Researchers see ‘future of an entire species’ in ultrasound technique, Science News

Kristin Aquilino, a scientist at the University of California, Davis, knows that expectations are disappointments in disguise. For the past decade, she has led the school’s white abalone captive breeding program, which aims to bring the marine mollusk back from the brink of extinction.

In June, she and her colleagues drove snails held in Davis’s captivity along the California coast to the Cabrillo Marine Aquarium in Los Angeles. Others have been deposited in laboratories and aquariums in Southern California; Altogether, this was the largest white abalone spawning attempt to date. But when she tried to get them in the mood with what she calls a love potion – a mixture of seawater and hydrogen peroxide – the snails languished in their tanks sometimes emitting bubbles, but no eggs or sperm. After four hours, Aquilino called it off. (Concurrent attempts on the other sites also failed.)

“It sucks,” she said. “There’s a lot of human effort involved, but there’s no way they’re happening today.”

After fishermen depleted 99% of white abalone in the wild in the 1970s, sea snails are hanging by a slimy thread. Despite the urgency to breed these and other endangered aquatic snails to reintroduce them into the wild, propagating more of them in a lab remains a guessing game, says Aquilino.

Now, a study published Thursday in the journal Frontiers in Marine Science offers an improved tool for determining which abalone will breed. The technique – using non-invasive ultrasound, a decades-old medical technology – could increase the chances of successful captive breeding efforts and ultimately help restore the endangered abalone to the wild. .

“If we can use this method, it could make a very big difference and we could strategically target animals to induce them to spawn,” said David Witting, a fisheries biologist with the National Oceanic Atmospheric Administration who specializes in abalone recovery. . not involved in the study. “We will take any additional advantage we can get. Getting the animals to spawn is really the critical point of the whole recovery process. »

For Aquilino, the method offers a glimmer of hope.

“When I first saw the ultrasound images of my children, I saw the future of my family,” she said. “When I see the ultrasound images of these abalones, I see the future of an entire species.”

Seven species of abalone – sea snails with colorful domed shells – have historically made their home on the west coast of North America. Animals help the ecosystems they live in by tending kelp forests, feeding marine mammals and improving reef health.

But for much of the 20th century, divers and fishermen depleted several species of abalone. Along with the white abalone, the black abalone has succumbed to a disease called wilt syndrome, and the pinto abalone in the North Pacific has suffered from overexploitation and habitat degradation. In the wild, abalones are terrible at long-distance relationships: to reproduce, they must be close to each other because snails send their gametes into the water column to fertilize each other. In the 1990s, there were so few endangered species that scientists realized they had to intervene.

However, breeding them in captivity is a tall order. There are no clear clues as to when they are ready to breed. Researchers have traditionally visually inspected snails by removing them from the surface they’re being sucked onto, then searching the crevice between their sticky feet and shell for a bulge, where the animal’s gonad sits under the milky skin. . Depending on the size of the gonad, scientists assign a score to the animal: plump protrusions outweigh smaller ones.

“This type of gives you an idea of ​​whether the animal can spawn or not,” said Josh Bouma, abalone program manager for the Restoration Fund in Washington state, which runs the pinto abalone captive breeding program. endangered.

But visual examinations can be very inaccurate. The gonad surrounds their stomach, so if the snail has just had a huge meal, the score can be misleading. The researchers could also take a more precise tissue sample, but that would kill the snail. And handling abalones in any way — including pulling them out of their aquarium tanks — is enough to stress them out and can kill their mood.

Ultrasound, on the other hand, is non-invasive.

The idea of ​​using ultrasound on these snails originated in 2019. Jackson Gross, an aquaculture specialist at the University of California, Davis, had used ultrasound on finfish, such as sturgeons, to study their breeding habits. He came across a YouTube video of a vet slipping an ultrasound probe deep inside a land snail. If it worked for land snails, wouldn’t it also work for sea snails like abalone?

Sara Boles, a postdoctoral researcher working with Gross, discovered a way to perform ultrasound on abalones without taking them out of their tanks by holding the device up to their sticky feet. This quickly produced clear images of their swollen or flaccid gonads on a laptop attached to the ultrasound probe.

In the new study, Boles and his colleagues examined more than 200 abalones and scored their gonad thickness on a scale of 1 to 5 to determine which ones are likely to spawn. With ultrasound images, the gonad is in focus: the stomach appears as a dark cone-shaped feature, and the slightly lighter gonad surrounds it.

For now, these images may provide an easy way to score animals, but Gross and his colleagues want to test whether gonad thickness also correlates with reproductive success.

Already, Boles has used ultrasound to help Aquilino in his efforts to raise white abalones. Last spring, after Aquilino had already visually marked the animals, Boles brought the ultrasound to his lab.

Of the eight white abalone Boles ranked highest after ultrasound examination, five sired; some snails with slightly lower ratings also did. The method is already helping researchers revise their methods for assessing which abalones are most ready to reproduce.

“It’s another way of making sure we have the best of the best,” Boles said.

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