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You may never have heard of Pteropods but they play a very important role in keeping the ocean's ecosystem in balance, because Pteropods make up a significant pat of the foundation for the food chain.


Climate change: Pacific Ocean acidity dissolving shells of key species

By Paul Rogers

In a troubling new discovery, scientists studying ocean waters off California, Oregon and Washington have found the first evidence that increasing acidity in the ocean is dissolving the shells of a key species of tiny sea creature at the base of the food chain.

The animals, a type of free-floating marine snail known as pteropods, are an important food source for salmon, herring, mackerel and other fish in the Pacific Ocean. Those fish are eaten not only by millions of people every year, but also by a wide variety of other sea creatures, from whales to dolphins to sea lions.

If the trend continues, climate change scientists say, it will imperil the ocean environment.

"These are alarm bells," said Nina Bednarsek, a scientist with the National Oceanic and Atmospheric Administration in Seattle who helped lead the research. "This study makes us understand that we have made an impact on the ocean environment to the extent where we can actually see the shells dissolving right now."

This isn't the first alarm to be sounded about acidic seawater threatening species that make up the base for the ocean's food chain.  

Last year scientists made similar warnings about a small but very important cold water species named Krill. The Krill eat algae that live on the bottom surface of sea ice and since the amount of sea ice is diminishing so is the feeding ground for Krill.    

Life in Antarctica Relies on Shrinking Supply of Krill

Less Ice Means Fewer Krill

Atkinson and his three co-authors had conducted the most comprehensive study yet of krill abundance and distribution in the Southern Ocean, gathering data from all the net samples they could find over the previous 80 years, a total of 12,000 summer net-hauls. This database showed that the southwest Atlantic sector of the Southern Ocean—the narrow, productive stretch between the Antarctic Peninsula and South Africa—contained more than half the krill in the Southern Ocean. It also indicated that krill stocks in this crucial sector had declined by 80 percent in the previous 30 years.

The study did not directly identify the cause of the decline, but it provided a hint: Summer krill densities in the southwest Atlantic correlate positively with sea-ice extent the previous winter.

Antarctic sea ice typically expands fivefold in the course of a year. At its winter maximum, it often covers eight million square miles, nearly twice the area of the Antarctic continent and eight percent of the entire Southern Hemisphere. This vast substrate of ice—or superstrate, actually, as it forms the frozen ceiling of the ocean—is colonized by ice algae, which green the brine channels in the ice and the undersides of drifting floes.

Krill, with rows of rakelike bristles at the tips of their thoracopods, scrape the algae from the ice and pass it on to their mandibles. The vast extent of these filmy krill pastures, their bioenergetic potential, and their crucial role in sustaining the Antarctic ecosystem through the winter months have only recently been incorporated in scientific models. This adjustment comes even as science has begun to quantify how rapidly, in response to climate change, the sea ice is diminishing at both poles, not only in extent but in duration.

"Krill are dependent on the sea ice in winter," Collins said. "The juvenile krill in particular feed under the sea ice, and some of the adult krill as well. Declines in sea ice associated with warming means less habitat for krill and, therefore, in the longer term, certainly less krill. I do think we're looking at that sort of thing potentially, in the middle to long term. I think Atkinson's work suggests that decline is already beginning to happen."

                                       
                                                            Krill

The ocean ecosystems are being altered by climate change threatening the collapse of the species that make the base of the food chain, raising the possibility that the oceans food chains will be disrupted in catastrophic ways. Millions of people depend on the roughly 160 million tons of fish caught this year worldwide.
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Also see: Oceans are Acidifying at the Fastest rate in 300,000,000 years. What Me Worry?

Originally posted to Lefty Coaster on Thu May 01, 2014 at 01:27 AM PDT.

Also republished by Climate Change SOS, Climate Hawks, and DK GreenRoots.

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