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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.