How will the rest fare as seawater chemistry changes?
An array of marine organisms, including urchins, crabs, and mussels, build up their hard shells and skeletons with the mineral calcium carbonate. These marine calcifiers often inhabit waters full of dissolved carbon dioxide, which turns the oceans acidic, and can theoretically eat away their calcium-rich structures.
But in practice, nearly a quarter of marine calcifiers worldwide already living in highly acidic seawater have strong shells, according to a new study published in Global Biogeochemical Cycles.
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"The result surprised us a lot,” said study lead author Mario Lebrato, from the Institute of Geosciences at Kiel University, in a press release. “For us, it is a sign that many marine organisms actually can live and maintain their calcareous shells under chemically unfavorable conditions which may reflect their physiological and evolutionary history."
Many of the studied species frequently incorporate magnesium into their shells, which makes them even more vulnerable to acid. The researchers investigated the degree to which the seawater in which a given species lives is saturated with minerals needed to build their hard parts, and then compared it to the species’ susceptibility to deterioration.
Their results “reveal a surprisingly high proportion of benthic marine calcifiers exposed to seawater that is undersaturated with respect to their skeletal mineralogy,” the researchers write, noting that ongoing ocean acidification over the next hundreds and thousands of years will expose an estimated 57 percent of marine calcifiers to seawater deficient in the minerals they require.
Although it is impressive that so many species maintain their shells and skeletons under harsh conditions, their overall health was not examined in this study. And of course, 24 percent of species are able to withstand a mineral-poor, acidic environment, but it is something the other 76 percent have not experienced — how those species will cope with future ocean acidification remains to be seen.
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