Oyster Osteoporosis

Ocean Acidification ProcessImage: NOAA Pacific Marine Environmental Laboratory

Ocean Acidification Process
Image: NOAA Pacific Marine Environmental Laboratory

Another day, another coal mine canary.
The Pacific Northwest is well-known for its oyster farms. I have friends who have been oyster farmers for years. I always think of oysters as being rough, thick-shelled, resistant creatures. Which they are, once they are mature. The ocean acidification process that has affected other calcifying species elsewhere in the world isn’t yet particularly dangerous for mature oysters.

What it affects in a dramatic manner are the oyster larvae. The rate at which their newly forming shells can take up enough calcium to protect them into maturity is outpaced by the rate at which the shells are dissolved by the amount of CO2 in the acidified seawater. Up to 80% of the oyster stocks have been lost over the past few years in some areas.

There are undoubtedly a number of different reasons for this kind of annual die-off. One stated cause is the geographic location of the Pacific Northwest, where long-term oceanic currents pull up water from deep sea depths, and corrosive waters that absorbed the massive carbon dioxide industrial emissions of the mid-twentieth century are spewed right into some of the world’s richest fisheries. Other possible causes – bacterial infections, pollution due to agricultural run-off, lack of sufficient amounts of phytoplankton, normal fluctuations in seawater quality, etc. – could likely also play a role.

The comment sections for the many articles on this topic are spiked with a large number of what look like well-informed contributions that dispute ocean acidification as the ‘real’ reason for this particular dramatic species decline, with arguments ranging from standard-issue climate change denial to frontal attacks on the researchers and journalists for not giving enough weight to whatever pet cause the commenter favors, be it pollution or bacteria or the sheer unknowability of specific life cycles in all their complexity.

Lively conversation and discussion are all fine and well, but – leaving aside the obvious cranks who just want the conversation to stop altogether – it is frustrating to see disputes that can be implemented and leveraged by those with an economic interest in fighting any changes that need to be made. It is frustrating to see these kind of arguments serve to confuse (or worse, bore) observers who are only marginally inclined to engage in the discussion in the first place, much less take action. It’s this kind of counter-productive discourse that leads to reactive rather than proactive policy-making.

Keeping in mind that if the acidified waters now upwelling in the Puget Sound and elsewhere along the coast are fifty years old, the next fifty years of industrially-impacted seawater is still yet to come. And the United States government states it is actually pleased with new signs that it will soon be the world’s leading oil supplier, not a promising course of development if what we need to do is reduce carbon emissions in the very country that is among the leaders in the reliance on carbon-based fuel.

Is this the only reason? Undoubtedly not. So what harm could it do to work on expanding phytoplankton populations, curbing agricultural run-off, and so on? As always, whatever the economic cost of immediate change might be, it won’t be any less if we wait.

Meanwhile, oyster farmers are doing what they can to save their $270 million/year industry. Reactive policy-making in some places means simply dumping large amounts of pH-balancing sodium bicarbonate into oyster beds in the hope that the oyster larvae will make it past the earliest phases and into adulthood.


Trouble in the Water: Acidifying Oceans Hinder Health of Northewest Shellfish

Yale Environment 360

National Oceanic and Atmosphere Program

Thank you, flying shell creatures

Limacina helicina Photo: Alexander Semenov

The pteropod Limacina helicina, a tiny sea animal that is usually under 1 cm in length, swims through the open ocean. They are a food source for birds, whales, fish, and other sea animals only slightly larger than themselves. They feed on plankton and float in large colonies, flapping their wing-like lobes. They have fragile, almost transparent shells that are present during the entire life cycle of many sea butterfly species. It is these shells which are the object of interest today.

Clione limacina: Sea butterflies are the primary food source for the sea angel (Gymnosomata), a shell-less sea slug.

According to the British Antarctic Survey (BAS), while carrying out research in the Southern Ocean together with other institutions, discovered severe dissolution of the shells of living sea butterflies, i.e. the shells are being dissolved by the raised acidity of oceans due to increased levels of atmospheric CO2 being absorbed by oceanic systems . Why is this important?

On one level, it’s bad for the sea butterflies themselves, even if they don’t die from their shells being dissolved. They are more vulnerable to disease and predators. According to Dr. Geraint Tarling, co-author of the study, “As one of only a few oceanic creatures that build their shells out of aragonite in the polar regions, pteropods are an important food source for fish and birds as well as a good indicator of ecosystem health.”

But there are enough indifferent climate observers who aren’t really interested enough in a specific ecosystem, even if it might impact the amount of fresh seafood on the dinner plate, to make the sea butterfly’s plight a point of concern, much less action.

So, aside from the biological relevance of the sea butterfly, their shells form an important component in the global carbonate cycle, part of which is the deep-sea calcium carbonate sediment formed by the remains of creatures like the sea butterfly. This sedimentary sink of CaCO3, which gathers like deep-sea snow in the form of discarded shells from the sea butterfly and many other animals, forms a buffering process between ocean chemistry and atmospheric CO2 by neutralizing the acidic influence of the carbon dioxide.

Prior to the evolution of creatures with calcium carbonate shells in the ocean, the global atmosphere is thought to have been far more volatile – these shells helped mitigate the carbon cycle at shallower ocean levels and lead to an extended period of the more stable atmosphere which we humans need to thrive.

The tiny sea butterfly is thought to comprise up to 12% of the global ‘carbonate flux’. For their miniscule size, they are heavy hitters in the atmospheric game. Their shells are the thinnest and most fragile. They are, not to belabor an overused metaphor, the little canaries in our atmospheric coal mine.

So, the next time we read about the relief felt over the discovery of a new fossil fuel source or promising new extraction technology, spare a thought for the sea butterfly, and keep your fingers crossed that our skin is thicker than their shells.


* Press release: First evidence of ocean acidification affecting live marine creatures in the Southern Ocean (BAS)

* Paper: The role of the global carbonate cycle in the regulation and evolution of the Earth sytem, Ridgewell/Zeebe