November 26, 2013
Seahorses belong to the genus Hippocampus, which gets its name from the Greek words for “horse” and “sea monster.” With their extreme snouts, weirdly coiled bodies and sluggish movements produced by to two puny little fins, these oddly shaped fish seem like an example of evolution gone terribly awry. And yet, new research published today in Nature Communications shows that it is precisely the seahorse’s uncanny looks and slow motions that allow it to act as one of the most stealthy predators under the sea.
Seahorses, like their close relatives the pipefish and sea dragons, sustain themselves by feasting on elusive, spastic little crustaceans called copepods. To do this, they use a method called pivot feeding: they sneak up on a copepod and then rapidly strike before the animal can escape, much like a person wielding a bug swatter tries to do to take out an irritating but otherwise impossible-to-catch fly. But like that lumbering human, the seahorse will only be successful if it is able to get near enough to its prey to strike at very close range. In the water, however, this is an even greater feat than on land because creatures like copepods are extremely sensitive to any slight hydrodynamic change in the currents around them.
So how do those ungainly little guys manage to feed themselves? As it turns out, the seahorse is a more sophisticated predator than appearance might suggest. In fact, it is precisely its looks that make it an ace in the stealth department. To arrive at this surprising conclusion, researchers from the University of Texas at Austin and the University of Minnesota used holographic and particle image velocimetry–fancy ways of visualizing 3D movements and water flow, respectively–to monitor the hunting patterns of dwarf seahorses in the lab.
In dozens of trials, they found that 84 percent of the seahorses’ approaches successfully managed not to sound the copepod’s retreat alarms. The closer the seahorse could get to its unsuspecting prey and the faster it struck, the greater its odds of success, they observed. Once in range of the copepod, seahorses managed to capture those crustaceans 94 percent of the time. Here, you can see that method of attack, in which the seahorse’s giant head looks like a floating bit of marine sludge drifting toward the blissfully ignorant copepod:
The way the seahorse’s movements and morphology–especially its head–interact with the water particles, the researchers found, likely take the credit for its exceptional hunting skill. The animal’s arched neck acts like a spring for generating an explosive strike, they describe, while the shape of its snout–a thin tube with the mouth positioned at the very end–allows it to drift through the water while creating minimal disturbance.
To emphasize this pinnacle of engineering, the team compared water disruptions caused by seahorses with those of sticklebacks, a relative of the seahorse but with a more traditional fishy look. Thanks to the shape and contours of the seahorse’s head, that predator produced significantly less fluid deformation in the surrounding water than the stickleback. The poor stickleback possesses neither the morphology nor posture to generate “a hydrodynamically quiet zone where strikes occur,” the authors describe. In other words, while the seahorse may appear a bit odd so far as fishes go, evolution was obviously looking out for that funny but deadly animal’s best interests.
November 21, 2013
Over the course of 1700 miles, they sampled the water for small pieces of plastic more than 100 times. Every single time, they found a high concentration of tiny plastic particles. “It doesn’t look like a garbage dump. It looks like beautiful ocean,” Miriam Goldstein, the chief scientist of the vessel sent by Scripps Institution of Oceanography, said afterward. “But then when you put the nets in the water, you see all the little pieces.”
In the years since, a lot of public attention has been justifiably paid to the physical effects of this debris on animals’ bodies. Nearly all of the dead albatrosses sampled on Midway island, for instance, were found to have stomachs filled with plastic objects that likely killed them.
But surprisingly little attention has been paid to the more insidious chemical consequences of this plastic on food webs—including our own. “We’d look over the bow of the boat and try to count how many visible pieces of plastic were there, but eventually, we got to the point that there were so many pieces that we simply couldn’t count them,” says Chelsea Rochman, who was aboard the expedition’s Scripps vessel and is now a PhD student at San Diego State University. “And one time, I was standing there and thinking about how they’re small enough that many organisms can eat them, and the toxins in them, and at that point I suddenly got goosebumps and had to sit down.”
“This problem is completely different from how it’s portrayed,” she remembers thinking. “And, from my perspective, potentially much worse.”
In the years since, Rochman has shown how plastics can absorb dangerous water-borne toxins, such as industrial byproducts like PCB (a coolant) and PBDE (a flame retardant). Consequently, even plastics that contain no toxic substances themselves, such as polyethylene—the most widely used plastic, found in packaging and tons of other products—can serve as a medium for poisons to coalesce from the marine environment.
But what happens to these toxin-saturated plastics when they’re eaten by small fish? In a study published today in Scientific Reports, Rochman and colleagues fill in the picture, showing that the toxins readily transfer to small fish through plastics they ingest and cause liver stress.This is an unsettling development, given that we already know such pollutants concentrate further the more you move up the food chain, from these fish to the larger predatory fish that we eat on a regular basis.
In the study, researchers soaked small pellets of polyethylene in the waters of San Diego Bay for three months, then tested them and discovered that they’d absorbed toxins leached into the water from nearby industrial and military activities. Next, they put the pollution-soaked pellets in tanks (at concentrations lower than those found in the Great Pacific garbage patch) with a small, roughly one-inch-long species called Japanese rice fish. As a control, they also exposed some of the fish to virgin plastic pellets that hadn’t marinated in the Bay, and a third group of fish got no plastic in their tanks at all.
Researchers still aren’t sure why, but many small fish species will eat these sort of small plastic particles—perhaps because, when covered in bacteria, they resemble food, or perhaps because the fish simply aren’t very selective about what they put in their mouths. In either case, over the course of two months, the fish in the experiment consumed many plastic particles, and their health suffered as a result.
“We saw significantly greater concentrations of many toxic chemicals in the fish that were fed the plastic that had been in the ocean, compared to the fish that got either clean plastic or no plastic at all,” Rochman says. “So, is plastic a vector for these chemicals to transfer to fish or to our food chain? We’re now fairly confident that the answer is yes.”
These chemicals, of course, directly affected the fishes’ health. When the researchers examined the tiny creatures’ livers (which filter out toxins in the blood) they found that the animals exposed to the San Diego Bay-soaked plastic had significantly more indications of physiological stress: 74 percent showed severe depletion of glycogen, an energy store (compared to 46 percent of fish who’d eaten virgin plastic and zero percent of those not exposed to plastic), and 11 percent exhibited widespread death of individual liver cells. By contrast, the fish in the other treatments showed no widespread death of liver cells. One particular plastic-fed fish had even developed a liver tumor during the experimental period.
All this is bad news for the entire food webs that rest upon these small fish, which include us. “If these small fish are eating the plastic directly and getting exposed to these chemicals, and then a bigger fish comes up and eat five of them, they’re getting five times the dose, and then the next fish—say, a tuna—eats five of those and they have twenty-five times the dose,” Rochman explains. “This is called biomagnification, and it’s very well-known and well-understood.”
This is the same reason why the EPA advises people to limit their consumption of large predatory fish like tuna. Plastic pollution, whether found in high concentrations in the Great Pacific garbage patch or in the waters surrounding any coastal city, appears to be central to the problem, serving as a vehicle that carries toxins into the food chain in the first place.
October 31, 2013
Octopuses, those whip-smart but bizarre cephalopods, seem to embody everything creepy and mysterious about the sea–the thought of their soft squishy bodies lurking in the oceans’ dark reaches has inspired monsters ranging from the Kraken to the Caribbean Lusca. Their otherworldly forms, heightened by unfurling tentacles, find their way into more modern monsters and villains too–think Disney’s sea witch Ursula or Spider-Man’s Doc Oc. And don’t forget the octopus-themed horror movies!
A new book, Octopus! The Most Mysterious Creature in the Sea, by Katherine Harmon Courage, comes out today. Harmon Courage takes a deep dive into all things octopus, ranging from their culinary use in dishes around the world to their tragic sex lives. Here, we highlight a few of the fascinating points covered in the book.
1) Octopuses are waaay old. The oldest known octopus fossil belongs to an animal that lived some 296 million years ago, during the Carboniferous period. That specimen belongs to a species named Pohlsepia and is on display at the Field Museum in Chicago. Harmon Courage describes it as a “flattened cow patty” or a “globular splat,” but a close examination reveals the tell-tale eight arms and two eyes. Researchers aren’t sure, but possibly there’s an ink sack there, too. In other words, long before life on land had progressed beyond puny pre-dinosaur reptiles, octopuses had already established their shape for the millions of years to come.
2) Octopuses have three hearts. Two of the hearts work exclusively to move blood beyond the animal’s gills, while the third keeps circulation flowing for the organs. The organ heart actually stops beating when the octopus swims, explaining the species’ penchant for crawling rather than swimming, which exhausts them.
3) The plural of octopus is octopuses. The world “octopus” comes from the Greek, októpus, meaning “eight foot.” The word’s Greek roots means it’s pluralized as a Greek word, too, which depends on both a noun’s gender and the last letter it ends with. In this case, an -es is simply tacked on. So no octopi, octopodes or octopussies, Harmon Courage points out.
4) Aristotle thought octopuses were dumb. In his History of Animals, written in 350 BC, the Greek philosopher wrote that ”The octopus is a stupid creature, for it will approach a man’s hand if it be lowered in the water; but it is neat and thrifty in its habits: that is, it lays up stores in its nest, and, after eating up all that is eatable, it ejects the shells and sheaths of crabs and shell-fish, and the skeletons of little fishes.” After describing a few more quirks of octopus life history–it ejects ink for self-defense, it’s slimy, it can crawl on land–he flippantly signs off, “So much for the mollusca.” However, the big-brained cephalopod can navigate through mazes, solve problems and remember solutions, and take things apart for fun–they even have distinct personalities.
5) Octopus tentacles have a mind of their own. Two-thirds of an octopus’ neurons reside in its tentacles, not its head. As a result, the tentacles can problem solve how to open a shellfish while their owners are busy doing something else, like checking out a cave for more edible goodies. The tentacles can even react after they’ve been completely severed. In one experiment, severed tentacles jerked away in pain when researchers pinched them.
6) Octopus ink doesn’t just hide the animal. The ink also physically harms enemies. It contains a compound called tyrosinase, which, in humans, helps to control the production of the natural pigment melanin. But when sprayed in a predator’s eyes, tyrosinase causes a blinding irritation. It also garbles creatures’ sense of smell and taste. The defensive concoction is so potent, in fact, that octopuses that do not escape their own ink cloud can die.
7) Octopuses have blue blood. To survive in the deep ocean, octopuses evolved a copper rather than iron-based blood called hemocyanin, which turns its blood blue. This copper base is more efficient at transporting oxygen then hemoglobin when water temperature is very low and not much oxygen is around. But this system also causes them to be extremely sensitive to changes in acidity. If the surrounding water’s pH dips too low, octopuses can’t circulate enough oxygen. As such, researchers worry about what will happen to the animals as a result of climate change-induced ocean acidification.
8) Octopuses, to some, are erotic muses. Japan’s notorious “tentacle erotica” traces back to an 1814 woodblock print (potentially NSFW) titled Tako to Ama, or “Octopus and the Shell Diver.” According to Courage, the image takes inspiration from a legend about a female shell diver who is chased by sea creatures, included octopuses, after attracting the eye of a sea dragon god.
9) After mating, it’s game over for octopuses. Mating and parenthood are brief affairs for octopuses, who die shortly after. The species practices external fertilization. Multiple males either insert their spermatophores directly into a tubular funnel that the female uses to breathe, or else literally hand her the sperm, which she always accepts with one of her right tentacles (researchers do not know why). Afterwards, males wander off to die. As for the females, they can lay up to 400,000 eggs, which they obsessively guard and tend to. Prioritizing their motherly duties, females stop eating. But she doesn’t starve to death–rather, when the eggs hatch, the female’s body turns on her. Her body undertakes a cascade of cellular suicide, starting from the optic glands and rippling outward through her tissues and organs until she dies.
10) Most octopus for human consumption comes from North and West Africa. Octopus has been a popular food item in East Asia, Spain, Greece and other countries for centuries, and recently, it has gained popularity in the U.S. and beyond. Today, Koreans consume the most octopus. But that popularity has had an impact on octopus stocks in oceans around the world. In Japan, for example, octopus catches plummeted by 50 percent between the 1960s and the 1980s. The international demand for octopus inspired North and West African fisheries to start targeting the animals in the 80s, although recently demand has taken a toll on those waters as well, shifting fisheries from Morocco to Mauritania and, more recently, Senegal. According to the U.N. Food and Agriculture Organization, around 270,000 tons of octopus is imported by various countries around the world each year.
October 16, 2013
We often hear about melting sea ice, rising tides and bleached coral reefs, but climate change is poised to reverberate through a broader swath of the marine environment than these headline issues alone might suggest.
According to a new study published in PLoS Biology, “the entire world’s ocean surface will be simultaneously impacted by varying intensities of ocean warming, acidification, oxygen depletion, or shortfalls in productivity.” As the ocean’s biogeochemistry shifts, the paper reports, so too will its habitats and the creatures living there. This could mean hardship for some 470 to 870 million people–many of whom live in poverty–who depend upon the bounty of the sea to support livelihoods and fill dinner plates. And these impacts are not predicted to occur centuries down the road, either: according to the study, they may transpire as soon as 2100.
Nearly 30 scientists from around the world–including climate modelers, ecologists, biogeochemists and social scientists–co-authored the study. They built upon computer models from the Intergovernmental Panel for Climate Change by compiling data from 31 Earth System Models that included at least one ocean parameter. All told, 27,000 years’ worth of data of the various overlapping, aggregated variables were compiled into their new model.
With those data compiled, they then modeled two different future scenarios: one in which atmospheric carbon dioxide concentrations increase to 550 parts per million, and another in which they hit 900 ppm (the planet currently stands at about 400 ppm, as compared to pre-industrial times, when that measurement was 280 ppm). The former model represents values predicted if mitigation efforts are undertaken, while the latter is predicted for a “business-as-usual” scenario where we maintain current levels of greenhouse gas emissions into the future.
Their model predicted changes in temperature, oxygen levels, increased acidity and productivity (the creation of organic compounds by primary producers like phytoplankton) on both the ocean surface and the sea floor under those two future scenarios. Nearly across the board on the ocean’s surface, they found, their models predicted a continued warming and rise in acidity accompanied by a decline in oxygen and productivity. The only exception was in a small fraction of the sea in polar regions, where the sea surface would experience increased oxygen and productivity. The magnitude of these predicted changes, they write, will be greater than any comparable shifts over the past 20 million years.
“When you look at the world ocean, there are few places that will be free of changes; most will suffer the simultaneous effects of warming, acidification, and reductions in oxygen and productivity,” Camilo Mora, a geographer at the University of Hawaii at Mānoa, said in a press release.
The most drastic impacts, they found, will occur on the ocean’s surface, but the seafloor will also experience its share of smaller but still significant changes. Seafloor temperature and acidity will change only slightly compared to the surface, but there will be large reductions in the influx of carbon, which provides food for many bottom-dwelling organisms. The drop in dissolved oxygen on the sea floor will be similar to that experienced on the surface.
These changes may be enough to disrupt the ocean floor’s delicate ecosystem. ”Because many deep-sea ecosystems are so stable, even small changes in temperature, oxygen, and acidity may lower the resilience of deep-sea communities,” Lisa Levin, an oceanographer at the University of California, San Diego, and co-author of the paper, said in the release. “This is a growing concern as humans extract more resources and create more disturbances in the deep ocean.”
As for the surface, the magnitude of the projected changes will vary by place. The tropics will experience the smallest changes in acidity; temperate regions will suffer the least significant shifts in temperature and productivity; and the Southern Ocean near Antarctica will be spared the least fluctuations in oxygen. But overall, across the board the ocean surface will suffer significant impacts.
With those data in hand, they then overlaid habitat and biodiversity hot spot information for 32 diverse marine environments around the world to see how these changes would impact ocean flora and fauna. Coral reefs, seagrass beds and other shallow areas will suffer the greatest impacts, they found, while deep ocean seamounts and vents will suffer the least.
Humans will not be spared the repercussions of those changes. In a final analysis, they quantified humanity’s dependence on the ocean by analyzing global jobs, revenues and food that comes from the sea. Most of the up to 870 million people who will be affected most by these changes live in some of the world’s poorest nations, they found.
While these predictions are subject to the same limitations that plague any computer model that attempts to represent a complex natural system and project its future fate, the authors believe that the results are robust enough to strongly support the likelihood that our oceans will be very different places in the not-too-distant future. If carbon dioxide levels continue to rise, they write, “substantial degradation of marine ecosystems and associated human hardships are very likely to occur.”
“It is truly scary to consider how vast these impacts will be,” co-author Andrew Sweetman of the International Research Institute of Stavanger, Norway, emphasized in the press release. “This is one legacy that we as humans should not be allowed to ignore.”
September 25, 2013
Sure, it’s not much to look at. But stare long enough, and you’ll see a jaw (jutting out towards the right), a pair of nostrils (small perforations directly above the mouth cavity) and even a tiny eye socket (just above the mouth, to the left of the nostrils, staring out sideways).
This admittedly homely fish fossil, the 419-million-year old Entelognathus primordialis, was recently discovered in China and described for the first time in an article published today in Nature. What makes it remarkable is everything that’s come after it: It’s the oldest known creature with a face, and may have given rise to virtually all the faces that have followed in the hundreds of millions of years since, including our own.
The uncommonly well-preserved, three-dimensional fossil, analyzed by a group of researchers from the Chinese Academy of Sciences, was excavated near Xiaoxiang Reservoir in Southeast China, in a layer of sediment that dates to the Silurian period, which ranged from roughly 419 to 443 million years ago. All other fish specimens from this era are jawless fish (a group of more primitive creatures that still live on today as lampreys and hagfish), so this is the first one that has what we might call a face: a mouth, nose and two eyes.
It’s difficult to conclude very much about the behavior or lifestyle of the ancient creature, but we do know that it swam in water (land animals didn’t begin to evolve until the Devonian period, which spanned 359 to 419 million years ago) and was likely a top-level predator of the early ocean ecosystem.
What has scientists so excited, though, is that the particular anatomical features of this fossil could upend our understanding of how vertebrates evolved over time. “When I first saw this, I was completely blown away,” says Matt Friedman a paleobiologist at the University of Oxford that reviewed the paper and wrote an accompanying article in Nature. “It’s the kind of fossil you might see once or twice in your lifetime, as a research scientist.”
Friedman and others find the fossil so remarkable because it combines a series of characteristics from two different groups: placoderms, an ancient class of armored fish that went extinct millions of years ago, and bony fish, a lineage that gave rise to all modern fish with jaws and bone skeletons. Previously, it was assumed that placoderms died out completely (and that the other, more recent types of fish with similar armor plating had independently re-evolved it much later), while a different, shark-like group of fish called acanthodians led to the bony fishes.
“What a fossil like this shows is that maybe that’s not the case,” Friedman says. “Because if you look at just the top of the skull and the body, it looks like a placoderm. But when you look at the side, and the front, you see it has jaws that, bone for bone, closely resemble the jaws of bony fish.”
This is significant because of what happened next: bony fish gave rise to all modern vertebrate fish, along with all amphibians, reptiles, birds and mammals, including ourselves. In other words, this fossil might mean that the placoderms didn’t go extinct, but rather evolved into the tremendous diversity of animals that live on both land and sea—and that this ancient, strange-looking face belongs to one of your oldest ancestors.
Scientists won’t immediately jump to reorganize their evolutionary family trees overnight, but the new finding will prompt a period of renewed scrutiny of the previous model. “It’s going to take a while for people to digest it and figure out what it all means,” Friedman says. “From a fossil like this, you’ve got a cascade of implications, and this is just the first paper to deal with them.”
Eventually, though, this finding could help transform our understanding of just how evolution occurred in our planet’s ancient oceans—and how the primitive creatures that swam in them eventually gave rise to the faces we see everyday.