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Starfish Baby Boom Gives Hope Amid Wasting Disease

For the past two years, a wasting disease has devastated starfish along the West Coast, but a record number of babies is giving cause for optimism.

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For the past two years, a mysterious wasting disease has devastated starfish living along the West Coast, turning countless individual animals into goo. But now, a record number of surviving starfish babies is giving some researchers reason for cautious optimism.

The Oregon coast currently has a thriving community of juvenile starfish (or sea stars), with some places seeing populations with as many as 300 times the typical number, researchers said. That's welcome news, as up to 90 percent of sea stars in Oregon showed signs of the deadly wasting disease from June to August 2014, reports a new study published May 4 in the journal PLOS ONE.

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The high starfish numbers don't mean the deadly disease is gone, however, the researchers said. Another round of the wasting illness could kill the juvenile sea stars, including the purple ochre (Pisaster ochraceus), known as a "keystone" species because of its influence on the marine ecosystem, the researchers said. [In Photos: Sick Sea Stars Turn to Goo]

"When we looked at the settlement of the larval sea stars on rocks in 2014 during the epidemic, it was the same or maybe even a bit lower than previous years," study lead author Bruce Menge, a professor of marine biology at Oregon State University, said in a statement. "But a few months later, the number of juveniles was off the charts - higher than we'd ever seen."

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The juvenile starfish aren't the result of elevated starfish births or a massive re-settlement. Rather, these particular sea stars "just had an extraordinary survival rate into the juvenile stage," Menge said. The big question is "whether they can make it into adulthood and replenish the population without succumbing to sea star wasting disease," he said.

Perhaps this generation had a high survival rate because there was more food available, the researchers said. After the wasting disease killed off the majority of adult starfish, the young sea stars would have had more mussels and barnacles to eat, the scientists said.

The wasting disease left innumerable starfish with twisted arms that eventually disintegrated into slimy ooze. The epidemic spanned from Alaska to Baja California and also sickened sea stars on the East Coast.

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But it's anyone's guess what causes the disease, scientists said. Some attribute it to sea star-associated densovirus, and others said warmer waters triggered the disease's spread. But the new study found no association between water temperatures and the epidemic in Oregon, Menge said.

"The sea temperatures were warmer when the outbreak first began," he said. "But Oregon wasn't affected as early as other parts of the West Coast, and the outbreak reached its peak here when the sea temperature plummeted and was actually cooler than normal."

Interestingly, researchers at Cornell University in New York found evidence of densovirus in sea stars, the water column and marine sediments. The virus occurs naturally, but may become harmful to starfish experiencing stress, the researchers said.

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"Something triggered that virulence, and it happened on a coast-wide basis," Menge said. "Ocean acidification is one possibility, and we're looking at that now. Ultimately, the cause seems likely to be multifaceted." [Marine Marvels: Spectacular Photos of Sea Creatures]

Several clues provide hints about the disease. Sea stars that were continuously underwater, including those in tide pools, were more likely to die than were sea stars living on rocks that were usually above water, the researchers found.

Also, adult starfish were more likely to die than juveniles, probably because the older individuals had been exposed to the wasting disease for a longer period of time, the researchers said.

Menge and his colleagues have studied sea star habitats for more than 30 years. The loss of these creatures has already thrown the ecosystem out of whack, the researchers said. For instance, during the past two years, there has been a population boom in gooseneck barnacles, likely because adult sea stars weren't there to prey on them, the researchers said.

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As the tide rolls out, the ochre sea star (Pisaster ochraceus) preys on, albeit slowly, mussels and barnacles.

For the first time, researchers have mapped the worldwide distribution of a group of animals living at deep ocean sea floors. The location of the animals, known as brittle and basket stars, shows that food drives biodiversity in the deepest parts of the ocean. This runs counter to what happens on land and in shallower water, where sunlight is the primary driver, according to the authors of the study, which is published in the journal Nature. "On land and in the surface ocean, biodiversity typically peaks in or near the tropics and is lowest at the poles," co-author Derek Tittensor of the World Conservation Monitoring Center in the U.K. told Discovery News. He added, "Our analysis suggests that the deep sea may show a fundamentally different pattern, with biodiversity highest away from the equator and nearer high-latitude regions."

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The researchers decided to focus on brittle and basket stars because author Timothy O'Hara has been studying and collecting them for 15 years, lead author Skipton Woolley of the University of Melbourne told Discovery News. "Currently, no equivalent dataset exists for other taxa," Woolley said, indicating that the information on brittlestars and basketstars is unprecedented. He said that these photogenic animals "are ubiquitous in the deep-sea and are common in all deep-sea surveys." Tittensor added, "Other common deep-sea animals include various and often highly specialized fish species, nematodes (certain worms), crabs, crustaceans known as isopods, sponges, and many others." Basketstars are some of the most unusual looking animals on the planet. Encircled by a curly mass of tentacles is the creature's star-shaped mouth. They are a type of large brittlestar and can measure three feet across.

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Brittle and basket stars are close relatives of starfish, which exhibit an equally impressive array of sizes, colors and other features. Starfish, in turn, are not actually fish, but are instead creatures known as echinoderms. They are closely related to sand dollars and sea urchins. For the study, the researchers supplemented their data on brittle and basket stars with information on these animals found in scientific literature records as well as in museums around the world. The natural history collection in the Museum Victoria in Melbourne alone has over 16 million preserved specimens of these animals. Computer modeling was used to predict where the species occur. "From this, we could measure species diversity across the seafloor," O'Hara said.

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The researchers found that in the deepest parts of the world's oceans, at depths greater than 1.2 miles, biodiversity peaks at higher latitudes (temperate regions) than in the shelf and upper continental slope regions of oceans. The latter two areas are located at depths of about 65.5 feet to 6562 feet. The shelf and upper continental slope areas are in shallower water and therefore receive light and heat from the sun. The deep ocean seafloor has a completely different environment, though, which is unlike anything else on earth. O'Hara explained that the deep ocean seafloor is one of the earth's largest ecosystems. "It is cold, dark and subject to enormous pressure from the water above," he said, adding that "it receives oxygen from slow moving bottom currents, which take thousands of years to travel across the world's oceans." O'Hara continued, "The least explored of all Earth's ecosystems, it is very expensive to survey."

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Without sunlight to fuel photosynthesis, animals such as this banded brittlestar must rely upon nutrients originating from food that falls down from the shallower, sunlit parts of the ocean. Called "marine snow," the nutritious material consists of dead organisms, detritus, fecal matter and more. Brittle and basket stars directly eat such material as well as other deep-sea plankton and smaller creatures that have relied upon it. The ocean depths are also home to special communities of creatures that live around hydrothermal vents and cold seeps. Hydrothermal vents are openings in the seafloor out of which heated, mineral-rich water flows. Cold seeps are ocean floor areas where gases, such as hydrogen sulfide and methane, seep through into the seawater.

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Sometimes animals are spread out over vast distances in particular regions of the deep sea, and other times life is too close for comfort. In this case, a tropical brittlestar has wrapped itself around some coral. Thousands of tiny animals called polyps make up a branch or mound of coral. Woolley and his team found that patterns of biodiversity in the deep sea are so distinctive from terrestrial and shallower ocean ecosystems that they warrant their own unique realm or "third biome."

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The new study is likely the first of many that will map the distribution of particular groups of animals in the deep sea. Brittle and sea stars form just one unique group of many in this still-mysterious environment. As O'Hara asked, "How can we protect deep-sea animals and sustainably manage human activities, such as deep-sea fishing or mining, if we don't know where animals live?"

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