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Saving Coral Reefs — With Sex

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Saving Coral Reefs — With Sex
Rebecca Albright in the California Academy of Science's darkroom where they are working on coral spawning and restoration efforts. Tara Lohan

By Tara Lohan

Visitors walk slowly through a room of dimmed lights and glowing tanks that bring the mysteries of the sea into plain view. The Steinhart Aquarium at the California Academy of Sciences in San Francisco is home to 900 different species — everything from brightly colored reef fish to prickly sea urchins, even an albino alligator named Claude.


But some of the most exciting things to see are out of the public's view.

In a specially constructed darkroom in one of the labs, scientists are coaxing corals to spawn and studying how to increase the chances of survivorship for baby corals. It's all part of a larger effort to give threatened reefs — and all the species that depend on them — a fighting chance.

Reefs at Risk

Shallow tropical reefs face a long list of threats including overfishing, disease and pollution, but one of the biggest dangers is climate change, which is contributing to rising sea surface temperatures and increasing ocean acidification. It's estimated that in the past 30 years half the world's coral reefs have died and by the end of the century we could lose 90 percent.

That's bad news for millions of people and marine life.

Coral reefs have important biodiversity and economic values. Reefs are like rainforests, providing food and shelter to thousands of other species. Coral reefs cover just 0.1 percent of the ocean floor, but they host more than 25 percent of the ocean's biodiversity. "So if we lose them, then we lose a disproportionate amount of biodiversity," said Rebecca Albright, a coral reef biologist who co-leads the California Academy of Science's Hope for Reefs initiative that works on researching and restoring coral reefs.

Reefs also provide key ecosystem services, valued at an estimated at $375 billion a year. Coastal communities rely on subsistence and commercial fishing supported by reefs, and their beauty and biodiversity bring in big tourism dollars. Reefs also provide a buffer for shorelines, helping to protect against storms and erosion — increasingly expensive threats with climate change.

Albright spent years studying what was going wrong with reefs. "I've done a lot of work looking at impacts of ocean acidification on reproduction and coral settlement and there's not a lot of good news there," she said.

So she shifted her focus.

"If we're losing corals at an unprecedented rate, then the only way we're going to get them back is if they can reproduce or grow more quickly."

Coral Reproduction

Corals and algae grow in a lab at the California Academy of Sciences.

Tara Lohan

To understand how scientists are hoping to help save corals, you need a quick primer in coral reproduction.

Most corals can reproduce in two ways. There's asexual reproduction — like a starfish, you can break off a piece of coral and the fragment will regenerate. Many conservation efforts have (and continue to) focus on fragmenting corals and then planting them back out onto reefs. These kinds of efforts work well at the hectare scale, said Albright, but they're not effective for ecosystem-wide restoration. At this rate we're a long way from being able to keep pace with the rate of environmental loss.

"You can imagine it's very laborious and time consuming," she said. "And when you look at the fact that we've lost 50 percent of the Great Barrier Reef, which is 2,300 kilometers long, individual divers going out and physically planting onto the reef is just not scalable."

Corals, however, can also reproduce sexually. Synchronized reproductive events happen in a rather dramatic fashion — usually just once a year for most corals, and for many it's at the end of the summer, after sunset and following a full moon, said Albright. Eggs and sperm are "broadcast" into the water column, where they combine and fertilize to produce larvae that eventually fix themselves to the ocean floor or other hard surfaces where they begin to grow from individual polyps into a colony. It will be a few months before the growing coral is even visible to the naked eye.

Understanding these reproductive processes could help solve another natural problem: Some reefs are currently dominated by a single clone and that low genetic variation can lead to disaster in times of environmental change. It's of special concern now as corals try to adapt to warming waters.

Sexual reproduction is "the only avenue for genetic diversity and so that's the one that we're focused on right now," said Albright.

"So what we're trying to do is just focus on helping corals sexually reproduce, get as much genetic diversity out there as possible and then let nature pick which ones win and which ones lose, because that's how it's supposed to happen," she said.

Spawning in Captivity

At the California Academy of Sciences darkroom, Albright and her team have built a special environment filled with tanks programmed to simulate the seasonal temperature and light changes of the Palau archipelago, home to the staghorn corals (Acropora cervicornis) they're growing.

This complex process, which took a year and a half to develop, provides a unique opportunity to observe not just the reproduction but what happens to the resulting larvae, helping the researchers to better understand what may help more larvae make it to maturity out on the reef.

In nature, that's not an easy task. Life is tough for a microscopic coral on the ocean floor — there are endless things that could eat or outcompete it. Only about one in a million survive.

"The goal here is just to figure out how to get these corals to produce more offspring that are more viable and then use that knowledge to help field efforts," said Albright. "If we can increase survivorship by 10- or 100-fold, then that would be hugely helpful." This is especially true for reefs that are already depleted.

Rebecca Albright examines baby corals spawned in the lab under a microscope.

Tara Lohan

One of the things her lab will study over the next several years is whether energetic enhancements, like better nutrition, can help corals like they do in early life stage for humans.

"If you could add things that would make the larvae more energetically replete, would that translate into better post-settlement survivorship?" she asks. "We'll be looking at that, along with how different [water] flows may make them grow faster and other ways to enhance their survivorship."

Hope for Corals isn't the only project out there trying to save corals. Other scientific efforts are studying how to get corals to be more robust against stress or to selectively breed "super corals" that are more resistant to heat or other pressures. Albright said she's heartened by this broad array of scientific efforts. "I think the solutions that are being explored by working at the intersection of disciplines like biology, engineering and technology are the most exciting as they have high capacity to help us scale results to meaningful levels," she said. "Most of that work is in early days but is exciting in terms of potential."

But she admits, there's still a long way to go, much to learn and no magic bullet for reefs.

Also, the clock is ticking.

"We're losing things so quickly right now, most conversations are switching towards talking about saving certain things and where we focus our efforts — because we can't save everything," she said.

Reposted with permission from our media associate The Revelator.

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Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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