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By Marlene Cimons
There have been numerous wake-up calls about the effects of climate change on marine life. As ocean waters heat up, they are bleaching corals. Growing levels of carbon dioxide are acidifying seawater, which is degrading the shells and skeletons of sea organisms. The rising temperatures are prompting fish to migrate to colder waters, even causing them to shrink.
Now climate change is starting to affect their sense of smell, a phenomenon that will worsen in the coming years if global warming continues unabated, according to new research. A sense of smell is indispensable to fish. They use it to find food, detect imminent danger and elude predators, to find safe environments and spawning areas, even to recognize one another.
To lose it could threaten their very survival. If this happens, it also would mean big trouble for the fishing industry, tourism and, most importantly, global nutrition, since many of the world's people—including its poorest—depend on fish for food.
Fishermen in Vietnam.Pexels
"Future levels of carbon dioxide can have large negative effects on the sense of smell of fish, which can affect fish population numbers and entire ecosystems," said Cosima Porteus, a researcher at the University of Exeter and author of the study, which appears in the journal Nature Climate Change.
"This can be prevented, but we must reduce carbon emissions now before it's too late."
Carbon dioxide combines with seawater to produce carbonic acid, which makes the water more acidic. Since the Industrial Revolution, oceanic CO2 has risen by 43 percent and is projected to be two and a half times current levels by the end of this century, according to the scientists.
Experts believe that about half of anthropogenic carbon dioxide—that is, emissions produced by human activities, such as the burning of fossils fuels—has over time ended up in the oceans, lowering the pH of seawater, and making it more acidic.
Porteus—collaborating with scientists from the Centre of Marine Sciences in Faro, Portugal and the Centre for Environment, Fisheries and Aquaculture Science in the UK—compared the behavior of juvenile sea bass at carbon dioxide levels typical of today's ocean conditions with those predicted for the end of the century.
The sea bass used in the study.Cosima Porteus / Nature Climate Change
They found that sea bass exposed to the more acidic conditions swam less and were less likely to react when encountering the smell of a predator, offered to them in the form of very dilute monkfish bile. Also, they were more likely to "freeze," a sign of anxiety, she said.
"I found the longer they were in high CO2, the worse they fared," she said. The scientists also measured the ability of the fish to detect certain odors in different levels of acidity by recording their nervous system activity.
"I recorded the olfactory—smell—nerve response by measuring the electrical activity of the nerve to these different odorants in the water that flowed over the nose of the fish in both normal and high CO2 seawater," Porteus said.
"The odorants tested were those that would be involved in finding food—amino acids—and in recognizing fish of the same or other species, including bile acids, bile, intestinal fluid, etc., at different concentrations, and at levels they would encounter in the wild," she added.
The researchers found that seawater acidified with levels of carbon dioxide that are expected by the end of the century—if global warming continues—reduced the sense of smell of sea bass by half, compared with today's levels.
"Their ability to detect and respond to some odors associated with food and threatening situations was more strongly affected than for other odors," Porteus said. "We think this is explained by acidified water affecting how odorant molecules bind to olfactory receptors in the fish's nose, reducing how well they can distinguish these important stimuli."
They did not compare the impact of today's ocean acidity levels with those of pre-industrial times, although they plan further research to do so. "It is possible that sea bass are already being affected by a rise in oceanic pH," she said.
Fresh catch at the fish market.Pixabay
The researchers also studied the impact of high levels of CO2 and acidity on genes expressed in the nose and brain of sea bass and found them altered—but not in a good way. Rather than adjust, things deteriorated, Porteus said.
"The gene expression experiment was conducted to see if these fish were able to compensate for their loss of sense of smell over a short period of time, not generations," she explained. "Animals have some ability to respond to a stressful condition by making more proteins or different proteins that work better under different conditions."
Researchers can determine this by looking at what genes change or are different between animals exposed to different conditions, normal and high CO2, for example, according to Porteus.
"One way to smell something better is to have more receptors detecting these smells in order to increase the chance that particular smell will be detected, and therefore increase the expression of these receptors," she said. "Another way is [for them] to make a slightly different receptor that works better under lower pH. However, we did not find any evidence this was the case."
Instead, they found the fish were making fewer such receptors, making it more difficult for them to detect smells, she said.
"There was a decrease in 'active' genes, indicating that these cells were less excitable, therefore responding even less to smells in the environment," she said. "This means that these fish had a reduced sense of smell and instead of compensating for this problem, the changes in their cells were making the problem worse. This matched our observations of their behavior."
The team chose to study European sea bass because they are an economically important species, both for food consumption and for sport fishing, Porteus said.
Nevertheless, "we think the ability to smell odors is similar in most, if not all, fish species, so what we have found for sea bass will almost certainly apply to all fish species, and maybe invertebrates too, such as crabs, lobsters etc.," she said. "So all the commercially important species are likely to be affected in a similar way, such as salmon, cod, plaice, turbot, haddock etc."
This is important because 20 percent of the protein consumed by 3 billion people comes from seafood, and about 50 percent of this comes from fish caught from the wild, according to Porteus. "Therefore, increases in carbon dioxide in the ocean have the potential to affect all fish species, including those that many people rely on for food and livelihood," she said.
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Global Banks, Led by JPMorgan Chase, Invested $1.9 Trillion in Fossil Fuels Since Paris Climate Pact
By Sharon Kelly
A report published Wednesday names the banks that have played the biggest recent role in funding fossil fuel projects, finding that since 2016, immediately following the Paris agreement's adoption, 33 global banks have poured $1.9 trillion into financing climate-changing projects worldwide.
By Patti Lynn
2018 was a groundbreaking year in the public conversation about climate change. Last February, The New York Times reported that a record percentage of Americans now believe that climate change is caused by humans, and there was a 20 percentage point rise in "the number of Americans who say they worry 'a great deal' about climate change."
England faces an "existential threat" if it does not change how it manages its water, the head of the country's Environment Agency warned Tuesday.
By Jessica Corbett
A new analysis revealed Tuesday that over the past two decades heat records across the U.S. have been broken twice as often as cold ones—underscoring experts' warnings about the increasingly dangerous consequences of failing to dramatically curb planet-warming emissions.
By Madison Dapcevich
Ask any resident of San Francisco about the waterfront parrots, and they will surely tell you a story of red-faced conures squawking or dive-bombing between building peaks. Ask a team of researchers from the University of Georgia, however, and they will tell you of a mysterious string of neurological poisonings impacting the naturalized flock for decades.
The initial cause of the fire was not yet known, but it has been driven by the strong wind and jumped the North Santiam River, The Salem Statesman Journal reported. As of Tuesday night, it threatened around 35 homes and 30 buildings, and was 20 percent contained.
The unanimous verdict was announced Tuesday in San Francisco in the first federal case to be brought against Monsanto, now owned by Bayer, alleging that repeated use of the company's glyphosate-containing weedkiller caused the plaintiff's cancer. Seventy-year-old Edwin Hardeman of Santa Rosa, California said he used Roundup for almost 30 years on his properties before developing non-Hodgkin's lymphoma.
"Today's verdict reinforces what another jury found last year, and what scientists with the state of California and the World Health Organization have concluded: Glyphosate causes cancer in people," Environmental Working Group President Ken Cook said in a statement. "As similar lawsuits mount, the evidence will grow that Roundup is not safe, and that the company has tried to cover it up."
Judge Vince Chhabria has split Hardeman's trial into two phases. The first, decided Tuesday, focused exclusively on whether or not Roundup use caused the plaintiff's cancer. The second, to begin Wednesday, will assess if Bayer is liable for damages.
"We are disappointed with the jury's initial decision, but we continue to believe firmly that the science confirms glyphosate-based herbicides do not cause cancer," Bayer spokesman Dan Childs said in a statement reported by The Guardian. "We are confident the evidence in phase two will show that Monsanto's conduct has been appropriate and the company should not be liable for Mr. Hardeman's cancer."
Some legal experts said that Chhabria's decision to split the trial was beneficial to Bayer, Reuters reported. The company had complained that the jury in Johnson's case had been distracted by the lawyers' claims that Monsanto had sought to mislead scientists and the public about Roundup's safety.
However, a remark made by Chhabria during the trial and reported by The Guardian was blatantly critical of the company.
"Although the evidence that Roundup causes cancer is quite equivocal, there is strong evidence from which a jury could conclude that Monsanto does not particularly care whether its product is in fact giving people cancer, focusing instead on manipulating public opinion and undermining anyone who raises genuine and legitimate concerns about the issue," he said.
Many regulatory bodies, including the U.S. Environmental Protection Agency, have ruled that glyphosate is safe for humans, but the World Health Organization's International Agency for Research on Cancer found it was "probably carcinogenic to humans" in 2015. A university study earlier this year found that glyphosate use increased cancer risk by as much as 41 percent.
Hardeman's lawyers Jennifer Moore and Aimee Wagstaff said they would now reveal Monsanto's efforts to mislead the public about the safety of its product.
"Now we can focus on the evidence that Monsanto has not taken a responsible, objective approach to the safety of Roundup," they wrote in a statement reported by The Guardian.
Hardeman's case is considered a "bellwether" trial for the more than 760 glyphosate cases Chhabria is hearing. In total, there are around 11,200 such lawsuits pending in the U.S., according to Reuters.
University of Richmond law professor Carl Tobias told Reuters that Tuesday's decision showed that the verdict in Johnson's case was not "an aberration," and could possibly predict how future juries in the thousands of pending cases would respond.