June 14, 2013
In the past two decades, we’ve seen dramatic images of ice shelves and the floating tongues of glaciers crumble into the ocean. The summer of 2012 saw a huge chunk of ice–two times the size of Manhattan–snap off of Greenland’s Petermann Glacier. Two years earlier, a piece of ice twice as big as that one split from the glacier’s front. In early 2002, ice covering an area the greater than the size of Rhode Island sloughed into the ocean from a lobe of the Antarctic Peninsula’s Larsen Ice Shelf, releasing into the ocean three-quarters of a trillion tons of ice. Seven years before that, the northernmost sector of the same ice sheet completely collapsed and an area of ice roughly the size of Hawaii’s Oahu island dissolved into the sea.
Scientists have long thought that sudden and dramatic ice calving events like these, along with more moderate episodes of calving that occur daily, were the main mechanisms for how polar ice gets lost to the sea. New research, however, shows that calving icebergs is only the tip of the iceberg–seawater bathing the undersides of ice shelves contributes most to ice loss even before calving begins, at least in Antarctica.
The discovery, published in the journal Science, shows that interactions with the ocean underneath floating ice account for 55 percent ice lost from Antarctic ice shelves between 2003 and 2008. The researchers arrived at their findings by studying airborne measurements of ice thicknesses from radar sounders and the rates of change in ice thickness based off of satellite data. Combining these data allowed them to calculate the rates of bottom melting.
Given that thick platforms of floating ice surround nearly 75 percent of Earth’s southernmost continent, covering nearly 580 million square miles, ice melted in this fashion may well be the main contributor to sea level rise. “This has profound implications for our understanding of interactions between Antarctica and climate change.” said lead author Eric Rignot a researcher at UC Irvine and NASA’s Jet Propulsion Laboratory, in a statement. “It basically puts the Southern Ocean up front as the most significant control on the evolution of the polar ice sheet.”
Interestingly, the big ice shelves–Ross, Ronne and Filchner, which cover about 61 of Antarctica’s total ice shelf area–only contribute a small fraction meltwater through their bases. Instead, less than a dozen small ice shelves, particularly those on the Antarctic Peninsula, are responsible for most–nearly 85 percent–of the basal melting observed by the authors during their study period. These shelves not only float in warmer water, relatively, but their small sizes may mean that their interiors are less sheltered from already warmer ocean waters that creep underneath the ice.
The findings reveal a lot about the vulnerability of polar ice in a warming world. Ice sheets ooze through glaciers to the sea, where they interlace and form ice shelves. These shelves are akin to a cork that keeps the contents inside from spewing out–when ice sheets collapse, the glaciers that feed them thin and accelerate, helping to drain the interior ice sheet. Polar ice sheets already are losing at least three times as much ice each year as they were in the 1990s, and the findings released today may give a mechanism for this frantic pace.
In fact, the major ice calving events of the last two decades on the Petermann Glacier and Larsen Ice Shelf may have started with the fact that melting from underneath was weakening the ability of ice to coalesce into a solid mass.
“Ice shelf melt can be compensated by ice flow from the continent,” Rignot added. “But in a number of places around Antarctica, they are melting too fast, and as a consequence, glaciers and the entire continent are changing.”
June 7, 2013
Ocean plants produce some 50% of the planet’s oxygen. Seawater absorbs a quarter of the carbon dioxide we pump into the atmosphere. Ocean currents distribute heat around the globe, regulating weather patterns and climate. And, for those who take pleasure in life’s simple rewards, a seaweed extract keeps your peanut butter and ice cream at the right consistency!
Nonetheless, those of us who can’t see the ocean from our window still feel a disconnect—because the ocean feels far away, it’s easy to forget the critical role the ocean plays in human life and to think that problems concerning the ocean will only harm those people that fish or make their living directly from the sea. But this isn’t true: the sea is far more important than that.
Every year, scientists learn more about the top threats to the ocean and what we can do to counter them. So for tomorrow’s World Oceans Day, here’s a run-down of what we’ve learned just in the past 12 months.
This year, we got the news that the apparent “slow down” in global warming may just be the ocean shouldering the load by absorbing more heat than usual. But this is no cause to celebrate: the extra heat may be out of sight, but it shouldn’t be out of mind. Ocean surface temperatures have been rising incrementally since the early 20th century, and the past three decades have been warmer than we’ve ever observed before. In fact, waters off the U.S. East Coast were hotter in 2012 than the past 150 years. This increase is already affecting wildlife. For example, fish are shifting their ranges globally to stay in the cooler water they prefer, altering ecosystems and fisheries’ harvests.
Coral reefs are highly susceptible to warming: warm water (and other environmental changes) drives away the symbiotic algae that live inside coral animals and provide them food. This process, called bleaching, can kill corals outright by causing them to starve to death, or make it more likely that they will succumb to disease. A study out this year found that even if we reduce our emissions and stop warming the planet beyond 2°C, the number considered to be safe for most ecosystems, around 70% of corals will degrade and die by 2030.
Although coral reefs can be quite resilient and can survive unimaginable disturbances, we need to get moving on reducing carbon dioxide emissions and creating protected areas where other stressors such as environmental pollutants are reduced.
More than a hit of acid
The ocean doesn’t just absorb heat from the atmosphere: it also absorbs carbon dioxide directly, which breaks down into carbonic acid and makes seawater more acidic. Since preindustrial times, the ocean has become 30% more acidic and scientists are just starting to unravel the diverse responses ecosystems and organisms have to acidification.
And it really is a variety: some organisms (the “winners”) may not be harmed by acidification at all. Sea urchin larvae, for instance, develop just fine, despite having calcium carbonate skeletons that are susceptible to dissolving. Sponges that drill into shells and corals show an ability to drill faster in acidic seawater, but to the detriment of the organisms they’re boring into.
Nonetheless, there will be plenty of losers. This year saw the first physical evidence of acidification in the wild: the shells of swimming snails called pteropods showed signs of dissolution in Antarctica. Researchers previously found that oyster larvae fail under acidic conditions, potentially explaining recent oyster hatchery collapses and smaller oysters. Acidification may also harm other fisheries.
Plastic, plastic, everywhere
Americans produced 31 million tons of plastic trash in 2010, and only eight percent of that was recycled. Where does the remaining plastic go? A lot of it ends up in the ocean.
Since last World Oceans Day, trash has reached the deep-sea and the remote Southern Ocean, two of the most pristine areas on Earth. Most of the plastic trash in the ocean is small—a few centimeters or less—and can easily be consumed by animals, with damaging consequences. Some animals get hit on two fronts: when already dangerous plastic degrades in their stomachs it leaches toxic chemicals into their systems. Laysan albatross chicks are fed the bits of plastic by their parents in lieu of their typical diet and one-third of fish in the English Channel have nibbled on plastic.
Where have all the fish gone?
A perennial problem for the ocean, overfishing has only gotten worse with the advent of highly advanced gear. Despite fishing fleets going farther and deeper, the fishing gains are not keeping up with the increased effort.
Our brains can’t keep up either: even as we catch fewer fish, we acclimate to the new normal, adjust to the shifting baseline, and forget the boon that used to be, despite the fact that our memories are long enough to realize that most of the world’s fisheries (especially the small ones that aren’t regulated) are in decline.
Thankfully, those responsible for managing our fisheries are aware of what’s at stake. New knowledge about fish populations and their role in ecosystems can lead to recovery. A report from March 2013 shows that two-thirds of U.S. fish species that are closely managed due to their earlier declines are now considered rebuilt, or on their way.
Learn more about the ocean from the Smithsonian’s Ocean Portal. This post was co-authored by Emily Frost and Hannah Waters.
June 3, 2013
In recent weeks, photos of lobsters have been floating around social media with captions calling the crustaceans “biologically immortal.” Anyone with an Internet connection can even create a meme juxtaposing this fact with a joke of his or her own. But is this fun fact actually, well, fact?
The viral scientific tidbit can be traced back to a brief 2007 news story that reports that lobsters don’t show typical signs of a phenomenon known as senescence. In plain terms, the report says that lobsters don’t age the way other living creatures do—they don’t lower their reproductive ability, slow their metabolism or decrease in strength. This led to extrapolations that lobsters, if left undisturbed, can’t die. Other websites write that lobsters’ incredible longevity is courtesy of their DNA, with credit specifically due to telomerase, an enzyme used in cell division that protects the ends of chromosomes.
The popular graphic and its different textual iterations caught the eye of Zen Faulkes, an invertebrate neuroethologist at the University of Texas-Pan American, who sussed out the situation on his blog and came to this conclusion: “If there is evidence supporting that claim,” he wrote in an email, “I have not found it yet.”
It’s true that lobsters continue eating, reproducing and growing until the end. And there is an end—they’re not immortal. But like most decapod crustaceans, which also include crayfish and shrimp, they have indeterminate growth. That means they don’t reach a set size limit in their lifetimes, continuing to grow until they die of natural causes or are killed.
Lobsters grow by molting their hard exoskeleton, and they do so a lot: the average lobster can molt 44 times before it’s a year old. By the time lobsters reach the age of seven, they molt once a year, and after that, once every two to three years, growing larger with each successive shedding of its exoskeleton. The largest lobster on record, caught in Nova Scotia in 1977, weighed 44 pounds, six ounces and measured 3.5 feet in length. Last year, fishermen caught a 27-pound lobster, roughly the size of a toddler–the largest in Maine’s history. For lobsters, bigger bodies translate into more reproductive success: females can carry more eggs as their body volume increases, and they keep producing them until they die.
Molting is a stressful process. Losing an exoskeleton leaves the critter, now without a hard shell and strong pincers, temporarily vulnerable to predators. But predation isn’t senescence. So what would be a natural death for lobsters?
According to Carl Wilson, lead lobster biologist with the Maine Department of Marine Resources, between 10 and 15 percent of lobsters die naturally each year as they shed their exoskeletons because the exertion proves to be too much. Each molting process requires more and more energy than the one before it as lobsters grow in size.
Finally, older crustaceans stop shedding their exoskeletons altogether—a clue that they’re near the end of their lifespans. They run out of metabolic energy to molt, and their worn-and-torn shells contract bacterial infections that weaken them. Shell disease, in which bacteria seeps into lobster shells and forms scar tissue, adheres the crustaceans’ bodies to their shells. The lobster, attempting to molt, gets stuck and dies. The disease also makes lobsters susceptible to other ailments, and in extreme cases, the entire shell can rot, killing the animal inside.
“Is that senescence? Maybe not in how we think about it,” says Jeffrey D. Shields, a marine science professor in the Virginia Institute of Marine Science of the College of William & Mary. “But it is senescence in the way that older people die of pneumonia.”
But one question about lobsters’ lifespans still remains. Scientists do not yet have a truly validated way of determining the age of lobsters. “The problem with lobsters is when they molt, they molt their entire exoskeleton, including their digestive tract and gastric mill and the like, so there are no hard parts that are left,” Wilson says. These hard parts, if a trace of them were left after every molt, would help determine a creature’s age—without them, approximating lobsters’ birth years is difficult.
Previous research has suggested that the biggest European lobster males in the wild live an average of 31 years, and the females an average of 54 years. The work is based off assumed accumulation rates of fat residues found in the creature’s eyestalk. Other scientists are approximating the age of lobsters by measuring a pigment called neurolipofuscin that builds up in the crustaceans’ brains over time. Still more are studying discarded exoskeletons and counting growth bands deposited in the calcified body structures (PDF) to determine an average rate of growth for a given lobster, allowing scientists to estimate its age.
Scientists, however, are not looking for the secret of lobster immortality—it doesn’t exist.
May 17, 2013
Our oceans are taking a beating from overfishing, pollution, acidification and warming, putting at risk the many creatures who make their home in seawater. But when most people think of struggling ocean species, the first animals that come to mind are probably whales, seals or sea turtles.
Sure, many of these large (and adorable) animals play an important part in the marine ecosystem and are threatened with extinction due to human activities, but in fact, of the 94 marine species listed under the Endangered Species Act (ESA), only 45 are marine mammals and sea turtles. As such, these don’t paint the whole picture of what happens under the sea. What about the remaining 49 that form a myriad of other important parts of the underwater web?
These less charismatic members of the list include corals, sea birds, mollusks and, of course, fish. They fall under two categories: endangered or threatened. According to NOAA’s National Marine Fisheries Service (pdf), one of the groups responsible for implementing the ESA, a species is considered endangered if it faces imminent extinction, and and a species is considered threatened if it is likely to become endangered in the future. A cross section of these less-known members of the ESA’s list are described in detail below.
1. Staghorn coral (Acropora cervicornis), pictured above, is one of two species of coral listed as threatened under the ESA, although both are under review for reclassification to endangered. A very important reef-building coral in the Caribbean and the Gulf of Mexico, it primarily reproduces through asexual fragmentation. This means that its branches break off and reattach to a substrate on the ocean bottom where they grow into new colonies.
While this is a great recovery method when only part of a colony is damaged, it doesn’t work so well when most or all of the colony is killed—which often is the result from disturbances afflicting these corals. Since the 1980s, staghorn coral populations have steeply declined due to outbreaks of coral disease, increased sedimentation, bleaching and damage from hurricanes. Although only two coral species are currently on the ESA list, 66 additional coral species have been proposed for listing and are currently under review.
2. The white abalone (Haliotis sorenseni), a large sea snail that can grow to ten inches long, was the first marine invertebrate to be listed under the ESA but its population hasn’t recovered. The commercial fishery for white abalone collapsed three decades ago because, being spawners that jet their eggs and sperm into the water for fertilization with the hope that the two will collide, the animals depend on a large enough population of males and females being in close proximity to one another to reproduce successfully.
Less than 0.1% of its pre-fished population survives today, and research published in 2012 showed that it has continued to decline since its ESA listing more than a decade ago. The researchers recommended human intervention, and aquaculture efforts have begun in an effort to save the species.
3. Johnson’s seagrass (Halophila johnsonii), the lone marine plant species listed, is classified as threatened and makes coastal habitats and nurseries for fish and provides a food source for the also-endangered West Indian manatees and green sea turtles. However, its most important role may be long-term ocean carbon storage, known as blue carbon: seagrass beds can store more carbon than the world’s forests per hectare.
The main threats to Johnson’s seagrass are nutrient and sediment pollution, and damage from boating, dredging and storms. Its plight is aggravated by its tiny geographic range–it is only found on the southeast coast of Florida. The species may have more trouble recovering than other seagrass species because it seems to only reproduce asexually–while other seagrasses can reproduce like land plants, by producing a flower that is then fertilized by clumps of pollen released underwater, the Johnson’s seagrass relies on the sometimes slow process of new stems sprouting from the buried root systems of individual plants.
4. The short-tailed albatross (Phoebastria albatrus) differs from some of its neighbors on the ESA list in that an extra layer of uncertainty is added to the mix: During breeding season, they nest on islands near Japan, but after breeding season ends, they spread their wings and fly to the U.S. In the late 19th century, the beautiful birds are thought to have been fairly common from coastal California up through Alaska. But in the 1940s, their population dropped from the tens of millions to such a small number that they were thought to be extinct. Their incredible decline was due to hunters collecting their feathers, compounded by volcanic damage to their breeding islands in the 1930s.
Today they are doing better, with over 2,000 birds counted in 2008, but only a few islands remain as nesting sites and they continue to be caught as bycatch, meaning that they are often mistakenly hooked by longline fishing gear.
5. Salmon are a familiar fish frequently seen on the menu. But not all species are doing well enough to be served on our plates. Salmon split their time between freshwater (where they are born and later spawn) and the ocean (where they spend their time in between). Historically, Atlantic salmon in the U.S. were found in most major rivers on the Atlantic coast north of the Hudson, which flows through New York State. But damming, pollution and overfishing have pushed the species to a point where they are now only found along a small section of the Maine coast. Twenty-eight populations of Pacific salmon are also listed as threatened or endangered. Efforts on both coasts are underway to rebuild populations through habitat restoration, pollution reduction and aquaculture.
The five organisms listed here are just a few of the marine species on the ESA’s list. In fact, scientists expect that as they learn more about the oceans, they will reveal threats to more critters and plants.
“The charismatic marine species, like large whales [and] sea turtles…were the first to captivate us and pique our curiosity to look under the waves,” says Jonathan Shannon, from the NOAA Fisheries Office of Protected
Species Resources. “While we are learning more about the ocean and how it works every day, we still have much to learn about the different species in the ocean and the health of their populations.”
Learn more about the ocean from the Smithsonian’s Ocean Portal.
May 9, 2013
With their big, glossy black eyes and downy fluff, baby Weddell seal pups are some of the most adorable newborns in the animal kingdom. But these cute infants are far from helpless bundles of joy. New research published in the journal Marine Mammal Science reveals that Weddell seal pups likely possess the most adult-like brain of any mammal at birth.
The seal pups’ brains, compared to adult seals’ brain proportions, are the largest known for any mammal to date. The researchers write that this is “remarkable” considering that the pups are quite small at birth compared to many other newborn mammals.
To arrive at these findings, a team of researchers from the Smithsonian Environmental Research Center and the National Museum of Natural History traveled to Antarctica to collect fresh pups specimens. They took advantage of the fact that many pups never make it to adulthood due to stillbirths, abandonment and accidental death, such as being crushed by an adult. The researchers collected 10 dead seal pups (which quickly freeze in the Antarctic temperatures), conducted a few measurements and then decapitated and shipped the frozen heads back to the Smithsonian. They also tossed in a couple adult Weddell seal heads into the mix, one of which had died from acute toxemia–possibly from its gut being punctured by a fish spine–and the other whose cause of death could not be determined.
Back in the U.S., the researchers partially thawed the skulls in a lab and–like a well picked-over Thanksgiving turkey–manually peeled the tissue off of the baby seal faces. Then, they drilled into the skulls to extract the intact brains. Finally, they put the bones into a tank full of flesh-eating beetles to remove any remaining scraps of meat. Clean skulls and brains in hand, they went about taking measurements, and they also drew upon measurements of some older Weddell Seal skull specimens from the museum’s collection.
Remarkably, baby Weddell seal brains are already 70 percent developed at birth, the team found. Compare this to human infants, whose brains are a mere 25 percent of their eventual adult mass. As a Smithsonian statement explains, baby animals born with proportionally larger brains usually live in challenging environments in which they need to act quickly in order to survive. Other animals that share this trait include most marine mammals, zebras and wildebeest.
For Weddell seal pups, large brains likely help with diving under ice sheets and orienting themselves under water at less than three weeks old–an extremely dangerous task for any mammal, newborn or not. The pups must acclimate quickly since Weddell seal mothers abandon their young at about 6 weeks old, meaning they need to be able to completely fend for themselves when that day arrives.
In nature, however, everything comes with a price. The Weddell seal pups may have the biggest, best developed brains on the block when compared to what they will be as adults, but this metabolically taxing organ requires excessive energy to maintain. A pup weighing just 65 pounds needs between 30 to 50 grams of glucose per day in order to survive, and the team estimates that the energetically hungry brain may account for a full 28 grams of that demand.
Luckily for the seal pups, their mothers’ milk is almost exactly matched to the babies’ caloric needs. Weddell seal milk supplies about 39 grams of sugar per day. Females seals, however, lose significant weight while tending to their young, which jeopardizes their own survival. At their mother’s cost, the babies’ brains are allowed to thrive. That is, until their mother decides she’s had enough with the nurturing and leaves her pups to survive on their own.