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Current rate of ocean acidification not seen in 300 million years

November 19, 2017

New York City (Bernd F. Laeschke – December 2012): Oceans around the globe may be acidifying faster today than they did in the last 300 million years, a new study concludes. The decrease in pH is mainly caused by the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere.

"What we're doing today really stands out in the geologic record," says Bärbel Hönisch, a paleoceanographer at Columbia University's Lamont-Doherty Earth Observatory and lead author of the study. "We know that life during past ocean acidification events was not wiped out - new species evolved to replace those that died off. But if industrial carbon emissions continue at the current pace, we may lose organisms we care about - coral reefs, oysters, salmon."

Corresponding to the rising of carbon in the atmosphere there has been a rise of carbon going into the oceans that act like a sponge to draw down excess carbon dioxide from the air. The gas reacts with seawater to form carbonic acid, which over time is neutralized by fossil carbonate shells on the seafloor. If too much carbon dioxide enters the ocean too quickly, it can deplete the carbonate ions that corals, mollusks and some plankton need to build reefs and shells.

In a review of hundreds of paleoceanographic studies, the researchers found evidence for only one period in the last 300 million years when the oceans changed as fast as today: the Paleocene-Eocene Thermal Maximum, or PETM. In ocean sediment cores, the PETM appears as a brown mud layer flanked by thick deposits of white plankton fossils.

About 56 million years ago, a mysterious surge of carbon into the atmosphere warmed the planet and turned the oceans corrosive. In about 5,000 years, atmospheric carbon doubled to 1,800 parts per million (ppm), and average global temperatures rose by about 6 degrees Celsius. The carbonate plankton shells littering the seafloor dissolved, leaving the brown clay layer that scientists see in sediment cores today.

As many as half of all species of benthic foraminifera, a group of one-celled organisms that live at the ocean bottom, went extinct, suggesting that deep-sea organisms higher on the food chain may have also disappeared, said paper co-author Ellen Thomas, a paleoceanographer at Yale University. "It's really unusual that you lose more than 5 to 10 percent of species.”

Scientists estimate that ocean acidity may have fallen as much as 0.45 units as the planet vented stores of carbon into the air. "These scientists have synthesized and evaluated evidence far back in Earth's history," said Candace Major, program officer in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research. "The ocean acidification we're seeing today is unprecedented," said Major, "even when viewed through the lens of the past 300 million years, a result of the very fast rates at which we're changing the chemistry of the atmosphere and oceans."

In the last hundred years, rising carbon dioxide from human activities has lowered ocean pH by 0.1 units, an acidification rate at least 10 times faster than 56 million years ago, says Hönisch. The Intergovernmental Panel on Climate Change (IPCC) predicts that pH will fall another 0.2 units by 2100, raising the possibility that we may soon see ocean changes similar to those observed during the PETM.

The study finds two other analogs for modern day ocean acidification - the extinctions triggered by massive volcanism at the end of the Permian and Triassic eras, about 252 million and 201 million years ago, respectively. But the authors caution that because ocean sediments older than 180 million years have been recycled back into the deep Earth, scientists have fewer records to work with.

During the "Great Dying" at the end of the Permian, about 252 million years ago, about 96 percent of life disappeared. Massive eruptions from what is known as the Siberian Traps in present-day Russia are thought to have triggered earth's biggest extinction.

Over a period of 20,000 years or longer, carbon in the atmosphere rose dramatically. Scientists have found evidence for ocean dead zones, and preferential survival of organisms predisposed to carbonate-poor seawater and high blood-carbon levels, but so far they have been unable to reconstruct changes in ocean pH or carbonate.

At the end of the Triassic, about 201 million years ago, a second burst of mass volcanism associated with the break-up of the supercontinent Pangaea doubled atmospheric carbon and touched off another wave of die-offs. Coral reefs collapsed and an entire class of sea creatures, the eel-like conodonts, vanished. On land, large plant-eating animals gave rise to meat-eating dinosaurs like Tyrannosaurus rex as the Jurassic era began.

A greater extinction of tropical species has led some scientists to question whether global warming rather than ocean acidification was the main killer at this time. Scientists believe that the most notorious of all extinctions, the one that ended the Age of Dinosaurs with a falling asteroid 65 million years ago, may not have been associated with ocean acidification. The asteroid impact in present-day Mexico released toxic gases and possibly set off fires that sent surges of carbon into the air. Though many species of plankton went extinct, coral reefs and benthic foraminifera survived.

In lab experiments, scientists have tried to simulate modern ocean acidification, but the number of variables currently at play, including high carbon dioxide, warmer temperatures, reduced ocean pH and dissolved oxygen levels, make predictions difficult. An alternative to investigating the paleo-record has been to study natural carbon seeps from offshore volcanoes that are producing the acidification levels expected by the year 2100.

In a study of coral reefs off Papua New Guinea, scientists found that during long-term exposure to high carbon dioxide and pH 0.2 units lower than today or at a pH of 7.8 as predicted by the IPCC for 2100, reef biodiversity and regeneration suffered.

Squids: Scientists study sense of hearing

November 19, 2017

Woods Hole (Bernd F. Laeschke – November 2010): Ordinary squid may provide clues about the origin and evolution of the sense of hearing. Little is known about how well squid hear and whether they rely on hearing to navigate, sense danger, and communicate with each other. Scientists have now learned that the squid hearing system has some similarities and some differences compared to human hearing.

Squid have a pair of organs called statocysts, balance mechanisms at the base of the brain that contain a tiny grain of calcium, which maintains its position as the animal maneuvers in the water. Each organ is a hollow, fluid-filled sac lined with hair cells, like human cochlea. On the outside of the sac, the hair cells are connected to nerves, which lead to the brain. The calcium grain, called a statolith, enables the squid to sense its position in the water, based on which hair cells it touches at a given moment.

When a squid moves quickly as it does when it flees an approaching predator, the calcium stone lags behind slightly before catching up to the hair cells. “Kind of like your stomach on a roller coaster,” says T. Aran Mooney, a biologist at the Woods Hole Oceanographic Institution (WHOI). “The hair cells are very sensitive and can detect the calcium statolith lagging behind, then catching up.”

According to Mooney, who began his hearing research while working on his Ph.D. at the University of Hawaii, the squids hearing organs are structurally analogous to auditory system of humans. He believes that the organs are on its way to becoming an ear like the more familiar organs of vertebrates.

In a serious of experiments, the scientist did lower squids into a shallow, 3-foot-wide tank. Also in the tank is a speaker that can emit a broad range of sound frequencies - pure tones repeated about 1,000 times for each frequency. The responses were recorded and the preliminary findings indicate that the squid actually can hear. “But they only hear up to a certain frequency, about 500 Hz, which is pretty typical of a lot of fish that don’t hear very well,” Mooney says. “Humans hear from about 20-20,000 Hz. Squid also do not detect the very high frequency sounds of dolphin echolocation clicks.”

That may help explain why squid are such a prolific food source: They may not hear well enough to get out of the way of approaching predators. However, squids have another defense mechanism: when the researcher put them in a CT scanner, he noticed that squid have almost the same density as water. The CT could not image the squid body, illustrating that the species is nearly transparent to sound. This makes them very difficult for echo locating predators to detect.
“It’s been suggested that a primary evolutionary drive behind hearing is to locate where the sound source is,” Mooney said. “If there’s a predator coming you’d better darn well know where that predator is coming from so that you can get out of the way.”

He also thinks squid hearing organs can tell scientists a lot about how ears originated and evolved. “Humans, fish, and lots of animals use hair cells to detect sound and movement. Their hair cell structures are similar to squid, but also quite different. There is probably a basic structure which evolved millions of years ago, but vertebrates and invertebrates have taken quite different evolutionary paths since. By learning more about squid hearing and squid hair cells, we might learn what is important in human hearing and human hair cells, or other animals for that matter.”

Titanic: Expedition captures images and hi-def video

December 04, 2016

St. John’s (Bernd F. Laeschke – August 2010): During an expedition to the wreck of the Titanic, stunning 3-D images have been captured for the first time. Scientists and archaeologists aboard the research vessel The Jean Charcot produced the most detailed ever map of the wreck site. The RMS Titanic, Inc., the company that was awarded ownership rights to the wreckage as salvor-in-possession in 1994, organized the new expedition that is co-led by the Woods Hole Oceanographic Institution (WHOI).

A YouTube video-clip titled “Expedition Titanic: ROV Recovery” is available here.

RMS Titanic was the largest passenger steamship in the world when she set off on her maiden voyage from Southampton, England to New York City on 10 April 1912. The Olympic-class passenger liner, owned by the White Star Line, struck an iceberg at 11:40 pm on April 14, 1912 about 400 miles (644 kilometers) south of the Grand Banks of Newfoundland, and sank at 2:20 am the following morning. In one of the deadliest peacetime maritime disasters, 1,517 people drowned, and only 706 survived. The 882 feet (269 meter) vessel did have a displacement of 52,310 tons. With a height of 175 feet (53 meter), the Titanic featured 9 decks and 840 staterooms. Fully loaded, it could carry 2,687 passengers and a crew of 860.

Chris Davino, President of RMS Titanic, Inc., outlines the goals of the current Titanic expedition in this YouTube video here. The expedition was able to probe the wreck and the large debris field surrounding it with a pair of robots that captured thousands of photographs and hours of high definition video. Scientists aim to complete a full inventory of the ships remains and artifacts that are partially buried under almost a century of sediment.

Some of the most stunning images of the Titanic wreck are seen in this video, placed on YouTube by Premier Expeditions.

Hermit crabs congregate to find a larger snail shell

December 04, 2016

Berkeley (Bernd F. Laeschke – October 2012): Terrestrial hermit crabs congregate to kick another crab out of its shell and move into a larger home, research from a University of California, Berkeley finds. The decapod crustaceans (Coenobita compressus) usually live inside a discarded snail shell and forages for plants and carrion along the Pacific coast from Mexico to Peru. All hermit crabs appropriate abandoned snail shells for their homes, but the dozen or so species of land-based hermit crabs are the only ones that hollow out and remodel their shells, sometimes doubling the internal volume. This provides more room to grow, more room for eggs and a lighter home to lug around as they forage.

But empty snail shells are rare on land, so the best hope of moving to a new home is to kick others out of their remodeled shells, said Mark Laidre, a UC Berkeley Miller Post-Doctoral Fellow. When three or more terrestrial hermit crabs congregate, they quickly attract dozens of others eager to trade up. They typically form a conga line, smallest to largest, each holding onto the crab in front of it, and, once a hapless crab is wrenched from its shell, simultaneously move into larger shells.

“The one that gets yanked out of its shell is often left with the smallest shell, which it can’t really protect itself with,” said Laidre, who is in the Department of Integrative Biology. “Then it’s liable to be eaten by anything. For hermit crabs, it’s really their sociality that drives predation.”

The crabs’ unusual behavior is a rare example of how evolving to take advantage of a specialized niche - in this case, land versus ocean - led to an unexpected byproduct: socialization in a typically solitary animal.

“No matter how exactly the hermit tenants modify their shelters, they exemplify an important, if obvious, evolutionary truth: living things have been altering and remodeling their surroundings throughout the history of life,” wrote UC Davis evolutionary biologist Geerat J. Vermeij in a commentary in the journal Current Biology that first published the research. “Organisms are not just passive pawns subjected to the selective whims of enemies and allies, but active participants in creating and modifying their internal as well as their external conditions of life,” Vermeij concluded.

Laidre conducted his studies on the Pacific shore of Costa Rica, where the hermit crab Coenobita compressus can be found by the millions along tropical beaches. He tethered individual crabs, the largest about three inches long, to a post and monitored the free-for-all that typically appeared within 10-15 minutes.

Most of the 800 or so species of hermit crab live in the ocean where empty snail shells are common because of the prevalence of predators like shell-crushing crabs with wrench-like pincers, snail-eating puffer fish and stomatopods, which have the fastest and most destructive punch of any predator. On land, however, the only shells available come from marine snails tossed ashore by waves. Their rarity and the fact that few land predators can break open these shells to get at the hermit crab may have led the crabs to remodel the shells to make them lighter and more spacious.

The importance of remodeled shells became evident after an experiment in which Laidre pulled crabs from their homes and instead offered them newly vacated snail shells. None survived. Apparently, he said, only the smallest hermit crabs take advantage of new shells, since only the small hermit crabs can fit inside the unremodeled shells. Even if a crab can fit inside the shell, it still must expend time and energy to hollow it out, and this is something hermit crabs of all sizes would prefer to avoid if possible.

Pearse Resurgence: Cave divers discover three new species

December 04, 2016

New Zealand (Bernd F. Laeschke – June 2012): Cave divers discovered several new species - a transparent amphipod, a worm, and a small snail -in the Pearse Resurgence, a system in the remote Motueka Valley on the South island of New Zealand near Nelson. Pearse Resurgence is connected to the Nettlebed Cave, a deep, extensive cave system in the Mount Arthur Range. It was thought to be the deepest cave system in the southern hemisphere until divers pushed deeper in the nearby Ellis Basin cave system during an expedition in April 2010.

"It's not easy to get inside the caves, and we want to know about the very specific life in them," says Dr. Graham Fenwick, a scientist at New Zealand’s National Institute of Water and Atmospheric Research (NIWA). "It's important to do an inventory of life in New Zealand, and in this case, it's a pretty special type of environment, and we don't have many limestone karst systems that are readily explored."

Worldwide, these aquifer studies are yielding rich troves of biodiversity. The importance of the stygofauna is twofold - they contribute to the health of the aquifer by bio-filtration and in turn they may represent an important marker of the health of the water.

The bio-survey in the Pearse Resurgence was performed using two techniques. Firstly, any invertebrates observed free swimming in the cave were captured by hand using a tube with a bulb on the end. The second technique involved the deployment of baited fauna traps in the cave at depths from 16 to 377 feet (5 to 115 meters) below the surface. Small plastic jars baited with a small shrimp were filled with nylon gauze and secured in various places in the cave, in crevices and amongst sediments.

One species of amphipod crustacean new to science dominated the stygofauna collected from the Pearse Resurgence. This species is completely colorless. "It is 6-8mm long, the divers could see it crawling over rocks, it really is a beautiful animal. It belongs to the poorly known genus Paraleptamphopus, one of two genera within the New Zealand endemic Family Paraleptamphopidae," says Fenwick.

Originally described from Canterbury's deep alluvial aquifers, this family is represented by species inhabiting groundwater and marginally subterranean habitats throughout New Zealand. Within the Pearse Resurgence, this amphipod was found most commonly within the main shaft, where the expedition's divers stalked it on rock faces or caught it in small traps baited with shrimp.

It appears to live on the water-worn rock surfaces from within 6.56 feet (2 meters) of the surface of the main shaft's air bell, to depths of more than 131 feet (40 meters) where they were taken amongst gravel and finer sediments.

The two other stygofaunal invertebrates discovered in the system were a minute gastropod snail (about 0.06 inches or 1.5 millimeter in diameter) and an oligochaete worm (about 0.31 inches or 8 millimeter long). Both were taken from rare deposits of fine sandy sediments within the main shaft at depths from 49 to 112 feet (15-34 meters). "All these new finds are endemic to this area," says Fenwick.