse impact of higher temperatures on bryophytes in the lowlands.

Bryophytes living in the lowlands in the tropics already seem to “live at the edge,” of their temperature tolerance,” Zotz adds. In an upcoming experiment “we are planning to expose lowland species to higher temperatures to see whether they are already at the very limit of their adaptive range,” Zotz says. “If this were true the predicted temperature increases in the future would have serious implications for lowland habitats.”

As the researchers conclude in their paper many species of bryophytes “from higher altitudes indeed will experience problems at higher temperatures,” with their population ranges potentially being shifted uphill.

Still, a second scenario for the impact of rising temperatures on bryophytes in the tropics is for “individuals having the acclimation potential to maintain populations at the present altitude, evolving to be better adapted to high temperatures,” the study says. Some species with a large acclimation potential might even benefit from global changes due to elevated carbon dioxide concentrations and/or reduced competition.  –John Barrat

The impact of industrial fishing on coastal ecosystems has been studied for many years. But how it affects food webs in the open ocean―a vast region that covers almost half of the Earth’s surface―has not been very clear. So a team of Smithsonian and Michigan State University scientists and their colleagues looked to the ancient bones of seabirds for answers, revealing some of the dramatic changes that have happened within open-ocean food webs since the onset of industrial fishing. The team’s research is published this week in the Proceedings of the National Academy of Sciences.

A Hawaiian petrel flies over part of its Pacific Ocean foraging grounds. (Photo by Jim Denny)

Few records of species that live in the open ocean date back more than 60 years, and the sheer size of open-ocean regions makes their food webs difficult to study. The Hawaiian petrel (Pterodroma sandwichensis), a crow-sized oceanic bird, offered the team a solution. These birds range widely over the northeast Pacific, and their diets integrate food webs from that vast area.

What the petrels have eaten is recorded in the chemistry of their bones. By extracting protein from bones and feathers and studying stable isotopes of carbon and nitrogen in the protein, the scientists were able to assess the birds’ diet and how it changed over centuries. What they found from bones 100 to 4,000 years old were nitrogen isotope ratios that were consistently high, indicating a diet of relatively large prey. Those less than a century old, after industrial fishing started, had low ratios, revealing a shift to smaller fish, squid and other prey.

“The question is, have the effects of open-ocean fishing gone beyond targeted species, like tuna,” said Anne Wiley, lead author, Smithsonian postdoctoral researcher and former MSU doctoral student. “Our study is among the very first to show that it has, and because Hawaiian petrels eat such a wide variety of prey over a large area, our results suggest that fishery influence may be widespread and profound in the Pacific. Understanding the influence of fisheries on open-ocean food webs has been one of the great mysteries of biological oceanography.”

In this image lead author Anne Wiley examines a newly discovered, ancient Hawaiian petrel skull from Puu Naio Cave, Maui. After radiocarbon dating, the team learned that this bird died around 1400 A.D. (Photo by Andreanna Welch)

The team’s isotope records are unusual because they are from all the known populations of the species, which breed on different Hawaiian Islands. The records show that separate populations of Hawaiian petrels hunted in different areas of the open ocean for thousands of years. The scientists revealed a foraging shift in multiple Hawaiian petrel populations, emphasizing that the petrels’ diets changed across a very broad expanse of the ocean. This sudden shift in the past 100 years suggests a relatively rapid change in the composition of oceanic food webs in the Northeast Pacific.

“Conservation efforts for endangered seabirds take place mainly on land at breeding colonies where there are obvious threats like introduced predators,” said Helen James, coauthor and research zoologist at Smithsonian’s National Museum of Natural History. “Our study suggests we should pay more attention to the lives of these birds at sea.”

What can you do to bring some of the Smithsonian’s 137 million objects to life? Put them in 3-D!

This is a full-time job for two of the Smithsonian’s very own “laser cowboys,” Vince Rossi and Adam Metallo, who work in the Smithsonian’s 3D Digitization Program Office. They work hard to document, in very high three-dimensional detail, many of the institution’s many priceless and important collections so that the objects are available for research, education and general interest.

Click here for Smithsonian 3-D Digitization on Facebook:

Covered in venomous spines the exotic and strikingly banded Indo-Pacific lionfish would be a painful mouthful to any creature that may try to catch and eat it. Brought into the United States by aquarium hobbyists untold years ago, scientists believe a few of these fish were discarded live into the Atlantic off southern Florida sometime around the late 1980s. Now this voracious species is found as far north as Virginia and south to Venezuela. They are spreading still.

At the Smithsonian’s Tropical Research Institute in Panama, Andrew Sellers is turning this invasion into opportunity by examining just what Atlantic parasites are adopting the lionfish as a host.

Andrew Sellers captures a large lionfish in Belize to take back to his laboratory for study.
(Photo by Edgardo Ochoa, dive officer at the Smithsonian Tropical Research Institute)

“Basically, I’m looking at how parasite abundance and diversity in the lionfish varies across latitudes,” Sellers explains.  “It has been suggested that invasive species don’t do as well in the tropics as they do in temperate areas, the theory being that stronger biotic interactions—competition for food, predators and parasitism—in the tropics may limit the success of an invasive species.

“As lionfish have spread so rapidly across such a broad lattudinal gradient, they make a very good model” says Sellers, who works in the Tropical Research Institute’s invasive species lab run by marine biologist Mark Torchin.

In addition to Panama, Sellers has traveled to Florida, Mexico and Belize catching lionfish and closely examining them to see what parasites are living on and inside their bodies. “For external parasites we’ve found—isopods and turbellaria, a flatworm that infects the gills. We have found that external parasites infecting the lionfish are more diverse at low latitudes,” he says.”

“Inside the fish we’ve found both trematodes [worms also known as flukes] and nematodes.”

Tropical Research Institute scientist Mark Torchin, left, and Andrew Sellers place a lionfish specimen in a special collecting bag which prevents the divers from being stung by the animals. This photo was taken in Belize.
(Photo by Edgardo Ochoa, Dive Officer at the Smithsonian Tropical Research Institute)

In his analysis Sellers examines and records the condition of each individual fish—size, weight, length—to see if the parasites are having any impact on their health.

“Overall, we are finding the abundance of parasites on the lionfish is pretty low, which is what we’d expect in an invasive species,” Sellers continues.

A lionfish in Bocas del Toro (Photo by Andrew Sellers)

Sellers also has begun looking into lionfish interactions with cleaner fish in the Caribbean. These small fish set up cleaning stations on brain coral heads where other fish—called client fish—congregate to have parasites removed from their bodies.

“What I am looking at is whether potential native competitors to lionfish are receiving a benefit from these cleaner fish that lionfish are not, i.e. parasite removal,” Sellers explains. “In general introduced species are believed to harbor fewer parasites than natives, however these cleaners may be affecting this imbalance by removing parasites from the native but not the invader.”

Female lionfish reproduce by laying a buoyant egg mass that is fertilized by a male, Sellers explains. The egg mass is then carried off into the ocean currents—a very effective method of dispersal. By 2005 people began seeing lionfish in the Bahamas. “We started seeing them in Panama about 2008, 2009,” Sellers says. “Now divers can find them everywhere along the coast from 0 to 300 feet down.” Cold water intolerance has limited their spread north along the coast of the United States to just below New York.

“Basically it appears the Atlantic coast of Central and South America is a pretty good place for these fish,” Sellers says. “It appears they have plenty of food, no enemies and few parasites.” –John Barrat

All bear species except for one live in either temperate or tropical woodlands. Only the polar bear is a stranger to the forest, living and foraging instead across vast expanses of barren polar ice. But don’t be deceived, its habitat is not thin and flat like a skating rink but a thick and complex mix of old multi-year ice, new seasonal ice and open water. Polar bears hunt seals in this environment and live and breed on top of their frozen habitat. Recently, warming temperatures have had an enormous impact on the domain of this remarkable mammal.

Here, bear expert Don Moore, associate director of Animal Care Sciences at the Smithsonian’s National Zoological Park, answers a few questions about polar bears, rising temperatures and the future for Smithsonianscience.org.

A polar bear on an ice floe in Wagner Bay, Canada (Photo by Ansgar Walk)

Q: How many polar bears are found in the wild today?

Moore: Polar scientists estimate there are 20,000 to 25,000 polar bears in the five polar bear countries—the United States/Alaska, Canada, Russia, Denmark/Greenland and Norway.

Q: How much ice does one polar bear require?

Moore: Polar bears range over hundreds and even thousands of miles. They come ashore only when their ice melts in summer, in the Western Hudson Bay for instance.

Q: Can you compare the amount of ice sheets in their ecosystem 10 years ago to now? 

Moore: Ten years ago the Arctic Ocean was land-fast with a lot of year-round ice. Recent summer ice losses have been enormous, and in 2012 summer ice losses in the Arctic were larger than the area of the United States. Since Arctic ice is the polar bear’s habitat, bear populations are declining as the ice declines.

Q: Has the polar bear population decreased significantly since you started to study them?

A polar bear on the Islands of Svalbard, the Netherlands. (Photo by Paul W.J. Groot)

Moore: More populations are declining now than before. For example, the Western Hudson Bay population in Churchill, Manitoba in Canada has declined by more than 20 percent in the last 30 years.

Q: When the polar bears’ habitat melts, how do they adapt? Do they use more land to migrate and hunt? What impact does that have on other land animals?

Moore: Polar bears whose habitat melts seasonally must move onto land. But it has been hundreds of thousands of years since polar bears evolved from brown bears. Polar bears are built for eating seals, and cannot live a healthy life for long periods of time eating rodents and plants that brown bears eat. Some have adapted by eating harbor seals or beluga whales, but this behavior will be short-term.

Q: How have changes in the polar bears’ habitat changed the way you conduct your research?

Moore: The Arctic is a forbidding place, and very dangerous to travel in during the 6 months of darkness when winter sets in. Most of my biologist friends take helicopters from land bases to the ice offshore where polar bears live in spring and fall. These times of year can be very stormy, and as the ice has melted it has gotten farther away from shore. Biologists take huge risks flying hundreds of miles by helicopter to the nearest ice. Many researchers have cancelled research trips in recent years so they don’t endanger their study teams.

Q: For most of us, the problems of the polar bear are remote and far away. How do our actions impact these animals hundreds of miles away?

Moore: To help slow climate change we need to change our behavior and put less carbon into the atmosphere. Carbon comes from factories, cars, and other polluting, man-made objects on the planet. If we reduce, recycle and reuse we can reduce the amount of gas going into the atmosphere. Every single person can make a difference and help conserve the planet’s resources.

–Emily Grebenstein

Striking Caribbean sunsets occur when particles in the air scatter incoming sunlight. But a particulate shadow over the sea may have effects underwater. A research team, including staff scientist Héctor Guzmán from the Smithsonian Tropical Research Institute, linked airborne particles caused by volcanic activity and air pollution to episodes of slow coral-reef growth.

Sunset over the Caribbean. A key driver of reduced growth rates at some Caribbean reef locations is regional climate change due to volcanic and human source aerosol emissions, a new study suggests.

Like tree rings, long-lived coral skeletons preserve a record of coral growth. Previously, scientists linked coral-growth patterns in the Caribbean to a phenomenon called the Atlantic Multi-decadal Oscillation—fluctuations in sea-surface temperatures and incoming sunlight.

In order to better predict the effects of climate change and human disturbance on reefs, Lester Kwiatkowski, University of Exeter, and researchers from the University of Queensland, the Australian Nuclear Science and Technology Organization and STRI analyzed coral-growth records from Belize and Panama spanning the period from 1880 to 2000. An Earth-system model simulation told them how well sea-surface temperature, short-wave radiation and aragonite-saturation state, a measure of ocean acidification, predicted changes in coral growth.

Their data came from several coral cores drilled in reefs near the Atlantic entrance of the Panama Canal formed by the coral species Siderastrea siderea between 1880 and 1989, whereas samples from the Turneffe atoll in Belize showed growth fluctuations in the coral species Montastrea faveolata from 1905 to 1998.

Particles from air pollution, primarily sulfate, reflect incoming sunlight and make clouds brighter reducing the amount of sunlight reaching the sea surface. Coral growth corresponded closely to sea surface temperatures and light levels. Growth fluctuations in the late 19th and early 20th centuries were largely driven by volcanic activity.

Researchers explain a dive in surface temperatures and coral growth in the 1960s by increased air pollution associated with post-World War II industrial expansion in North America and to a lesser extent in Central and South America.

The influence of human aerosol emissions was more pronounced in coral cores from Belize, perhaps because Belize is closer to sources of industrial emissions. Fluctuations unexplained by the model, especially in the growth records from Panama, probably result from runoff from deforestation and from the construction of the Panama Canal waterway.

“The coral growth chronology for Panama allowed us to identify the effects of human interventions at the beginning of 1900s,” said Guzmán, “but the decline in growth observed by the middle of the 20th century corresponding to the beginnings of the industrial era in coastal Panama remained unresolved by the model.”

“Our study suggests that coral ecosystems are likely to be sensitive to not only future global atmospheric carbon dioxide concentration but also to regional aerosol emissions associated with industrialization and decarbonization,” said Kwiatkowski.

A century from now researchers will gather data from a forest in Maryland to see how, during the previous 100 years, varying levels of species diversity affected its development and how the forest reacted to climate change. The information researchers garner could be critical for conservation, and they will have Smithsonian scientists who planted the entire forest back in 2013 to thank.

Scientists at the Smithsonian Environmental Research Center in Edgewater, Md., are turning 60 acres of farmland into an experimental forest and watching it grow for 100 years. With the help of volunteers, they planted 24,000 tree saplings of 16 species in fields once used to grow tobacco and corn. This was the initial step in a long-term research project called BiodiversiTree.

Smithsonian ecologist John Parker examines just a few of the 24,000 tree saplings that will one day turn this Maryland cornfield into a mature forest. During the next 100 years, Smithsonian scientists will examine how varying levels of species diversity affects the forest’s development and how it reacts to climate change. (John Gibbons photo)

The saplings are divided into 120 plots across the fields―some plots holding 12 species, others with only four or just a single species. The main goals are to see if a forest with high diversity, versus low, is healthier; how species respond to a changing climate; and whether a native forest is better than agricultural lands at filtering out nutrients and pollutants in a watershed of the Chesapeake Bay.

“Species are going extinct faster than they ever have before, the climate is rapidly changing, and yet humans still depend on forests and other ecosystems for basic goods and services,” said John Parker, ecologist at SERC and lead scientist for BiodiversiTree. “It’s critical for future generations that we understand the implications of these changes.”

While the project is designed to last more than a century, researchers will not have to wait that long to start seeing results. Within the next few years scientists will begin tracking how different combinations of species grow, die, bury carbon, absorb nutrients, resist enemies and drought and enhance forest diversity overall. This will begin to shed light on how a diverse forest functions relative to a species-poor forest.

An underlying challenge for all the saplings, regardless of their plot and species combination, is the ground they are planted in.
“The fields we are planting have been in continuous corn for more than 30 years,” said Whitney Hoot, project coordinator for BiodiversiTree. “Without crop rotation or other best-management practices, a continuous corn monoculture depletes the soil of nutrients, and results in reduced topsoil. As these trees grow, we will be able to analyze the changing soil quality and observe the impacts that a secondary forest can have on the restoration of degraded farmland. We have a great opportunity to restore the quality and fertility of the depleted soil.”

While the soil may not be ideal, the study’s location is. It is a significant watershed to the Chesapeake Bay and allows scientists to examine one of the growing forest’s main functions as a water filter. The root systems of a forest keep soil porous and allow water to filter through various layers. This helps remove toxins, nutrients and sediment before the water enters streams, rivers and in this case, the Chesapeake Bay.

Crops like corn, which grew on the site before, require a lot of fertilizer to foster growth. Now the scientists will continually test the water quality in the main stream linking the site to the bay and see if it changes as the young forest and its root system grow over time.

Once the last remaining saplings are planted next week, the team will put small cages around each sapling to protect them from deer, start sampling the soil and the plants to assess baseline conditions, and do it all again in about three years from now to try and answer a fundamental question in these changing times: Does diversity matter?

Flowers of the Goodyera pubescens orchid (downy rattlesnake plantain). (Photo by Melissa McCormick/SERC)

Invasive European earthworms could prevent roughly half a North American forest’s orchid seeds from even germinating, ecologists from Smithsonian Environmental Research Center and Johns Hopkins University discovered in a new study published online in Annals of Botany Plants.

The small size of orchid seeds (they are barely the size of dust grains) makes them particularly vulnerable. As earthworms chew up forest litter, they ingest orchid seeds as well. When that happens, two things can keep the seeds from germinating: One, the process of passing through an earthworm’s gut can render them unviable. Or two, if the seeds survive ingestion, they can end up buried so deep that they can’t access the fungi they need to germinate and grow. As a general rule, deeper soils are much less likely to have those fungi.

Learn more at Shorelines, the blog of the Smithsonian Environmental Research Center.

Among vertebrates few animals rival poison dart frogs for their vibrant electric blue, yellow, red and orange skin colors. Some experts have long believed these pigments serve as a visual warning for hungry birds, snakes and other animals to steer clear from the frog’s deadly skin toxins. Now, new research by Paul Weldon, a chemical ecologist at the Smithsonian Conservation Biology Institute, has thrown this long-standing assumption into doubt. In a recent study Weldon and his colleagues have discovered a number of poisonous alkaloids (naturally occurring chemical compounds) on the skin of dendrobatid (poison dart) frogs that are better suited for defense against ants and other biting forest arthropods, than vertebrates.

Paul Weldon

Here Weldon answers a few questions about the study, recently published in the journal Naturwissenschaften, for Smithsonianscience.org.

Q. How many alkaloids do poison dart frogs have on their skin and how many have you tested?

Weldon: Some 500 alkaloids representing 20 different structural classes of chemicals have been identified on the skin of these frogs. We’ve tested 20 and in the process stumbled on some so potent to ants, that, in my view, it is clear they are designed to defend against arthropods, not vertebrates.

Think about it, frogs probably encounter a couple of vertebrates every few days but they come into contact with ants and millipedes and many other potentially offending arthropods all the time. What we’ve shown in this paper is that the consumers these frogs typically encounter are stopped quite effectively by a few of these alkaloids.

Q. Certainly others have studied these compounds before you?

Weldon: Yes. Few vertebrates have been studied as intensely as the dendrobatid frogs for their chemical defenses. Yet no one, and I mean literally no one, has focused on arthropods as the offenders of these frogs. People have entered into the study with the foregone conclusion that their alkaloid toxins work against vertebrates.

Blue Poison Dart Frog, Dendrobates azureus. (Photo by Jessie Cohen)

It turns out that some of these compounds clearly seem customized to go through the cuticle (thick waxy coating) of an ant, which in and of itself is a task, and to target the neurochemistry of the ant once inside. An ant is covered with wax, the cuticle is really a chitin, a polymeric sugar, a polysaccharide that it has all over it, a waxy covering that prevents the loss of water. So any compound that goes through the cuticle has to go through a layer of wax and then has to go through a layer of polymeric sugar. There aren’t too many compounds with properties that allow them to penetrate those two kinds of layers.

Q. Do the frogs create the toxic alkaloids found on their skin?

Weldon: No, the frogs ingest ants, millipedes, mites and other leaf-litter arthropods that have these compounds naturally occurring in their skin. These smaller creatures biosynthesize the toxic compounds from things they eat on the forest floor, such as decaying plant material. The frogs eat them and the compounds are then transferred into the frog’s skin glands where they are stored and secreted.

Head view of a red imported fire ant, Solenopsis invicta, showing its cuticle or waxy coating . Source AntWeb.org

Frog skin chemistry ultimately reflects to one degree or another, what particular prey they have taken. You can find geographic variation in the skin chemicals of these frogs based upon what the available arthropods are in the different locales. Poison dart frogs raised in captivity and fed upon fruit flies don’t have skin chemicals that protect them.

Q. How do the toxins get from the frogs’ stomachs to their skin?

Weldon: We know very little about how these frogs transfer alkaloids from their food to their skin glands. It probably goes through the intestinal lining or it might have something to do with bile acids facilitating the transport of the compounds into the body—but that is pure speculation. Apparently they can get a lifetime supply of skin compounds from just one afternoon’s feeding of ants.

Q: Where do you get these compounds for your experiments?

The Ecuadorian poison dart frog, Epipedobates anthonyi

Weldon: From the National Institutes of Health. Years ago NIH scientist John Daly traveled to the tropics and isolated these compounds from the skin of dendrobatid frogs. While we know what the compounds are, we need more accurate information on their abundances and concentrations on the frogs’ skin.

We tested the ambulatory responses of individual fire ants after contact with a very small amount of the dried residue of these alkaloids. Thirteen compounds had contact toxicities, seven had none. We tested the compounds in a very fine-tuned way by serially diluting the solutions and showing that some of them work in very, very vanishingly small concentrations. The dilutions of some of the compounds went down amazingly low, representing a huge amount of work. This paper was about six years in the making.

Q. Seven of the compounds had no toxicity?

Weldon: That is correct. To call all of these compounds ‘toxins’ is misleading. Nontoxic skin compounds may have other uses such as making the frogs taste bad or they may be antibiotic in their mode of action. They also could just be something the ants ingested and that appears on their skin.

There are so many compounds on the skin of these frogs that I think one must actually enter into the study of them expecting beforehand that different organisms will be affected by different compounds. And we’ve just shown from our very brief survey of 20 compounds that a few act very well as anti-arthropod toxins.

Q. One might assume that your interest in these compounds is in developing some type of insecticide?

Weldon: When you say insecticides that implies potential industrial use, it implies technology transfer, and it implies maybe even patents. I don’t get involved in any of that. I’ve been very fortunate because people, who I’ve identified as collaborators at the U.S. Department of Agriculture, support my work. But it’s not with the standard expectation that this discovery will ultimately end up in a patentable product. I particularly argue against that. I can’t do work with any animal extracts if that is the understanding.