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.
Stranded dolphin rescued from muddy inlet
At around 11:40 on Friday 16 February, a lone common dolphin was reported to British Divers Marine Life Rescue circling in the shallows in an inlet at Place, near Portscatho, in Cornwall. A couple of volunteer Marine Mammal Medics were sent down initially to monitor the animal in hope it would be able to get away by itself, and further assess the situation.
After an hour and a half or so of observation, the risk of stranding increased significantly as the tide went out as the inlet is very shallow, muddy and almost completely dries out over low tide. Therefore, a larger response team was dispatched with more equipment in preparation for a stranding. Indeed, the animal did soon strand in the mud and fell onto its side, submerging the blowhole. Luckily the team were on hand to help get it upright again quickly, then bring it ashore for a health assessment and to begin providing first aid. No obvious injuries could be found and it measured 2.03m, later confirmed as female.
The team were soon joined by two vets, who were able to confirm the animal to be in moderate nutritional condition and appeared otherwise okay following a more detailed health check, and so was suitable for the team to attempt to refloat. However, it was not possible to refloat it safely in the inlet due to the nature of the geography, substrate and tide there it seemed the most likely reason this dolphin had stranded was due to getting disoriented in this location, and would struggle to get out again. Luckily a local resident had his boat tender moored nearby and was happy to use it a transport craft to take the dolphin out to deeper water.
With help, the boat was slid across the mud and launched near the mouth of the inlet. A surfboard was placed on one side with a soft mat on top for the dolphin to lie comfortably on during the journey. When ready, the dolphin was carried across in a tarpaulin, transferred to a mesh stretcher and loaded on board with a team of four Medics including a vet.
The boat then carefully made its way out to the mouth of the Percuil River, facing into Carrick Roads and close to open sea, which was the most ideal site for release where the chance of returning and re-stranding was lower. The dolphin was carefully hauled overboard in the stretcher and held alongside briefly, though as she started kicking strongly almost straight away it was hard to keep hold and so she was released quickly. The boat retreated and the team observed her circling in the middle of the channel until she was lost from sight. The team returned to the inlet before darkness fell.
The area will be monitored over the weekend for re-sightings or re-strandings, but it is hoped that she will recover successfully and continue back out to sea. In the meantime BDMLR would like to thank the volunteer team, local residents and members of the public for all their efforts and support throughout this incident.
British Divers Marine Life Rescue is an international marine animal rescue organisation based in the UK and is a registered charity. The aims of the organisation are to provide a rescue service for marine wildlife, to support existing rehabilitation centres and to develop new methods of rescue, treatment, transport and care. Website www.bdmlr.org.uk.
Photos: Dan Jarvis
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