The greatest threat facing the ocean, namely rising levels of carbon dioxide in the atmosphere, actually poses two distinct threats – warming and acidification. Each will get its day in the “Discovery of the Year” spotlight. Today, it’s ocean acidification’s turn.
As you may recall, ocean acidification is the phenomenon in which carbon dioxide from the atmosphere dissolves in the surface waters of the ocean, producing carbonic acid that (in sufficient quantities) shifts the pH balance of the ocean toward acidity and impairs the ability of animals like oysters and corals to extract the calcium carbonate they need to build their skeletons or shells. In the past 200 years, the ocean has absorbed nearly a third of carbon dioxide emissions, resulting in a 30% increase in ocean acidity.
Scientists have generally considered the impacts of ocean acidification to be a problem of the (near) future. But in September 2010, two marine scientists from Stony Brook University – Stephanie Talmage and Christopher Gobler – published a paper in the Proceedings of the National Academy of Sciences that forced a revision of that thinking, suggesting that ocean acidification may already be (and have been for some time) taking a toll on shellfish.
WHAT WE KNOW (and HOW WE KNOW IT)
Talmage and Gobler reared quahogs (Mercenaria mercenaria) and bay scallops (Argopecten irradia) under conditions simulating past, present, and likely future carbon dioxide levels. Not surprisingly (because numerous previous studies have documented similar findings), the shellfish of the future had severe shell defects, higher death rates, and slower growth than their modern-CO2 counterparts. What was less expected was the observation that modern conditions produced shellfish with thinner shells, slower growth, and death rates almost double those of shellfish grown in pre-industrial water conditions.
WHAT IT MEANS
Talmage and Gobler conclude that ocean acidification “may [already] be inhibiting the development and survival of larval shellfish and contributing to global declines of some bivalve populations.” In fact, since shellfish grown in the laboratory are granted a relatively luxurious life with abundant food and no predators or competitors, the authors say their data represent conservative estimates of the impacts of acidification. In the wild, slow-growing, thin-shelled animals would likely be vulnerable to any number of untimely ends – predation, over-crowding, incidental crushing. Stressed animals may also be more susceptible to diseases, like those that have ravaged east coast oyster populations in recent decades.
WHAT WE DON’T KNOW
With ocean acidity reaching levels not seen in over twenty million years, perhaps the biggest question on many scientists’ minds is whether evolutionary adaptation will be able to keep pace with rising acidity.
Heather Goldstone, CLIMATIDE, 5 January 2011. Article.
