Cold-water species hit hardest by increased levels of carbon dioxide
By Summit Voice
SUMMIT COUNTY — The effects of ocean acidification on shellfish are widespread around the globe and may be the most pronounced at high latitudes with low water temperatures, according to new research that examined a wide range of species from the tropics to the Arctic.
But there is some evidence that, with enough time, shellfish and other marine organisms may be able to adapt to the changes caused by global warming, according to the study published this week in the journal Global Change Biology.
“In areas of the world’s oceans where it is hardest for marine creatures to make their limestone shell or skeleton, shellfish and other animals have adapted to natural environments where seawater chemistry makes shell-building materials difficult to obtain,” said Dr .Sue-Ann Watson, formerly of the University of Southampton and British Antarctic Survey (now at James Cook University) said. “Evolution has allowed shellfish to exist in these areas and, given enough time and a slow enough rate of change, evolution may again help these animals survive in our acidifying oceans.”
Oceans are becoming more acidic because some of the increased carbon dioxide humans are adding to the atmosphere dissolves in the ocean and reacts with water to produce an acid. That makes it more difficult for clams, sea snails and other species to extract calcium carbonate from seawater to build their shells and skeletons.
The study was conducted by scientists with the British Antarctic Survey and the National Oceanography Centre, together with colleagues from Australia’s James Cook and Melbourne Universities and the National University of Singapore.
The researchers looked at natural variation in shell thickness and skeletal size in four types of marine creatures living in 12 different environments from the tropics to the Polar Regions. Their aim was to get a clearer understanding of similarities and differences between species, and to make better predictions of how these animals might respond to increasing acidity in the oceans.
The four different types of marine animals examined were clams, sea snails, lampshells and sea urchins. Scientists found that as the availability of calcium carbonate decreases skeletons get lighter and account for a smaller part of the animal’s weight. The fact that same effect occurs consistently in all four types suggests the effect is widespread across marine species, and that increasing ocean acidification will progressively reduce the availability of calcium carbonate.
The results show that, over evolutionary time, animals have adapted to living in environments where calcium carbonate is relatively difficult to obtain by forming lighter skeletons.
Shellfish are an important food source for marine predators such as tropical seabirds and seals, as well as being a valuable ingredient in human food production. Consequently, these changes are likely to affect humans and the ocean’s large animals.
The amount of effort required for shell-building varies from place to place in the world’s oceans, based on other factors, including temperature and pressure. There is already evidence that ocean acidification is affecting the ability of some marine species to grow, especially during their early life stages, and there is mounting concern about whether or not these species can evolve or adapt to cope with increases in acidity in the coming decades.
“This effect is strongest at low temperatures and the results showed polar species to have the smallest and lightest skeleton, suggesting that they may be more at risk in the coming decades as the oceans change,” said Professor Lloyd Peck, of the British Antarctic Survey.
“Interestingly, where ecology requires animals to have strong skeletons — for instance to protect them from impacts from floating ice in Antarctica -—skeletons are made thicker and stronger. However, they still form a smaller part of the animal’s body mass, because the shape of the species changes to enclose much more body for a given amount of skeleton,” Peck said. “Thus life finds a way, but still follows the overall trends of decreasing skeleton size in areas where the ocean chemistry makes it more difficult to obtain the necessary building blocks. If there is time for species to evolve in temperate and tropical regions it is one way they may be able to overcome some of the future effects of ocean acidification.”
“In areas of the world’s oceans where it is hardest for marine creatures to make their limestone shell or skeleton, shellfish and other animals have adapted to natural environments where seawater chemistry makes shell-building materials difficult to obtain. Evolution has allowed shellfish to exist in these areas and, given enough time and a slow enough rate of change, evolution may again help these animals survive in our acidifying oceans.”