The Case of the Disappearing Oyster

As we enter into the heart of the summer and our plates abound with fresh seafood, you may be hearing that our oceans’ pH is dropping to make the waters more acidic. This phenomenon, more commonly known as ocean acidification (or OA for short), can make life pretty tough for all those shellfish you love to eat like oysters, mussels, and blue crabs. In this post, we’ll take a closer look at exactly what ocean acidicification is and offer a glimmer of hope that those oysters you love to eat may be able to cope with OA better than we previously though.

So what does the term ‘ocean acidification’ really mean? If you think it sounds like a bunch of science jargon, you wouldn’t be far off. Without giving you an entire chemistry lesson, I’ll boil it down to the high points.

where_does_carbon_go
Where do our carbon emissions actually end up? Source: SUNY Suffolk

The first thing we should start with is an understanding of where all the CO2 (carbon dioxide) from burning fossil fuels actually goes when it’s released. Our oceans actually have a very large capacity to absorb CO2 out of the atmosphere. In fact, since the Industrial Revolution, the oceans have absorbed about half of the carbon emission from humans! And, on a daily basis, the oceans absorb a quarter to  a third of CO2 released.

Once absorbed into the ocean, CO2 can go to one of three places:

  1. The shallow ocean water where it stays for a matter of minutes to years
  2. Deep ocean waters where it stays for hundreds to thousands of years
  3. Ocean floor/sediment where it stays for millions of years

And in more temperate and polar waters, this issue is even more pronounced – in these colder waters, CO2 is absorbed in much greater concentrations!

So, why do we really care how much CO2 gets absorbed into the oceans?

Increased levels of CO2 can have profound impacts on a number of species, namely shell-forming animals like oysters and mussels and our beloved blue crabs and lobsters.

Now that we know where our carbon emissions actually end up, let’s review a little chemistry…I promise it won’t be too painful. We need to cover two basic points and then I’ll get back to the good stuff.

When COmolecules are absorbed into the ocean, the molecules react with water to form an acid called carbonic acid, or H2CO3. Now, think back to your early chemistry days…can you remember conducting an eggshell-acid experiment like this one?

You can see that when an acid (the vinegar) and a base (the eggshell) react, the acid eats away at the base. This disintegration of the eggshell is what is happening to the shells of shellfish as the ocean becomes more acidic.

Enter the oyster.

The impacts of ocean acidification have already been severe in the Pacific Northwest. In fact, nearly 10 years ago, production at Washington oyster hatcheries began drastically declining and oyster shells seemed to be dissolving before our very eyes. Because colder waters absorb CO2 and acidify more quickly, this region is considered ground zero for ocean acidification. Unfortunately, the New England region is not far behind.

There has been a lot of doom and gloom news about ocean acidification and its impacts on many commercially and ecologically important species like summer flounder, oysters, and sharks.

But wait…there is hope!

There are some organisms that are actually doing alright in the face of ocean acidification. And scientists recently found another one.

Researchers discovered that native Olympia oysters, which were once abundant along the Pacific Northwest until over-harvesting and habitat loss all but wiped them out, actually have a built-in resistance to ocean acidification!

olympia oysters
Olympia oysters growing in Yaquina Bay, Oregon. (Source: Oregon State University)

Their ability to withstand acidifying waters lies in the fact that they don’t start building their shells until they are 2-3 days old. Compare this with commercially raised Pacific oysters, which start building their shells at just 6 hours old. This means that when these oysters are the most vulnerable, they’re able to invest more in other bodily processes than in building a shell – effectively increasing their chances of survival.

So what gives?

Maybe you noticed that there is a tradeoff here. But it may not be what you think…

Mama Olympia oysters actually produce larger, but fewer, eggs. Mama Pacific oysters, on the other hand, produce tens of millions of much smaller eggs. Because of the initial devotion of mother Olympia oysters – she’s spending her energy to produce bigger eggs – baby Olympia oysters are able to spend less of their own energy on immediate growth and shell-building and focus on coping with acidic waters. In contrast, baby Pacific oysters, because they are smaller, must begin spending their energy on growing their shell almost immediately, so they are left with little energy to deal with acidic waters. In fact, scientists at Oregon State University found that relative energy stores of young Pacific oysters declined by 38.6 percent an hour, and only 0.9 percent in Olympia oysters.

So what does this mean for your love of oysters?

Well, don’t panic just yet. This research highlights the robust response to ocean acidification that might be inherent in even more organisms. Researchers are working hard to better understand organisms’ response to ocean acidification and as this research continues, fingers crossed that we will find more organisms that have built-in mechanisms designed to help them withstand acidifying waters…especially delicacies like oysters!

Additionally, this research has big implications for the future of the commercial oyster industry. Because many of the problems for oysters resulting from ocean acidification seem to originate at very early developmental stages, understanding how Olympia oysters overcome these problems could prove beneficial for oyster hatcheries. Cultivating native oysters could help safeguard Washington oyster farms against losses due to ocean acidification. It may also be possible to instill some of the Olympia’s oysters beneficial traits into Pacific oysters through selective breeding programs.

 

 


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