Staghorn coral is listed as threatened under the U.S. Endangered Species Act. NOAA Fisheries has proposed it be reclassified as endangered. Photo by Albert Kok

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.

The white abalone population off the coast of California continued to decline even after the closure of its short-lived fishery in the 1970s. Photo by John Butler, NOAA

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.

Johnson’s seagrass is the first, and only, marine plant listed under the Endangered Species Act. Photo by Lori Morris, St. Johns River Water Management District

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.

Short-tailed albatrosses have made a remarkable recovery since they were believed to be extinct in the 1940s. They still face threats today though, from habitat loss to being caught unintentionally by fishing gear. Photo by U.S. Fish and Wildlife Service

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.

Atlantic salmon used to be found in most major rivers in New England, now they are only found in a small section of Maine. Photo by E. Peter Steenstra/USFWS

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. “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. 

Helpless babe or capable professional navigator? Photo by Samuel Blanc

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.   

How many unborn brothers and sisters did this sand tiger shark devour to be here today? Photo by Amada44

Baby animals may seem irresistibly adorable, but in reality many of them are calculating killers. Hyena, wolf or even dog litter runts are pushed aside by their larger siblings and left to go hungry; fuzzy white egret chicks will kick their weaker clutch mates out of the nest to certain doom; and  baby golden eagles sometimes go so far as to snack on their smaller brothers and sisters while their mother looks on.

Perhaps most disturbing of all, however, is the case of the baby sand tiger shark. While sharks may not be the most snuggly animals to begin with, the sand tiger shark sets a new precedent for fratricide. This species practices a form of sibling-killing called intrauterine cannibalization. Yes, “intrauterine” refers to embryos in the uterus. Sand tiger sharks eat their brothers and sisters while still in the womb.

Even by nature’s cruel standards, scientists admit that this is an unusual mode of survival. When sand tiger sharks develop in their mother’s uteri (females have both a left and right uterus), some–usually the embryo that hatched first from its encapsulated, fertilized egg–inevitably grow faster and larger than others. Once the largest embryos cross a certain size threshold, the hungry babies turn to their smaller siblings as convenient meals. “The approximately 100 mm hatchling proceeds to attack, kill and eventually consume all of its younger siblings, achieving exponential growth over this period,” a team of researchers who investigated the phenomenon wrote this week in Biology Letters.  

Size differential between a recent hatchling (H) and an older embryo (E) from the same uterus in a typical litter the researchers samples. Photo by Chapman et al., Biology Letters

From what began as two uteri full of a dozen embryos results in just two dominating baby sand tiger sharks coming full term. What’s more, once the unborn babies consume all of the living embryos, they turn to their mother’s unfertilized eggs next, in a phenomenon called oophagy, or egg-eating. By the time those two surviving babies are finally ready to be introduced into the big, bright world, all of the pre-birth inner feasting has paid off. They emerge from their mother measuring in at about 95 to 125 centimeters long, or a bit longer than a baseball bat, meaning fewer predators can pick them off than if they had shared food with siblings and were smaller.   

This peculiar situation has implications for the genetic makeup of the species. Female sand tiger sharks, like many animals, mate with multiple males. Oftentimes in nature, females determine which males will sire the next generation by selectively choosing to mate with the most impressive bachelor (or bachelors) around. If mating with multiple males at any given time–as sharks, insects, dogs, cats and many other animals sometimes do–the babies that the female eventually produces share the same womb with siblings that may have different fathers. 

In this case, however, there are two modes of selection at work. Females may choose mates, but that does not guarantee those males’ genes will make the cut. The embryos the males sire will also have to survive the subsequent frenzy of cannibalism going on inside the female’s body. 

To find out whether some males are mating but missing out on actually producing offspring, the authors of this new study undertook microsatellite DNA profiling of 15 sand tiger shark mothers and their offspring. The researchers collected the sharks from accidental mortality events near protected beaches in South Africa between 2007 to 2012. By comparing the embryo genetics, the researchers could determine how many fathers were involved in fertilizing the eggs.

Nine of the females, or 60 percent, had mated with more than one male, the researchers found. When it came to which embryos hatched and grew large first (and thus would have survived if their mothers hadn’t have been killed), 60 percent shared the same father. This means that even if a female mates with more than one male, there is no guarantee that the male has been successful in passing on his genes. Rather, he could have just provided a convenient entree for another male’s offspring.

This also explains some male sand tiger shark behavior and physiology. Male sand tiger sharks often guard their mates against other males just after copulation. Males of this species also produce a conspicuously large amount of sperm compared to other sharks. Both of these characteristics increase the likelihood that the embryo fertilized by that male will successfully implant in the female’s uterus earlier, giving it a significant head start for developing more quickly than its siblings, which makes it more likely that the recent mate’s offspring will eat the others that may come along.

As for the females sand tiger sharks, some researchers think they actually may not have much of a choice when it comes to mating with multiple males.  It could be that females just give in to some amorous partners because the energetic cost of resisting those advances outweighs the cost of just conceding to the act–a behavior biologists call the convenience polyandry hypothesis. In this case, however, females may still get the final laugh since the males they first mated with and most likely preferred will have the greater chance of actually triumphing as the father of their children. “[Embryonic cannibalism] may allow female sand tigers to engage in convenience polyandry after mating with preferred males without actually investing in embryos from these superfluous copulations,” the researchers speculate.

While the females did invest in initially developing those doomed embryos, those investments are much smaller than what would be required to bring multiple embryos to full term. Those smaller embryos also represent resources allocated to the stronger, dominate embryonic winners, which thus have a better chance of surviving and passing on their mother’s genes than if she had spent the energy to instead birth multiple, weakling babies. In a way, the mother shark is providing nourishment for her strongest babies by producing multiple embryos that the most robust can eat. 

“This system highlights that competition and sexual selection can still occur after fertilization,” the authors write. For example, the first embryo to implant may not end up being the the one that survives the gladiator arena of the sharks uterus. While this new research still needs to delve into the details of the competition that takes place within the uterus, a picture is emerging based upon these initial findings: Females may chose which males to mate with or may be coerced into reluctantly mating, but male sperm fitness and the quality of the embryos they produce could also carry significant weight in which animals ultimately wind up as winners in this system. 

“This competition can play an important and probably under-appreciated role in determining male fitness,” the authors conclude. 

Emperor penguins swimming. Photo by Polar Cruises

Penguins seem a bit out of place on land, with their stand-out black jackets and clumsy waddling. But once you see their grace in the water, you know that’s where they’re meant to be–they are well-adapted to life in the ocean.

April 25 of each year is World Penguin Day, and to celebrate here are 14 facts about these charismatic seabirds.

1. Depending on which scientist you ask, there are 17–20 species of penguins alive today, all of which live in the southern half of the globe. The most northerly penguins are Galapagos penguins (Spheniscus mendiculus), which occasionally poke their heads north of the equator.

2. While they can’t fly through the air with their flippers, many penguin species take to the air when they leap from the water onto the ice. Just before taking flight, they release air bubbles from their feathers. This cuts the drag on their bodies, allowing them to double or triple their swimming speed quickly and launch into the air.

3. Most penguins swim underwater at around four to seven miles per hour (mph), but the fastest penguin—the gentoo (Pygoscelis papua)—can reach top speeds of 22 mph!

Gentoo penguins “porpoise” by jumping out of the water. They can move faster through air than water, so will often porpoise to escape from a predator. Photo: Gilad Rom (Flickr)

4. Penguins don’t wear tuxedos to make a fashion statement: it helps them be camouflaged while swimming. From above, their black backs blend into the dark ocean water and, from below, their white bellies match the bright surface lit by sunlight. This helps them avoid predators, such as leopard seals, and hunt for fish unseen.

5. The earliest known penguin fossil was found in 61.6 million-year old Antarctic rock, about 4-5 million years after the mass extinction that killed the dinosaurs. Waimanu manneringi stood upright and waddled like modern day penguins, but was likely more awkward in the water. Some fossil penguins were much larger than any penguin living today, reaching 4.5 feet tall!

6. Like other birds, penguins don’t have teeth. Instead, they have backward-facing fleshy spines that line the inside of their mouths. These help them guide their fishy meals down their throat.

An endangered African penguin brays with its mouth open, showing off the bristly inside of its mouth. Photo by Dimi P (Flickr), with permission

7. Penguins are carnivores: they feed on fish, squid, crabs, krill and other seafood they catch while swimming. During the summer, an active, medium-sized penguin will eat about 2 pounds of food each day, but in the winter they’ll eat just a third of that.

8. Eating so much seafood means drinking a lot of saltwater, but penguins have a way to remove it. The supraorbital gland, located just above their eye, filters salt from their bloodstream, which is then excreted through the bill—or by sneezing! But this doesn’t mean they chug seawater to quench their thirst: penguins drink meltwater from pools and streams and eat snow for their hydration fix.

9. Another adaptive gland—the oil (also called preen) gland—produces waterproofing oil. Penguins spread this across their feathers to insulate their bodies and reduce friction when they glide through the water.

10. Once a year, penguins experience a catastrophic molt. (Yes, that’s the official term.) Most birds molt (lose feathers and regrow them) a few at a time throughout the year, but penguins lose them all at once. They can’t swim and fish without feathers, so they fatten themselves up beforehand to survive the 2–3 weeks it takes to replace them.

An emperor penguin loses its old feathers (the fluffy ones) as new ones grow in underneath. Photo by Carlie Reum, National Science Foundation

11. Feathers are quite important to penguins living around Antarctica during the winter. Emperor penguins (Aptenodytes forsteri) have the highest feather density of any bird, at 100 feathers per square inch. In fact, the surface feathers can get even colder than the surrounding air, helping to keep the penguin’s body stays warm.

12. All but two penguin species breed in large colonies for protection, ranging from 200 to hundreds of thousands of birds. (There’s safety in numbers!) But living in such tight living quarters leads to an abundance of penguin poop—so much that it stains the ice! The upside is that scientists can locate colonies from space just by looking for dark ice patches.

13. Climate change will likely affect different penguin species differently—but in the Antarctic, it appears that the loss of krill, a primary food source, is the main problem. In some areas with sea ice melt, krill density has decreased 80 percent since the 1970s, indirectly harming penguin populations. However, some colonies of Adelie penguins (Pygoscelis adeliae) have grown as the melting ice exposes more rocky nesting areas.

14. Of the 17 penguin species, the most endangered is New Zealand’s yellow-eyed penguin (Megadyptes antipodes): only around 4,000 birds survive in the wild today. But other species are in trouble, including the erect-crested penguin (Eudyptes sclateri) of New Zealand, which has lost approximately 70 percent of its population over the past 20 years, and the Galapagos penguin, which has lost more than 50 percent since the 1970s.

  Learn more about the ocean from the Smithsonian’s Ocean Portal.

Flamingos depend on plant-derived chemical compounds to color their feathers, legs and beaks. Photo: Flickr user longhorndave

Pop quiz: Why are flamingos pink?

If you answered that it’s because of what they eat—namely shrimp—you’re right. But there’s more to the story than you might think.

Animals naturally synthesize a pigment called melanin, which determines the color of their eyes, fur (or feathers) and skin. Pigments are chemical compounds that create color in animals by absorbing certain wavelengths of light while reflecting others. Many animals can’t create pigments other than melanin on their own. Plant life, on the other hand, can produce a variety of them, and if a large quantity is ingested, those pigments can sometimes mask the melanin produced by the animal. Thus, some animals are often colored by the flowers, roots, seeds and fruits they consume

Flamingos are born with gray plumage. They get their rosy hue pink by ingesting a type of organic pigment called a carotenoid. They obtain this through their main food source, brine shrimp, which feast on microscopic algae that naturally produce carotenoids. Enzymes in the flamingos’ liver break down the compounds into pink and orange pigment molecules, which are then deposited into the birds’ feathers, legs and beaks. If flamingos didn’t feed on brine shrimp, their blushing plumage would eventually fade.

In captivity, the birds’ diets are supplemented with carotenoids such as beta-carotene and and canthaxanthin. Beta-carotene, responsible for the orange of carrots, pumpkins and sweet potatoes, is converted in the body to vitamin A. Canthaxanthin is responsible for the color of apples, peaches, strawberries and many flowers.

Shrimp can’t produce these compounds either, so they too depend on their diet to color their tiny bodies. Flamingos, though, are arguably the best-known examples of animals dyed by what they eat. What others species get pigment from their food? Here’s a quick list:

Northern cardinals and yellow goldfinches: When these birds consume berries from the dogwood tree, they metabolize carotenoids found inside the seeds of the fruit. The red, orange and yellow pigments contribute to the birds’ vibrant red and gold plumage, which would fade in intensity with each molt if cardinals were fed a carotenoid-free diet.

Salmon: Wild salmon consume small fish and crustaceans that feed on carotenoid-producing algae, accumulating enough of the chemical compounds to turn pink. Farmed salmon are fed color additives to achieve a deeper shades of red and pink.

Nudibranchs: These shell-less mollusks absorb the pigments of their food sources into their normally white bodies, reflecting the bright colors of sponges and cnidarians, which include jellyfish and corals.

Canaries: The birds’ normal diet doesn’t alter the color of its yellow feathers, but they can turn a deep orange if they regularly consume paprika, cayenne or red pepper. These spices each contain multiple carotenoids responsible for creating and red and yellow.

Ghost ants: There’s not much more than meets the eye with ghost ants: these tropical insects get their name from their transparent abdomens. Feed them water mixed with food coloring and watch their tiny, translucent lower halves fill up with brilliantly colored liquid.

Ghost ants sip sugar water with food coloring, which is visible in their transparent abdomens. Photo by Mohamed Babu/Solent News/Rex F/AP Images

Humans: Believe it or not, if a person eats large quantities of carrots, pumpkin or anything else with tons of carotenoids, his or her skin will turn yellow-orange. In fact, the help book Baby 411 includes this question and answer:

Q: My six-month-old started solids and now his skin is turning yellow. HELP!

A: You are what you eat! Babies are often first introduced to a series of yellow vegetables (carrots, squash, sweet potatoes). All these vegetables are rich in vitamin A (carotene). This vitamin has a pigment that can collect harmlessly on the skin, producing a condition called carotinemia.

How to tell that yellow-orange skin isn’t an indication of  jaundice? The National Institutes of Health explain that “If the whites of your eyes are not yellow, you may not have jaundice.”

Image via NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring

Last year, to celebrate the 42nd Earth Day, we took a look at 10 of the most surprising, disheartening, and exciting things we’d learned about our home planet in the previous year—a list that included discoveries about the role pesticides play in bee colony collapses, the various environmental stresses faced by the world’s oceans and the millions of unknown species are still out in the environment, waiting to be found.

This year, in time for Earth Day on Monday, we’ve done it again, putting together another list of 10 notable discoveries made by scientists since Earth Day 2012—a list that ranges from specific topics (a species of plant, a group of catfish) to broad (the core of planet Earth), and from the alarming (the consequences of climate change) to the awe-inspiring (Earth’s place in the universe).

Even the supposedly pristine Antarctic landscape is marred by trash heaps. Image via Germany Federal Environment Agency Report (PDF)

1. Trash is accumulating everywhere, even in Antarctica. As we’ve explored the most remote stretches of the planet, we’ve consistently left behind a trail of one supply in particular: garbage. Even in Antarctica, a February study found (PDF), abandoned field huts and piles of trash are mounting. Meanwhile, in the fall, a new research expedition went to study the Great Pacific Garbage Patch, counting nearly 70,000 pieces of garbage over the course of a month at sea.

2. Climate change could erode the ozone layer. Until recently, atmospheric scientists viewed climate change and the disintegration of the ozone layer as entirely distinct problems. Then, in July, Harvard researcher Jim Anderson (who won a Smithsonian Ingenuity Award for his work) led a team that published the troubling finding that the two might be linked. Some warm summer storms, they discovered, can pull moisture up into the stratosphere, an atmospheric layer 6 miles up. Through a chain of chemical reactions, this moisture can lead to the disintegration of ozone, which is crucial for protecting us from ultraviolet (UV) radiation. Climate change, unfortunately,  is projected to cause more of these sorts of storms.

3. This flower lives on exactly two cliffs in Spain. In September, Spanish scientists told us about one of the most astounding survival stories in the plant kingdom: Borderea chouardii, an extremely rare flowering plant that is found on only two adjacent cliffs in the Pyrenees. The species is believed to be a relic of the Tertiary Period, which ended more than 2 million years ago, and relies on several different local ant species to spread pollen between its two local populations.

4. Some catfish have learned to kill pigeons. In December, a group of French scientists revealed a phenomenon they’d carefully been observing over the previous year: a group of catfish in Southwestern France had learned how to leap onto shore, briefly strand themselves, and swim back into the water to consume their prey. With more than 2,000,000 Youtube views so far, this is clearly one of the year’s most widely enjoyed scientific discoveries.

5. Fracking for natural gas can trigger moderate earthquakes. Scientists have known for a while that whenever oil and gas are extracted from the ground at a large scale, seismic activity can be induced. Over the past few years, evidence has mounted that injecting water, sand and chemicals into bedrock to cause gas and oil to flow upward—a practice commonly known as fracking—can cause earthquakes by lubricating pre-existing faults in the ground. Initially, scientists found correlations between fracking sites and the number of small earthquakes in particular areas. Then, in March, other researchers found evidence that a medium-sized 2011 earthquake in Oklahoma(which registered a 5.7 on the moment magnitude scale) was likely caused by injecting wastewater into wells to extract oil.

6. Our planet’s inner core is more complicated than we thought. Despite decades of research, new data on the iron and nickel ball 3,100 miles beneath our feet continue to upset our assumptions about just how the earth’s core operates. A paper published last May showed that iron in the outer parts of the inner core is losing heat much more quickly than previously estimated, suggesting that it might hold more radioactive energy than we’d assumed, or that novel and unknown chemical interactions are occurring. Ideas for directly probing the core are widely regarded as pipe dreams, so our only options remains studying it from afar, largely by monitoring seismic waves.

The berries of Pollia condensata were found to produce the most intense color in the natural world. Image via PNAS

7. The world’s most intense natural color comes from an African fruit. When a team of researchers looked closely at the blue berries of Pollia condensata, a wild plant that grows in East Africa, they found something unexpected: it uses an uncommon structural coloration method to produce the most intense natural color ever measured. Instead of pigments, the fruit’s brilliant blue results from nanoscale-size cellulose strands layered in twisting shapes, which which interact with each other to scatter light in all directions.

8. Climate change will let ships cruise across the North Pole. Climate change is sure to create countless problems for many people around the world, but one specific group is likely to see a significant benefit from it: international shipping companies. A study published last month found that rising temperatures make it probable that during summertime, reinforced ice-breaking ships will be able to sail directly across the North Pole—an area currently covered by up to 65 feet of ice—by the year 2040. This dramatic shift will shorten shipping routes from North America and Europe to Asia.

9. One bacteria species conducts electricity. In October, a group of Danish researchers revealed that the seafloor mud of Aarhus’ harbor was coursing with electricity due to an unlikely source: mutlicellular bacteria that behave like tiny electrical cables. The organisms, the team found, built structures that traveled several centimeters down into the sediment and conduct measurable levels of electricity. The researchers speculate that this seemingly strange behavior is a byproduct of the way of the bacteria harvests energy from the nutrients buried in the soil.

Kepler 62f, discovered yesterday, is the most promising exoplanet candidate yet in terms of its potential to harbor life. Image via NASA/Ames/JPL-Caltech

10. Our Earth isn’t alone. Okay, this one might not technically be a discovery about Earth, but over the past year we have learned a tremendous amount about what our Earth isn’t: the only habitable planet in the visible universe. The pace of exoplanet detection has accelerated rapidly, with a total of 866 planets in other solar systems discovered so far. As our methods have become more refined, we’ve been able to detect smaller and smaller planets, and just yesterday, scientists finally discovered a pair of distant planets in the habitable zone of their stars that are relatively close in size to Earth, making it more likely than ever that we might have spied an alien planet that actually supports life.

Lashed to a spear made in the Gilbert Islands, researchers found a tooth from a dusky shark, a species previously unknown in the area. Image via PLOS ONE/Drew et. al.

For decades, a total of 124 swords, tridents and spears taken from the Pacific Ocean’s Gilbert Islands in the mid-1800s sat untouched in vaults in Chicago’s Field Museum. The weapons—each made up of dozens of individual shark teeth that islanders lashed to a wooden core with coconut fibers—were primarily considered artifacts of anthropological value.

Then, Joshua Drew, a marine conservation biologist at the museum, had an unusual idea: that the shark teeth lining the serrated blades could also serve as an ecological snapshot of the reefs that lined the islands more than a century ago. Sharks can be clearly identified solely by their teeth, so the teeth that islanders had harvested and used for their weapons might reflect historical biodiversity in the reefs that’s since been lost due to environmental degradation.

When Drew and others closely examined the hundreds of teeth on the weapons, they found that they came from eight different shark species, six of which were known to commonly swim in the Gilbert Islands’ waters. Two species, though—the dusky shark (Carcharhinus obscurus) and the spottail shark (Carcharhinus sorrah)—were something of a surprise. When the researchers looked at the scientific literature and various museum holdings of fish collected in the area, they found that these two species had never been documented within thousands of miles of the islands.

A trident lined with shark teeth, used in the study. Image via PLOS ONE/Drew et. al.

Drew calls this “shadow biodiversity”—a reflection of the life that lived in an ecosystem before we even started studying what was there. “[These are] hints and whispers of what these reefs used to be like,” he said in a press statement accompanying the paper documenting his team’s find, published today in PLOS ONE. “It’s our hope that by understanding how reefs used to look we’ll be able to come up with conservation strategies to return them to their former vivid splendor.”

Working with Mark Westneat, the museum’s curator of fishes, and Christopher Philipp, who manages the anthropology collections, Drew classified each tooth on every weapon by shark species, primarily using field guides and photos. In cases where the tooth’s identity was ambiguous, he made use of the Museum’s own ichthyological holdings, comparing it to preserved specimens from each shark species.

Because dusky and spottail shark teeth were found on the weapons—crafted sometime between the 1840s and 1860s, shortly before they were collected—the researchers believe these two species were once part of the ecosystem and have since been eradicated. There is the possibility that the teeth were harvested elsewhere and came to the Gilbert Islands via trade, but the team says it’s unlikely.

For one, sharks figure largely in the islanders’ traditional culture, and it’s well-known that they had effective shark-fishing techniques, making it unlikely that they’d go to the trouble of exporting teeth from afar. The two species’ teeth were among the most common found on the weapons, so it also stands to reason that they were fairly abundant nearby. Secondly, there is no historical or archaeological evidence that trade occurred between the extremely remote Gilbert Islands and either the Solomon Islands (the closest known location of spottail sharks) or Fiji (for dusky sharks).

It’s impossible to know for sure, but given the environmental degradation that’s occurred over the past century in the Pacific’s coral reefs, the researchers suspect that humans played a role in these sharks’ local eradication. Because sharks mature slowly and have a small number of offspring per individual, they can be wiped out quickly by moderate levels of fishing, and the commercial shark fishing industry started up in the area as early as 1910.

Rigorous fish surveys of the Pacific didn’t begin for a few more decades, so these weapons—and perhaps other human artifacts that incorporate biological specimens—serve as a valuable time capsule of the ecosystems that predated scientific study. Drew thinks that the “shadow diversity” we’ve since lost should inspire people in the marine conservation field to recreate the biodiversity that predates the Industrial Age.

“When we set up modern conservation plans, we shouldn’t sell ourselves short,” he told Nature last year, when he revealed his preliminary results at a conference. “We might not recapture the vivid splendor of those super-rich levels, but this information argues for setting up management plans to protect what sharks are there.”

Beneath the seafloor, there is an ecosystem of microbes living in the oceanic crust, independent of sunlight. Here, the seafloor of McMurdo Sound in Antarctica. NSF/USAP photo by Steve Clabuesch

If you were to hit the seafloor and continue to travel down, you’d run into an ecosystem unlike any other on earth. Beneath several hundred meters of seafloor sediment is the Earth’s crust: thick layers of lava rock running with cracks that cover around 70% of the planet’s surface. Seawater flows through the cracks, and this system of rock-bound rivulets is enormous: it’s the largest aquifer on earth, containing 4% of global ocean volume, says Mark Lever, an ecologist who studies anaerobic (no-oxygen) carbon cycling at Aarhus University in Denmark.

The sub-seafloor crust may also be the largest ecosystem on earth, according to a new study by Lever, published this month in Science. For seven years, he incubated 3.5 million-year old basalt rock collected from 565 meters below the ocean floor–the depth of nearly two stacked Eiffel towers–and found living microbes. These microbes live far away from the thriving bacterial communities at mid-ocean ridges, and survive by slowly churning sulfur and other minerals into energy.

But just how big is this chemically-fueled ecosystem that survives entirely without oxygen? If the results from his sample, collected from below the seafloor off the coast of Washington state, are similar to those found across the planet, then diverse microbial communities could survive throughout the ocean’s crust, covering two-thirds of the earth’s surface and potentially going miles deep.

The sub-seafloor crust has plenty of space and energy-rich minerals–a welcoming potential habitat for a large microbial community–“but we have no idea what the ecosystem looks like,” says Julie Huber, a microbial oceanographer at the Marine Biological Laboratory in Woods Hole, Massachusetts. “Mark’s evidence would point to it being a very different world.”

Microbes that get their energy from minerals, rather than from sunlight, are far from rare. The most well known of these so-called chemoautotrophic or chemosynthetic bacteria are those found at hydrothermal vents in the deep sea. Some of these bacteria live symbiotically with giant tubeworms, mussels and clams, providing chemically-produced energy to these larger organisms as they “breathe” the sulfur-rich water erupting from the vent–not unlike how plants convert sunlight into energy at the surface. Chemosynthetic microbes are also found in the rotting and oxygen-poor muck of salt marshes, mangroves and seagrass beds—“any place you’ve got stinky black mud, you can have chemoautotrophy,” says Chuck Fisher, a deep-sea biologist at Pennsylvania State University in College Park.

But what makes Lever’s sub-seafloor microbes different is that they don’t use any oxygen at all. The symbiotic bacteria at hydrothermal vents are often described as “life without sunlight,” but they still rely on sunlight indirectly by using sun-produced oxygen in the chemical reaction to generate energy. Chemosynthetic microbes in salt marshes feed on decomposing plants and animals, which got their energy from sunlight. Even deep-sea sediment is accumulated from an assortment of dead animals, plants, microbes and fecal pellets that relies on light energy.

The oceanic crust microbes, on the other hand, rely entirely on non-oxygen-containing molecules derived from rock and completely removed from photosynthesis, such as sulfate, carbon dioxide and hydrogen. “In that sense it’s a parallel universe, in that it runs on a different type of energy,” says Lever. These molecules provide a lot less energy than oxygen, creating a sort of microbial slow food movement. So instead of dividing and growing quickly like many oxygen-based bacteria, Fisher suspects that microbes in the Earth’s crust may divide once every hundred or thousand years.

A hydrothermal vent, covered with tube worms, spews black sulfur smoke on the Juan de Fuca Ridge. The oceanic crust microbes were collected hundreds of meters under the seafloor beneath this same ridge. Photo via University of Washington; NOAA/OAR/OER

But just because they’re slow doesn’t mean they’re uncommon. “There are lots of data that there is a large, very productive biosphere under the surface,” says Fisher.

In addition, microbial population sizes in different areas of the crust may vary greatly, Huber notes. Through her studies on the fluid found between the cracks in the crust,  she says that in some areas the fluid contains about the same number of microbes as standard deep-sea water collected at ocean depths of 4,000 meters (2.5 miles): around 10,000 microbial cells per milliliter. In other regions, such as at the Juan de Fuca Ridge in the Pacific Ocean where Lever found his microbes, there are fewer cells, around 8,000 microbes per milliliter. And in other regions, such as in non-oxygenated fluid deep in hydrothermal vents, there can be around 10 times more.

It’s not just the number of microbes that vary depending on location–it’s possible that different microbial species are found in different types of crust. “Different types of rock and different types of chemistry should result in different types of microbes,” says Andreas Teske, a deep-sea microbial ecologist at the University of North Carolina at Chapel Hill and co-author on Lever’s paper. The Juan de Fuca Ridge is a relatively hot area bursting with new rock, which tends to be made of more reactive minerals and thus able to provide more energy. Other parts of the crust are older, composed of different minerals, and cooler. And, in some regions, oxygenated water reaches down to the cracks.

It’s this infiltrating seawater that keeps this sub-seafloor ecosystem from existing on a completely separate plane from our oxygenated one. “The crust plays a significant role in influencing the chemical composition of the ocean and the atmosphere, ultimately influencing [nutrient] cycles on earth,” says Lever. Some of the compounds created by oceanic crust microbes from rock are water soluble, and will eventually enter the ocean. Sulfur, for example, is present in magma—but after the microbes use it for energy, it’s converted to sulfate. Then it dissolves and becomes an important nutrient in the ocean food chain.

Lever’s find of a microbial community in the crust could catalyze the scientific community to answer these questions. For example, what kinds of microbes are found where, do they interact through interconnected cracks in the rock, and what role do they play in mineral and nutrient cycling? In some ways, it’s very basic exploratory work. “A lot of what we do on the seafloor is similar to what we’re doing on Mars right now,” says Huber. “Controlling [NASA’s Mars Rover] Curiosity is very similar to operating an ROV under the ocean.”

  Learn more about the deep sea from the Smithsonian’s Ocean Portal.

An island of ice breaking away from Greenland’s Petermann Glacier (in the center of the photo)  in the summer of 2010. By NASA

On the morning of July 16, 2010, a hunk of ice four times the size of Manhattan cracked away from the tongue of Greenland’s Petermann Glacier and drifted to sea as the largest iceberg since 1962. Just two years later, another massive section of ice calved from the same glacier. Icebergs like these don’t stay put in the Arctic–they get picked up by currents and ushered to warmer climates, melting along the way.

According to a new study published in the journal Geophysical Research Letters, Greenland’s melting glaciers and ice caps sent 50 gigatons of water gushing into the oceans from 2003 to 2008. This comprises about 10 percent of the water flowing from all ice caps and glaciers on Earth. The research comes on the heels of a study last year that showed the ice sheets of Greenland and Antarctica are disappearing three times faster than in the 1990s, and that Greenland’s is melting at an especially accelerated rate. In the new study, scientists were able to put an even finer point to the ice-melt situation by separating out the glaciers and ice caps from the ice sheet, which blankets 80 percent of the island. What they discovered is that Greenland’s glaciers are actually melting more quickly than the ice sheet.

Studies such as these demonstrate the impacts of a warming climate on Greenland’s glaciers. But, as they say, a picture is worth a thousand words. Visual evidence of this liquefaction is captured by NASA satellites, which are able to take snapshots of calving glaciers and document longer-term ice melt. NASA displays photos of the glaciers in its State of Flux photo gallery, along with a rotating collection of satellite images that illustrate other changes to the environment, including wildfires, deforestation and urban development.

The photos, with their “now-you-see-it, now-you-don’t” quality, illustrate how glaciers are fast becoming ephemeral. Here are a few stark examples:

Greenland’s Helheim Glacier can be seen retreating and thinning from 2001 (left) to 2003 (center) to 2005 (right). By NASA 

The set of images above shows the edge of Greenland’s Helheim Glacier, located on the fringe of the Greenland Ice Sheet, as captured by a satellite in 2001, 2003 and 2005. The calving front is marked by the curved line through the valley, while bare ground appears brown or tan and vegetation is red.

According to NASA, when warmer temperatures initially cause a glacier to melt, it can spark a chain reaction that accelerates the thinning of the ice. As the edge of the glacier begins to liquefy, it crumbles, creates icebergs and eventually disintegrates. The loss of mass throws the glacier off balance, and further thinning and calving occurs, a process that stretches the glacier through its valley. Total ice volume decreases then shrinks the glacier as calving carries ice away. Helheim’s calving front stayed put from the 1970s until 2001, at which point the glacier began hasty cycles of thin, advance, and dramatic retreat, ultimately moving 4.7 miles toward land by 2005.

Greenland’s Petermann Glacier on June 26, 2010 (left) , before a massive iceberg broke away, and on August 13, 2010, after the break. By NASA

The massive calving event at Petermann Glacier in 2010 is pictured in these two images. The glacier is the white ribbon on the right side of each photo, and its tongue extends into the Nares Strait, which appears as a bluish-black stripe across the center of the right image and is heavily flecked with white chunks in the photo on the left. In the first image, the tongue of the glacier is intact; in the second, a huge chunk of ice has broken off and can be seen floating away through the fjord. This iceberg was 97 square miles in size–four times bigger than the island of Manhattan.

Greenland’s Petermann Glacier on July 16, 2012 (left and center), before a major calving event, and July 17, 2012, after an iceberg broke off. By NASA

In the summer of 2012, a second massive iceberg crumbled away from the Petermann Glacier. In these images, the glacier is the white ribbon snaking up from the bottom right. If you follow the tongue up, you’ll see that it appears intact in the photos at left and center (though the center image has an ominous crack spanning its width), which were taken the day before the calving occurred. The photo on the right shows that it crumbled as the glacier calved.

Given that Greenland experienced an exceptionally warm summer in 2012 and temperatures were higher than average this winter, 2013 is primed for more melting and massive icebergs. Last year’s ice-melt season lasted two months longer than the average since 1979, and this year’s is already off to an inauspicious start. It kicked off on March 13 with the sixth-smallest sea-ice area on record for Greenland, according to the National Snow and Ice Data Center. What will the new summer calving season bring?

Polar bear-brown bear hybrids like this pair at Germany’s Osnabrück Zoo are becoming more common as melting sea ice forces the two species to cross paths. Photo by Corradox/Wikimedia Commons

Scientists and science writers have created catchy monikers for hybrid species, much the way tabloid writers merge the names of celebrity couples (Kimye, Brangelina, anyone?). Lions and tigers make ligers. Narwhals meet beluga whales in the form of narlugas. And pizzlies and grolar bears are a cross between polar bears and grizzlies. In coming years, their creativity may get maxed out to meet an expected spike in the number of hybrids. A driving force? Climate change. 

A new study published in the journal PLOS Genetics showed that there’s a historic precedent for cross-breeding among polar bears and brown bears–we’ll jump on the bandwagon and call them brolar bears. The researchers also asserted that such hybridization is currently occurring at an accelerated clip. As sea ice melts, polar bears are forced ashore to an Arctic habitat that’s increasingly hospitable to brown bears. There have been recent sightings in Canada of the resulting mixed-breed animals, which have coloring anomalies such as muddy-looking snouts and dark stripes down their backs, along with the big heads and humped backs typical of brown bears.

As it turns out, climate-change-induced hybridization extends well beyond bears. A 2010 study published in the journal Nature listed 34 possible and actual climate-change-induced hybridizations (PDF) of Arctic and near-Arctic marine mammals–a group that has maintained a relatively consistent number of chromosomes over time, making them particularly primed for hybridization. Here are some highlights from this list, along with some more recent discoveries. 

In 2009, a bowhead-right-whale hybrid was spotted in the Bering Sea by the National Oceanic and Atmospheric Administration’s (NOAA) National Marine Mammal Laboratory. Right whales, which typically hail from the North Pacific and North Atlantic, will increasingly be migrating north into the Arctic Ocean, the domain of bowheads, as a result of climate change–and co-mingling their DNA. The authors of the Nature study determined that “[d]iminishing ice will encourage species overlap.”

The narluga has a very big head, according to the scientists who found one in West Greenland. Its snout and lower jaw were particularly burly, and its teeth shared some similarities with both narwhals and belugas. Both species, which form a whale family called monodontidae, live in the Arctic Ocean and hunters have reported seeing more whales of similar stature in the region.

Harbor and Dall’s porpoises have already been mixing it up off the coast of British Columbia, and given that harbor porpoises are likely to keep moving north from the temperate seas of the North Atlantic and North Pacific into the home waters of the Dall’s, the trend is expected to continue. (Click here to see rare photos of the hybrid porpoise.)

Scientists in Ontario, Canada, are investigating inter-breeding between southern and northern flying squirrels as the southern rodents push into northern habitats. The hybrid squirrels have the stature of the southern species and the belly coloring of the northern one. The video below details the research.

Hybrid species often suffer from infertility, but some of these cross-breeds are having success at procreating. For example, researchers recently discovered the offspring of a female pizzly and a male grizzly bear (a subspecies of the brown bear) in Canada’s Northwest Territories. Despite cases like these, scientists are debating whether all of this hybridization is healthy. “Is this going to be a problem for the long-term existence of parental species? Are they going to merge into one big hybrid population?” asked University of California, Berkeley evolutionary biologist Jim Patton in an interview.

In the case of inter-bred polar bears, the concern is that the changing climate will be more welcoming to brown bears, and that while inter-species mating at first might appear to be an adaptive technique for polar bears, it could end up spelling their demise in all ways except cellular structure–much the way Neanderthals were folded into the human gene pool thanks to early humans in Europe more than 47,000 years ago.

Rare and endangered species are particularly vulnerable to the pitfalls of hybridization, according to the authors of the Nature study. “As more isolated populations and species come into contact, they will mate, hybrids will form and rare species are likely to go extinct,” they wrote. “As the genomes of species become mixed, adaptive gene combinations will be lost.”

Such is likely the case with the narluga. Scientists determined the animal’s lack of a tusk is a liability because the tusk is a measure of the narwhal’s breeding prowess. And a pizzly living at a German zoo showed seal-hunting tendencies, but lacked the swimming prowess of polar bears.

As Patton pointed out, it will be many years until we know the full consequences of hybridization. “We’re only going to find out in hindsight,” he said. But that’s not a reason to be complacent, according to the Nature authors, who called for the monitoring of at-risk species. “The rapid disappearance of sea ice,” they wrote, “leaves little time to lose.”

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A model of a giant squid versus sperm whale. Photo taken at the American Museum of Natural History by Mike Goren from New York

For centuries, monsters of the deep sea captivated the imagination of the public and terrified explorers–none more so than the many-tentacled kraken. In 13th century Icelandic sagas, the Vikings wrote of a terrifying monster that “swallows both men and ships and whales and everything that it can reach.” Eighteenth century accounts from Europe describe arms emerging from the ocean that could pull down the mightiest ships, attached to bodies the size of floating islands.

Today, we’re fairly confident that a tentacled beast will not emerge from the depths to swallow up a cruise ship, but the enduring allure of such creatures lingers. None of the ocean’s massive animals, perhaps, are as intriguing as the giant squid.

Now, scientists have come one step closer to unraveling the mysteries behind this rare animal. As it turns out, contrary to some squid enthusiasts’ former hypothesis, all giant squid belong to a single species. What’s more, those animals are extremely similar genetically.

To arrive at these findings, researchers from the University of Copenhagen’s Natural History Museum of Denmark along with collaborators from 7 other countries genetically analyzed bits and pieces of 43 of the animals–which can grow more than 40 feet long and weigh nearly 2,000 pounds–recovered from all over the world.

Photo by Winkelmann et. al.

Their results indicated that, unlike most marine animals, giant squid harbor almost no genetic diversity. Remarkably, individuals as far apart as Florida and Japan, from a statistical standpoint, shared almost the same DNA. The giant squid’s genetic diversity turned out to be 44 times lower than the Humboldt squid, another large species, and seven times lower than the diversity of a population of oval squids living in a restricted area and thus prone to inbreeding. In fact, the giant squid’s diversity was lower than all other measured oceanic species, save the basking shark, which scientists believe recently underwent a severe population bottleneck in which most animals died and only a few individuals survived and repopulated the species.

The researchers can only speculate about this finding’s underlying reasons–the giant squid’s genetic data alone cannot provide a plausible explanation. Perhaps something about the giant squid makes it advantageous to cull mutations from its genome? Alternatively, the animals may have undergone a recent bottleneck, similar to what happened to the basking sharks, meaning that all giant squid following that event are closely related. Or perhaps a few foundered squid somehow wandered in new stretches of ocean, so when they populated these new habitats their offspring shared the same squid family tree. The short answer, however, is that the researchers simply do not know.

“We cannot offer a satisfactory explanation for the low diversity, and this requires future studies to resolve,” they write in a paper published this week in Proceedings of the Royal Society B.

This has been a big year for giant squid. In January, a Japanese team released the first footage of a giant squid interacting in its natural environment. Yet much still remains to be learned about these enigmatic creatures. For example, researchers still have no idea how large of a range the adult squid patrol, how long they live, how quickly they grow and whether problems such as climate change affect their populations.

For the imagination’s sake, however, perhaps it’s best if some mysteries endure.

“Despite our findings, I have no doubt that these myths and legends will continue to get today’s children to open their eyes up–so they will be just as big as the real giant squid is equipped with to navigate the depths,” said lead researcher Tom Gilbert in a statement. 

At the bottom of the Mariana Trench, nearly eight miles below the ocean’s surface, abundant communities of bacteria thrive. Image via PNAS/Yayanos et. al.

The Challenger Deep, the deepest point on the entire seafloor, lies in the Mariana Trench off the coast of the Pacific Ocean’s Mariana Islands. It is nearly 36,000 feet—6.8 miles—below the ocean’s surface. If you were to stand at this remarkable depth, the column of water above your head would exert 1000 times the amount of pressure you normally experience at the surface, crushing you instantly.

Even in this extreme environment, though, organisms can survive. One type, it turns out, can even prosper: bacteria. A new study, published today in Nature Geoscience, finds that unexpectedly abundant bacteria communities grow in the depths of the Mariana Trench, with organisms living at densities ten times greater than in the much shallower ocean floor at the trench’s rim.

To probe the ultra-deep ecosystem, the international research team, led by Ronnie Glud of the University of Southern Denmark, sent a specially-designed, 1300-pound robot down to the bottom of the trench in 2010. The robot was equipped with thin sensors that can slice into the seafloor sediments to help measure the organic consumption of oxygen. Because living things consume oxygen as they respire, tallies on how much ambient oxygen is missing from the sediments can be used as a proxy for the amount of microorganisms living in that area.

The research team’s specialized robot, designed to take samples under extremely high pressure. Photo by Anni Glud

When the team used the device to sample the sediments at a pair of sites with depths of 35,476 and 35,488 feet, they found surprisingly high amounts of oxygen consumption—levels that indicated there were ten times more bacteria present at the ultra-deep site than at another, shallower site they sampled for reference about 37 miles away, at a depth of just 19,626 feet.

The robot also collected a total of 21 sediment cores from the two sites, and these cores were hauled up and analyzed in the lab. Although many of the microorganisms died when they were brought up to the surface—after all, the creatures are adapted for the high pressure and low temperature of the ocean floor—the finding was confirmed: Cores from the Mariana Trench had much higher densities of bacterial cells than those from the reference site.

The team also remotely recorded video of the ocean floor, using lights to illuminate the pitch-black environment, and found a few life forms much larger than bacteria scurrying around on top of the sediment. When they used baited traps to recover a few of the specimens and bring them to the surface, they determined they were Hirondellea gigas, a species of amphipods—small crustaceans typically less than an inch in length.

A video still from the seafloor reveals an amphipod (left) scurrying across the bacteria-filled sediment. Image via Nature Geoscience/Glud et. al.

The discovery of such abundant bacterial life is particularly surprising because conventional wisdom would suggest that not enough nutrients are present at such depths to support much growth. Photosynthetic plankton serve as the nutrient base for nearly any ocean food chain, but they’re unable to survive on the lightless seafloor. The waste products (such as dead animals and microorganisms) of ecosystems higher up in the shallow light-filled waters do filter down and feed deeper food webs, but typically, less and less organic matter makes it down as depths increase.

In this case, though, the scientists seem to have found an exception to the rule, since the ultra-deep trench was home to so much more bacterial activity than the nearby shallower reference site. Their explanation is that the trench acts as a natural sediment trap, gradually collecting nutrients that filter down and land at shallower locations on the ocean floor nearby, then are dislodged by earthquakes or other perturbations.

In the years since the 2010 exploration, the research team has sent the same robot down to sample the Japan Trench (roughly 29,500 feet deep) and plans to sample the Kermadec-Tonga Trench (35,430 feet deep) later this year. “The deep sea trenches are some of the last remaining ‘white spots’ on the world map,” Glud, the lead author, said in a press statement. “We know very little about what is going on down there.”

Ribbon worms come in all shapes and sizes. This one, with white stripes along the body, was found off the coast of Mexico. Photo by Chris Meyer and Allen Collins

Whether they’re on a rain-soaked sidewalk, in the compost bin or on the end of a fish hook,  the worms most people know are of the segmented variety. But what about all the other worms out there?

With more than 1,000 species of ribbon worms (phylum Nemertea), most found in the ocean, there is a huge range of sizes and lifestyles among the various types. A defining characteristic of ribbon worms is the presence of a proboscis—a unique muscular structure inside the worm’s body. When attacking prey, they compress their bodies to push out the proboscis like the finger of a latex glove turned inside-out.

Here are 14 other fun facts about them:

1. The largest species of ribbon worm is the bootlace worm, Lineus longissimus, which can be found writhing among rocks in the waters of the North Sea. Not only is it the largest nemertean, but it may also be the longest animal on the planet! Uncertainty remains because these stretchy worms are difficult to accurately measure, but they have been found at lengths of over 30 meters (98 feet) and are believed to even grow as long as 60 meters (197 feet)—longer than the blue whale! Despite their length they are less than an inch around.

An illustration of a bootlace worm, which can be found at lengths of 30 meters (98 feet) or longer. From McIntosh/Publisher Selam Amare

2. The smallest ribbon worm species is less than a centimeter long, and resembles a piece of thread more closely than what we think of as a worm.

3. Ribbon worms have highly developed muscles that allow them to contract their bodies, shrinking to a tenth of their extended length when threatened.

4. Talk about stretching: ribbon worm muscles don’t just contract–they can also expand, allowing some species to swallow prey (such as other kinds of worms, fish, crustaceans, snails and clams) that are more than double the width of their narrow bodies

Ribbon worm (Nemertean) eating a polychaete annelid [edited] from LabNemertea on Vimeo.

5. The proboscis varies among the species. Some are sticky or have suckers to help grasp prey, and some species, like those in the order Hoplonemertea, even stab their prey with a sharp spike, called a stylet, on the proboscis.

6. Because the stylets often are lost during an attack, the worms continually make and use replacements that they have in reserve in internal pouches.

7. As a second line of defense, many ribbon worms are poisonous and taste bad. Several species contain tetrodotoxin, the infamous pufferfish venom that can induce paralysis and death by asphyxia. It’s still not known exactly how the toxins are produced—they may linger in the worms from ingested bacteria—but they deter predators from taking a bite. Some even eject toxins from their proboscis.

8. Some ribbon worms sneak up on their prey, lying in wait buried in the sandy seafloor. One species of worm will pop up from its home in the sand when a fiddler crab walks over. The worm will cover the prey with toxic slime from its proboscis, paralyzing the crab so the ribbon worm can slide into a crack in the shell and eat the crab from the inside out.

9. Not all ribbon worms are predators – some are parasites. One genus of ribbon worms, Carcinonemertes, lives as a parasite on crabs, eating the crab’s eggs and any animals that it can find from the confines of its host.

A parasitic ribbon worm, seen in this picture with the crab eggs it persists on.
Photo by Sadeghian and Santos

10. Most ribbon worms produce a slippery mucus that covers their bodies and helps them to navigate through the mud and rocks on the ocean floor.

11. Some also use the mucus as a protective coat to keep from drying out when exposed to air during low tides. Others use their proboscis to move by attaching it to an object and pulling themselves forward. This same mucus makes them hard to catch! And not only by predators: scientists trying to catch the worms have a difficult time.

12. Marine ribbon worms usually have separate sexes and temporary sex organs. Rows of gonads line the inside of their bodies to produce either eggs or sperm. When they are ready to be released, the gonad ducts form on demand and are reabsorbed after reproduction.

13. Most ribbon worms have direct development: a miniature version of the worm hatches from a fertilized egg. However, the young of one group of ribbon worms, the heteronemerteans, emerge in a bizarre larval stage that looks like a flying saucer. After a few weeks to months living and feeding in the open ocean, a small worm develops inside and, when it’s ready, it eats its way out of the original larva encasing. Then the worm falls to the sea floor where it spends the rest of its life.

14. Many ribbon worms can regenerate when a predator takes a bite, healing their broken ends. One worm species, Ramphogordius sanguineus, has an exceptional ability to regenerate: if any part of their body is severed (except for the very tip of their tail where there are no nerves), it can regrow into a new worm. This new individual may be smaller than the worm it came from, but more than 200,000 worms can result from an individual that is only 15 centimeters (6 inches) long!

 Learn more about the ocean from the Smithsonian’s Ocean Portal. 

Warming oceans have caused levels of phytoplankton, like the mixed sample of single-celled and chain-forming diatoms pictured above, to decline 40 percent since 1950. Photo by Richard Kirby

Two weeks ago, a group of sailors off the coast of New Zealand leaned over the side of their boat, dropped a contraption into the Pacific Ocean and watched it disappear. Using an app they’d downloaded to a smartphone, they logged a reading from the underwater device, along with their GPS location and the water temperature. In just a few minutes’ time, they had become the first participants in a new program launched by the UK’s Plymouth University Marine Institute which allows citizen scientists to help climatologists study the effects of climate change on the oceans.

The Kiwi sailors were measuring the concentration of phytoplankton, a microorganism that lives at the sea surface. Phytoplankton, also called microalgae, produce half of the oxygen in the air we breathe and are responsible for 50 percent of the Earth’s photosynthesis. Whales, jellyfish, shrimp and other marine life feast on it, making it a critical part of the marine food chain.

Phytoplankton require a certain water temperature to thrive (this varies regionally), and without these favored conditions, they either decrease in number or migrate in search of optimal water. As the upper levels of the Earth’s oceans have warmed by 0.59 degrees Fahrenheit in the past century, the amount of phytoplankton worldwide dips by roughly 1 percent each year, according to a 2010 study published in the journal Nature

In fact, the study showed that phytoplankton concentrations have decreased by a total of 40 percent since 1950. The decline joins coral bleaching, sea-level rise, ocean acidification and a slowing of deep-water circulation (which effects water temps and weather patterns) as the known tolls of climate change on the oceans.

This drop in phytoplankton population is troubling because of this organism’s role in the marine food web. “Despite their microscopic size, phytoplankton… are harbingers of climate change in aquatic systems,” wrote the authors of a 2011 study on phytoplankton and climate change published in the journal Proceedings of the Royal Society. So understanding how other sea creatures will fare as climate changes depends on how drastically phytoplankton levels continue to drop.

The effects of a food shortage on big, open-ocean fish like swordfish and tuna, which already suffer from over-fishing, could pose problems for humans as well. “We’re squeezing [fish] from both ends,” Paul Falkowski, who runs the Rutgers University Environmental Biophysics and Molecular Ecology Lab, told Nature. “We’re overfishing the oceans for sure. Now we see there is pressure from the bottom of the food chain.”

Despite it’s importance, scientists have struggled to monitor phytoplankton, and analyzing all of the Earth’s oceans presents obvious logistical hurdles. Those challenges became apparent after one recent study concluded climate change is not to blame for dwindling phytoplankton levels and another refuted that phytoplankton is vanishing at all–igniting debate within the scientific community. Enter the Plymouth study, which is attempting to end the dispute and fill in gaps in phytoplankton research by harnessing the millions of sailors and fishermen who cruise the world’s oceans to help measure phytoplankton levels in the upper reaches of the water.

The program relies on the Secchi app, a new smartphone app devised by the Plymouth scientists that’s named for the Secchi Disk (PDF)—a piece of equipment that’s been used to measure turbidity in water since its invention in 1865 by Italian scientist Pietro Angelo Secchi. “It’s arguably the simplest item of marine sampling equipment,” Plymouth’s Richard Kirby, a plankton biologist who’s heading up the project, told Surprising Science.

Plankton biologist Richard Kirby lowers a Secchi Disk into Britain’s Plymouth Sound. Photo courtesy of Richard Kirby

When a seafaring citizen scientist is ready to use the app, the first step is to make a Secchi Disk (instructions are included). The small, white disk–made of plastic, wood or metal–is attached to a tape measure on one side and a weight on the other. You hold the tape measure and lower the disk vertically into the seawater, and as soon as it disappears from sight, you note the depth on the tape measure. This number, the “Secchi depth,” reflects the transparency of the water column, which is influenced by the number of particles present. “Away from estuaries and areas where the turbidity of the water column may be influenced by suspended sediment, the Secchi Depth is inversely related to phytoplankton biomass,” Kirby says. The Secchi depth also tells scientists the depth to which light supports life in the water.

You enter the Secchi depth and the GPS location on your smartphone (a network connection isn’t required for this) into the app. The Plymouth researchers receive the data as soon as you regain network connectivity. You can also upload photos and type in additional details like water temperature (measured by the boat) and notes on visual observations–say, a foamy surface, a plankton bloom or a flock of feeding sea birds.

A Secchi Disk submerged in Britain’s Plymouth Sound. Photo by Richard Kirby

The Plymouth researchers hope ocean-goers across the globe will participate in the research, with which they will build a database and a map of the oceans charting both the seasonal and annual changes in phytoplankton levels to help scientists studying climate change and the oceans. “One person recording a Secchi depth twice a month for a few years will generate useful data about their local sea,” Kirby says. “The more people that take part, the greater the project and the more important and valuable it will become to future generations.”

Kirby notes that citizen scientists have long provided valuable data on long-term changes to the environment, and sees the internet as big opportunity to unite the efforts of citizen scientists. “We often look back and wish we had started monitoring something about the natural world,” he says. “‘If only we had started measuring ‘x’ ten years ago.’ Well, there is no time like the present to start something for the future.”

Fluorescent proteins all aglow in these corals. Photo by Michael Lesser and Charles Mazel, NOAA Ocean Explorer

Anyone who has gone scuba diving or snorkeling in a coral reef will likely never forget the dazzling colors and other-worldly shapes of these underwater communities. Home to some of the world’s most diverse wildlife hotspots, reefs are worth an annual $400 billion in tourist dollars and in the ecosystem services they provide, such as buffering shores from storms and providing habitat for fish that people eat.

Yet it’s a well known fact that coral reefs around the world are in decline thanks to pollution and rapidly warming oceans. However, determining just how reefs are faring–and designing steps to protect them–requires a way to accurately measure their health. Researchers tend to rely upon invasive, damaging techniques to figure out how corals are coping, or else they perform crude spot checks to determine reef health based on coral color alone.  But now, scientists have announced a new method of determining coral health that relies upon measuring the intensity of corals’ fluorescent glow.

Yes, glow. Corals naturally produce fluorescent proteins which glow an eery green when seen under a blue light–nearly all corals exhibit this physiological phenomenon.

“This is the first study to follow the dynamics of coral fluorescence and fluorescent protein levels during temperature stress, and shows that coral fluorescence could be utilized as a early indicator of coral stress,” said Melissa Roth, a marine biologist at the University of California, Berkeley (formerly of the Scripps Institution of Oceanography at the University of California, San Diego), in an email. “Because coral fluorescence can be measured non-invasively in the field, it could be an important tool for management of reefs,” she said. Roth and her colleague Dimitri Deheyn described their findings this week in Scientific Reports.

The degree to which a coral glows depends largely on another group of organisms, dinoflagellate algae. Corals are actually a symbiotic assembly of itself and these microscopic dinoflagellate algae–the dinoflagellates help corals attain nutrition, which in turn fuels the growth of coral reefs. The tiny organisms are also responsible for giving corals their typical brownish hue.

But dinoflagellates can abandon ship due to stressors such as increased temperature, a phenomenon known as coral bleaching. Left on their own without the aid of their dinoflagellate covering, the corals’ naturally white skin becomes glaringly visible. The coral can live for a little while after a dinoflagellate exodus, but not for long. If the algae do not return, the coral will die.

Knowing this, Roth and Deheyn decided to investigate how coral fluorescence might reflect the current state of a coral and its dinoflagellates’ relationship. They chose to use Acropora yongei, a common branching coral, in their experiments since it’s often one of the first corals shows signs of stress and bleaching in a reef. They subjected individual corals to one of two different experimental setups in their lab. In some containers, they pummeled corals with cold water, and in others they doused corals in hot water. Another group of corals served as a control. Then they let the corals pickle in their temperature-regulated waters for almost three weeks. 

The researchers found a distinct correlation between the degree of bleaching and the concentration of a coral’s fluorescent proteins, which in turn determined the strength of it’s glow. In the first 4 to 5 days, the fluorescent protein concentration and glow of both cold and heat-treated corals dropped. But by the end of the 20-day experiment, cold-stressed corals had acclimated and recovered to their normal level of fluorescence. Heat-stressed corals, on the other hand, bleached and began to glow even more strongly, probably because their dinoflagellate communities no longer blocked the coral’s underlying fluorescence. Like a supernova before a star’s final collapse, the corals send out a steady stream of intense glow just before their inevitable demise.

Corals pictures under white light (left panels) and blue light (right panels) show how corals subjected to heat stress eventually bleached and increased their fluorescent glow by the end of the experiment. Photo by Melissa Roth, Scientific Reports

After death, the glow stops. In a reef system, the bone white coral would gradually get masked by a film of green algae that coats the ruins of the now deceased organism.

Once corals start to bleach, conservationists or wildlife managers have few options for helping reefs as they begin to decline and often eventually die. But if they catch the problem ahead of time, they could try to help the coral with strategies such as shading with artificial structures or sediments, adding antioxidants to the water or introducing heartier dinoflagellates, though scientific studies validating these potential rescue methods are largely lacking. 

This new finding, Roth hopes, can be used to preempt reef collapse, serving as a sort of canary in the coal mine for corals in distress. “Managers could focus on the most sensitive corals on a reef, like branching corals, and look for rapid drops in fluorescence as an early sign of stress,” Roth said. This would give them about a week-long window to take action before full-blown bleaching began. “Bleaching would be like a heart attack,” she explained. “You would rather detect signs of high blood pressure or clogging of the arteries to address and avoid a heart attack.”

Managers who want to visualize their reef’s health can observe the glow by using a blue flashlight and a yellow filter over their snorkel mask, or they can film the phenomenon with a camera equipped with these same features. If managers notice the initial drop in coral glow that indicates an impending problem, for example, immediate action could perhaps be taken to try and rescue the reef.

“So the idea is that we can use coral fluorescence as a early indicator of coral health prior to bleaching, which could actually give time for managers to do something if they wanted to take actions to protect the reef. Obviously that may be difficult on a large scale,” she explained, adding that “as reefs become degraded the few that we have left might be protected more aggressively.”

Further research on how these findings might apply to other species of coral is needed, the authors write. They also hope that future studies will combine biology with engineering to help design a digital imaging system that better captures and quantifies the extent to which corals change their glow.