When you’re nature’s ideal killing machine, perhaps color vision is merely an unnecessary affection. New research argues that sharks could be completely colorblind.
An Australian team led by Nathan Scott Hart investigated 17 shark species, peeking at the structure of their rod and cone photoreceptor cells in the retina. Human eyes come with red, green, and blue cone variations, allowing us to see in color. But not shark eyes. They appear to have just one kind of cone.
“Our study shows that contrast against the background, rather than color per se, may be more important for object detection by sharks,” Hart said. [CNN]
That, Hart says, may explain the common wisdom that sharks love yellow (and therefore you ought to avoid sunny swimsuits). It may be the reflective quality of yellow that catches a shark’s eye, not the hue itself.
“Bright yellow is supposed to be attractive to some sharks, presumably because it appears to the sharks as a very bright target against the water,” said Dr Hart. “So perhaps it is best to avoid those fluoro-yellow shorts next time you are in the surf.” [BBC News]
Oil wasn’t the only thing seeping into the Gulf of Mexico after the Deepwater Horizon disaster. The explosion of BP’s oil rig also triggered a leak a methane.
With the well unsealed, substantial amounts of the gas were released into the gulf. This plume of dissolved methane should have lurked in the water for years, hanging around like a massive planetary fart. But by August, it had disappeared. On three separate trips through the gulf, John Kessler from Texas A&M University couldn’t find any traces of the gas above background levels. He thinks he knows why – the methane was eaten by bacteria.
The gas pouring out of the broken well spurred the growth of bacteria called methanotrophs, which can break down methane as their only source of energy. They made short work of the gas. By the time that Kessler reached the gulf, just four months after the initial blowout, he found plenty of bacteria and precious little methane.
Check out the rest of Ed’s post on this discovery at Not Exactly Rocket Science.
As for BP itself: The petroleum giant now finds itself in the legal arena, but the company may avoid a worst-case scenario there. A presidential commission established to investigate the affair has found the brunt of liability to be BP’s, but also found the root cause of the disaster to be widespread, systematic mismanagement by everyone, and not rogue behavior by any one player. That is, BP will skate without being charged with “gross negligence” because everybody else made mistakes, too.
Commission co-chair William K Reilly said: “So a key question posed from the outset by this tragedy is, do we have a single company, BP, that blundered with fatal consequences, or a more pervasive problem of a complacent industry? Given the documented failings of both Transocean and Halliburton, both of which serve the offshore industry in virtually every ocean, I reluctantly conclude we have a system-wide problem.” [The Guardian]
80beats: Massive Coral Die-Off Found Just 7 Miles from BP Oil Spill Site
80beats: BP’s Oil Well of Doom Is Declared Officially, Permanently Dead
80beats: BP Report on Gulf Disaster Spreads the Blame Around
80beats: Scientists Find 22-Mile-Long Oily Plume Drifting in the Gulf of Mexico
80beats: Gulf Coast Turtle News: No More Fiery Death; Relocating 70,000 Eggs
Image: U.S. Coast Guard
About 540 million years ago, things were looking pretty rosy for complex life on Earth. Conditions were favorable, and the diversity of multicellular organisms took off during the so-called Cambrian Explosion. Trilobites frolicked. Brachiopods abounded. And then, things went south.
Between 490 million and 520 million years ago, a swift extinction event wiped out many of the Cambrian lifeforms. Geologists Benjamin Gill and Graham Shields-Zhou thinks they have found the trigger right in the midst of that era. According to their study in this week’s Nature, the ocean’s oxygen level plunged and the sulfur levels rose sharply 499 million years ago, killing off species that could not quickly adapt. That included some, but not all, of the trilobites that ruled the seas of the time.
Gill’s team decided to look at a specific subset of Cambrian extinctions that began 499 million years ago and lasted for 2 million to 4 million years. Other researchers had proposed that low oxygen levels — a condition known as anoxia — could be involved. But no one had marshaled enough evidence to prove that. [Science News]
The key to showing it in this case is in the chemical compositions of the samples the team collected, which hold clues to the ocean conditions of the time.
Gill and his colleagues took samples of 500-million-year-old rock from six locations around the world and measured the amounts of various isotopes of carbon and sulphur. Both were significantly different from the norm, suggesting that enormous amounts of carbon and sulphur were being buried. In modern oceans, this only occurs in low-oxygen waters like the Black Sea. [New Scientist]
The next question is, what drove down the oxygen levels so quickly? To that, Gill doesn’t have an answer. But such cyclical dramatic changes driving extinction is the rule, not the exception—there were several events during the latter Cambrian when many species were wiped out, and anoxia could have been at play in some of those, too.
DISCOVER: Just One Bite And Life Took Off
80beats: Ancient Rocks Show Oxygen Was Abundant Long Before Complex Life Arose
80beats: How “Snowball Earth” Could Have Triggered the Rise of Life
80beats: One of the Earth’s Earliest Animals Left Behind “Chemical Fossils”
Image: Wikimedia Commons
Leatherback turtles are the wandering type, undertaking far-flung ocean migrations of thousands of miles. What scientists who follow these long-lived creatures didn’t know, though, was just how many different routes they travel, and how far they journey before returning home. These are critical pieces of information for protecting the turtles, whose numbers are dropping. So Matthew Witt says he and his international team affixed trackers to the turtles and revealed the routes of their great sea voyages:
“What we’ve shown is that there are three clear migration routes as they head back to feeding grounds after breeding in Gabon, although the numbers adopting each strategy varied each year. We don’t know what influences that choice yet, but we do know these are truly remarkable journeys.” [The Guardian]
Gabon, in West Africa, is the home base for this largest breeding group of leatherbacks—it’s where they nest and lay their eggs. Witt’s team tracked 25 female turtles, all of whom followed one of those three general routes: out to the middle of the Atlantic and then back, down the African coast to the temperate South, or even all the way across the ocean to South America.
One female was tracked making a 7,563 kilometer (4,699 mile) journey traveling in a straight line across the South Atlantic from Africa to South America, said [Witt]. At a pace of 50 kilometers a day, that trip took about 150 days of consistent swimming, he said. [AP]
Some of the consequences of ocean acidification appear obvious: The shells of mollusks, for instance, could dissolve as the pH of ocean water drops thanks to the ocean pulling out some of the excess carbon dioxide humans put into the atmosphere. But what about more subtle effects of seawater growing more acidic?
In the Proceedings of the National Academy of Sciences this week, researchers set up an experiment to see whether the growing acidity of the ocean could disrupt the marine cycle of nitrogen, which provides key nutrients for plant life. Indeed it can, J. Michael Beman’s team found, and that’s another potentially dangerous side effect of the ocean as a carbon sink.
The authors of the study examined a specific step in the marine nitrogen cycle, called nitrification, in which microorganisms convert one form of nitrogen, ammonium, into nitrate, a form plants and other marine microorganisms require to survive. Previous research studies on experimentally acidified freshwater … in the laboratory have suggested that reduced pH slows nitrification, and one study in coastal ocean waters showed that large pH decreases did the same. [Scientific American]
So Beman sought to test the ocean by gathering samples of seawater from locations around the world and adding CO2 to simulate what will be happening to the oceans in the coming decades. Just decreasing the pH from 8.1 to 8.0 resulted in about 20 percent less nitrate creation, the team wrote. In their experiments that lowered pH between .05 and .14, the nitrate production dropped between 8 and 38 percent.
New sea creatures, humongous stars, and cockroach antibiotics: Those are just a few reader favorites from this year in science. As 2010 comes to a close, we bring you a dozen of the most popular 80beats posts of the year.
For more great stories from the year in science, check out DISCOVER’s Top 100 Stories of the Year.
The wild pink salmon of western Canada are in trouble: In the early 2000s, their numbers in some locations swiftly dropped by 90 percent or more. One explanation put forth for this steep population decline is that sea lice, parasites ubiquitous on farmed salmon, jumped to the wild variety of the fish. But this week in the Proceedings of the National Academy of Sciences, a new study casts doubt on that idea and says the sea lice are not to blame.
When Gary Marty of the University of California, Davis, and his colleagues looked at that aspect for the Broughton Archipelago of western Canada, they found that salmon survival was not lower in years when the juveniles passed by louse-infested farms. This, they say, suggests that something other than sea lice must be reducing survival rates. [New Scientist]
Marty’s team checked up on a decade worth of data dating back to before the 2002 crash, and found a few interesting things. First, they say, the predominance of the lice in wild populations appears to predict the number found in farms a little later, suggesting the parasites travel from wild salmon to farmed ones and not the other way around. Second, they argue, it does appear that a high number of lice in the farmed fish predicts higher than normal exposure for the juveniles of the wild variety, but that increased exposure can’t account for the huge population drop in the wild salmon.
It takes a tremendous amount of energy to move the largest animal on Earth from a standstill to chasing food in a fierce dive. Could the krill that a blue whale catches in its gargantuan mouth really provide a high enough calorie count to make all this effort worthwhile? To find out, Jeremy Goldbogen tagged whales with data recorders and monitored hundreds of their dives. It can take 770 to 1900 calories to get the whale moving, but it’s worth it.
When Goldbogen plugged the data from his recorders into a simulation of a feeding whale, he found that the lunge is staggeringly efficient. Despite the massive outlay in energy, the whale easily recoups anywhere from 6 to 240 times that amount, depending on how big it is and how tightly packed its krill targets are.
If a big whale attacks a particularly dense swarm, it can swallow up to 500 kilograms of krill, eating 457,000 calories in a single monster mouthful and getting back almost 200 times the amount it burned in the attempt. A smaller whale lunging at a sparse collection of krill would only get around 8,000 calories, but that’s still 8 times more than what it burned. Even when Goldbogen accounted for the energy needed to dive in search of prey, the whales still regained 3 to 90 times as much energy as they spent.
Not Exactly Rocket Science: Across an ocean, round a continent – the epic 10,000km voyage of a humpback whale
Not Exactly Rocket Science: Behold Livyatan: the sperm whale that killed other whales
80beats: Climate Scientists Enlist Narwhals to Study the Arctic Ocean
Image: Wikimedia Commons
The name Titanic means so many things: the gigantic, disastrous ship; a record-breaking and award-winning movie; and now, a new iron-eating bacterium found in the boat’s underwater grave. Says maritime historian Dan Conlin:
“What is fascinating to me is that we tend to have this idea that these wrecks are time capsules frozen in time, when in fact there [are] all kinds of complex ecosystems feeding off them, even at the bottom of that great dark ocean.” [Our Amazing Planet]
The new species of bacteria, named Halomonas titanicae, is described in this month’s International Journal of Systematic and Evolutionary Biology. The bacteria is slowing eating away at the 50,000 tons of iron in the wreck, which has been under the ocean for 98 years. H. titanicae appears to digest iron and turns it into knobs of corrosion products.
The movie was called Jaws for a reason. The great white shark’s powerful chompers make it a feared marine killing machine. However, researchers have found, it takes a while to grow into that ferociousness—adolescent great whites don’t yet have strong enough jaws to complete an attack on tougher prey without harming themselves, and it takes until adulthood for that jaw strength to develop.
The study by Toni Ferrara and colleagues, forthcoming in the Journal of Biomechanics, used the scanning technique called computerised tomography (CT) to take a look at the great white’s developing jaw, and compare it to a relative: the sand tiger shark (also called the grey nurse shark).
With these scans, they were able to create digital three-dimensional models of the sharks’ heads. The models revealed that the great white’s jaws are reinforced by layers of tough “mineralised cartilage”, which take years form. So until the sharks grow to approximately 3m [10 feet] long, they are unable to gouge chunks out of larger, tougher prey, such as sea mammals. [BBC News]