Marine Life & Conservation
Researchers Claim Dissolving Snail Shells Are An Effect of Ocean Acidification
An increasingly acidified Pacific Ocean is dissolving the shells of tiny marine snails that live along North America’s western coast. The broad finding, which has surprised some researchers, suggests that sea life is already being affected by changes in the ocean’s chemistry caused by rising carbon dioxide levels in the atmosphere.
“It really changes the game by demonstrating that acidification is having a noticeable impact,” says biological oceanographer Jan Newton, co-director of the Washington Ocean Acidification Center at the University of Washington, Seattle. Newton was not involved in the study.
The researchers studied one kind of pteropod, common planktonic snails known as sea butterflies for the winglike body parts that help them glide through the water. Like other shellfish, pteropods use dissolved carbonate in seawater to build their shells. But laboratory studies have shown that the process can be disrupted, and shells can dissolve as seawater becomes more acidic, or lower in pH (temperature has an impact, too). As its concentration rises in the atmosphere, carbon enters the ocean through chemical reactions, causing its pH at the surface to drop by 0.1 units since the pre-industrial era. That’s raised fears that marine ecosystems could be affected.
Outside the laboratory, however, just a handful of studies have linked falling pH levels to damaged shells. In 2012, researchers documented damage to oysters in hatchery tanks in Oregon fed with seawater that had become more acidic as a result of offshore upwelling patterns. The same year, researchers reported that pteropods collected at one site in the Southern Ocean around Antarctica showed signs of shell damage.
To gauge how acidification might be affecting the Pacific, biological oceanographer Nina Bednaršek of the National Oceanic and Atmospheric Administration (NOAA) in Seattle and colleagues collected pteropods at 13 sites during a 2011 research cruise between Washington and southern California. Back at the lab, they used a scanning electron microscope to examine the fragile shells, which are 1 cm in size or smaller. Normally, healthy pteropods have smooth shells. But more than one-half of these shells showed signs of dissolution, they report in the Proceedings of the Royal Society B. The pitted textures made them look like “cauliflower” or “sandpaper,” Bednaršek says.
“I was surprised by the sheer spacial extent of the dissolution,” she says. “This is something we have not predicted before – the extent of the population that’s already affected.”
What’s not clear from this study is how such damage might be affecting pteropod populations or the broader ecosystem. Previous work has suggested that shell damage can make it harder for the invertebrates to fight infection, maintain metabolic chemistry, defend themselves against predators, and control buoyancy. And while the snails are one of the most abundant organisms on Earth, “their role in ecosystems is generally not all that well known,” writes biological oceanographer Gareth Lawson of the Woods Hole Oceanographic Institution in Massachusetts in an e-mail. But “they can be important prey items at some times and places” for fish and other creatures. For example, the pteropod examined in this study, Limacina helicina, is a key food for fish eaten by pink salmon, an important North Pacific fishery.
“If the pteropod shells are dissolving as fast as the authors claim, the effects on individual physiology, behavior, and fitness, and hence on populations and food webs, are not easy to predict,” Lawson says. “But they could be profound.”
The waters probed during this study, known as the California Current, are a hot spot of ocean acidification because of coastal upwelling, which brings naturally acidic waters to the surface, where they are made even more acidic by greenhouse gas pollution. But Richard Feely of NOAA, a co-author on the study, says that the site serves as a “harbinger” for what global seas will be experiencing decades hence.
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Marine Conservation Society’s wildlife sightings project asks beachgoers to share their discoveries and contribute to research
The Marine Conservation Society’s long-running wildlife sightings project focuses on two key species which arrive on UK shores: jellyfish and, as a result, turtles. Both species are vital in supporting ocean biodiversity and are indicators of climate change while being at risk from its impacts.
The charity is asking beach and seagoers to share when they spot either of these marine animals to support ongoing research.
During spring and summer, jellyfish arrive in the UK’s warming waters to feed on plankton blooms or, in fact, anything small enough to get caught. To that extent, jellyfish feed not only on plankton, but also the array of eggs and larvae of fish, crustaceans, starfish and molluscs which rely on plankton as a stage of reproduction.
With healthy fish stocks and rich biodiversity, jellyfish quickly become part of an effective food chain. Everything from tuna to turtles will feed on jellyfish of various sizes, so the population is well controlled. Supported by a rich and diverse ocean ecosystem, jellyfish link the microscopic world of plankton to larger marine animals and the ocean around them.
Jellyfish are especially appealing for marine turtles. Six of the world’s seven marine turtle species have been spotted in UK seas as a result of jellyfish blooms in spring and summer.
The largest sea turtle, and the most common in UK seas, is the leatherback which has a ‘vulnerable’ conservation status. Reporting sightings of these incredible creatures will support the Marine Conservation Society and others in understanding their movements, potential threats and how to better protect them.
Amy Pilsbury, Citizen Science Project Lead at the Marine Conservation Society, said:“For more than 17 years, beachgoers across the UK have been contributing to scientific research by sharing their wildlife sightings with us. It’s a key part of our work and plays a vital role in better understanding and protecting our ocean.”
In 2014, with partners from the University of Exeter, the Marine Conservation Society published the first paper from the survey data, confirming key information about UK jellyfish and including the first distribution maps of the surveyed species.
Since the 2014 paper, the wildlife sightings project has recorded notable events such as massive and extensive annual blooms of barrel jellyfish and several summers of Portuguese Man o’ War mass strandings.
The charity continues to run its wildlife sightings project to see what happens to the distribution and frequency of mass jellyfish blooms over time. The data will help to explore any links jellyfish blooms have with big-picture factors such as climate change.
Jellyfish can be spotted year-round in UK seas, but larger blooms are more likely to appear in spring, lasting through until autumn. Jellyfish sighting records from 2021 suggest that compass jellyfish are the most common around UK shores, making up 36% of reported sightings.
| Jellyfish species | Percentage of sightings reported |
| Compass jellyfish | 36% |
| Moon jellyfish | 17% |
| Lion’s mane jellyfish | 15% |
| Barrel jellyfish | 14% |
| Blue jellyfish | 9% |
| Portuguese Man o’ War | 6% |
| Mauve stinger | 2% |
| By the wind sailor | 1% |
For more information on how to identify jellyfish and turtles, and to report a sighting, please visit the Marine Conservation Society’s website.
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