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mercoledì 13 gennaio 2016

Mass Mortality Events





On the chilly shores of Alaska’s Prince William Sound, tens of thousands of battered bird carcasses are washing up. The birds, all members of a species known as the common murre, appear to have starved to death, wildlife officials said Tuesday. Their black and white bodies lie strewn across the slick rock, or else bob in the shallow waters nearby.

Seven thousand miles away, on a sandy beach in southern India, more than 100 whales were discovered mysteriously stranded on shore this week. Already at least 45 of them are dead, according to the BBC, dried out and overheated by exposure to the sun. More may soon die if they can’t be safely returned to the ocean. The area hasn’t seen this big a stranding in more than 40 years.
These are two isolated incidents, but they’re not unlike others that have been reported in the past year — unexplained die-offs, abnormally large strandings, a worldwide coral bleaching bigger than almost anything else on record. Around the world, animal populations are vulnerable. Huge groups might be killed in a matter of days or weeks. In Kazakhstan in May of last year, more half of the world’s entire population of saiga antelope vanished in less than a month.

Incidents like these are often mysteries to be unraveled, with scientists sorting through various explanations — hunger, habitat loss, disease, disorientation — for the mass deaths. But in a swath of recent cases, many of the die-offs boil down to a common problem: the animals’ environments are changing, and they’re struggling to keep up.
Take the murres dying in Alaska. The seabirds are washing ashore with empty stomachs, Robb Kaler, a seabird biologist with the U.S. Fish and Wildlife Service in Anchoragetold The Washington Post Tuesday. It’s likely that they’re having trouble finding their normal food source — herring and other small fish — because of the region’s recent unusual weather and the abnormally high temperature of water in the sound.
Though large murre die-offs have happened before, this one is on a scale most experts have never seen before, former Fish and Wildlife Service biologist David Irons told KTVA-TV.

“Seabird biologists say seabirds are indicators of the health of the ecosystem,” he said. “Now they’re dying, and that is telling us something.”
Bad weather and warm waters are also thought to be the culprit behind the global coral bleaching event that scientists say is going on right now. Though coral looks like simply a colorful rock, it actually comprises many millions of tiny tentacled creatures living in a symbiotic relationship with brightly-colored algae, which give the corals both their color and their nutrients. When water temperatures rise — as they have this year, researchers say, due to a combination of climate change, a powerful El Nino and the Pacific’s weird warm “blob” — the corals become stressed and expel their algae partners, losing their vibrancy and the source of nutrients they need to survive. The ghostly white structures that remains are still alive, but they’re weakened, and the reef will lose much of its biodiversity until the algae can return. If they don’t, the corals are likely to die.

This is a bleaching, and the world’s reefs are in the midst of only the third global bleaching event in recorded history.

Far from any ocean, on the arid shrubgrass steppe of central Kazakhstan, more than 200,000 corpses of the endangered saiga antelope species were discovered scattered across the grassland last May. According to Scientific American, 70 percent of the world’s saigas —  strange, Dr. Seuss-looking creatures with spindly legs and a huge protruding snout — were killed in a matter of weeks. And no one knew why.
In November, researchers in Uzbekistan presented their best guess: an abnormally wet spring induced by climate change transformed some normally harmless pathogens that ordinarily live in the saigas’ guts. The suddenly lethal pathogens swept through Kazakhstan’s herds. Once sickened, the animals died in a matter of hours.

“This is really not biologically normal,” Richard A. Kock, of the Royal Veterinary College in London, told the New York Times last year. “I’ve worked in wildlife disease all my life, and I thought I’d seen some pretty grim things. But this takes the biscuit.”
Back in the U.S., the Los Angeles Times reported last August that the drought that has plagued western states for four years was causing a major die-off of vital fish populations like salmon, steelhead and the endangered delta smelt.Water levels were too low, and what’s more, water temperatures were too warm for fish and their offspring to survive.
The smelt numbers had diminished to “the last of the last,” UC Davis professor emeritus Peter Moyle, a leading authority on California’s native fish, told the LA Times. “It would be a major extinction event.”

And last July, researchers reported that global warming is working to “crush bumblebees in a kind of climate vice,” according to Nature.

“Bumblebee species across Europe and North America are declining at continental scales,” Jeremy Kerr, a biodiversity researcher at the University of Ottawa in Canada, told the scientific journal. “Our data suggest that climate change plays a leading, or perhaps the leading, role in this trend.”
It’s not only animals that are at risk. Researchers believe that the western drought killed 12 million trees in California’s forests, and estimated 58 million are so dry they’ve reached the brink of death, according to the San Francisco Chronicle. A study released that last month predicted that climate change would cause massive die-offs of the American southwest’s coniferous trees, like junipers and pinon pines, within the next half century.
Not every die-off of the past year can be blamed on climate change. Two “unusual mortality events” involving endangered Guadelupe fur seals — which were being stranded at eight times the normal rate on California’s central coast — and large whales in Alaska — where scientists have found the decomposing carcasses of more than 30 unlucky animals — have been loosely linked to that weird warm “blob” out in the Pacific. And the causes of other incidents — the recent whale stranding in India, for example — remain undetermined. Typically mass strandings are linked to toxic algae blooms, disease and trauma, and changes to the animals’ habitat, marine mammal expert Darlene Ketten told Scientific American in 2009.
In many ways, die-offs are an inevitable aspect of life on Earth. The ebb and flow of species’ success is part of the background noise of existence that drives evolution. Populations have risen and declined long before humans existed. They’re likely to continue to do so long after we’re gone.
But a study published in the Proceedings of the National Academy of Sciences last year suggests that the number of animal die-offs has gotten worse in recent years. And the researchers weren’t talking about small scale problems like the murres deaths or even the saiga die-offs either. They looked at more than 700 mass mortality events in which either 90 percent of the species was wiped out, more than a billion individuals were killed or 700 million tons (nearly 2,000 Empire State Buildings) worth of biomatter was destroyed.

What they found was not heartening. Mass Mortality Events (MMEs) are “rarely placed in a broader context,” the study’s authors reported. But they seem to be happening at an increased rate for birds, marine invertebrates and fish since the 1940s — even when researchers took into account that such events are more likely to be reported now than they were 75 years ago.
These die-offs matter not just because of the inherent value of the creatures involved, the authors said, but because whole ecosystems may depend on that species to survive.
MMEs, they wrote, “can reshape the ecological and evolutionary trajectories of life on Earth.”
Sarah Kaplan is a reporter for Morning Mix.

In pitiful animal die-offs across the globe — from antelopes to bees to seabirds — climate change may be culprit Sarah Kaplan January 13 2016



Where Have All the Animals Gone? 29 DICEMBRE 2015






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