Ocean Acidification Is the Evil Sidekick Nobody Asked For

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school of fusilier fish
The more acidic things get, the less happy these guys will be. Photo by Nhobgood, CC BY-SA 3.0, via Wikimedia Commons

Climate change is the ultimate supervillain. The existential crisis of our time. It’s too late to stop it now. It will harm us, our societies, our biosphere and ecosystems, our food supply. That’s the best case scenario, significant but manageable harm. Our struggle now is to keep it from altering the planet in ways we cannot adapt to or recover from. As evil supervillains go, climate change is the sort that makes the other supervillains team up with the good guys, because even they’re afraid of it. You knew all that already. But, did you know that climate change has an evil sidekick? Ocean acidification goes hand in hand with climate change, tagging along while working on its own devious scheme. And the general public almost never hears about it.

You probably already know that carbon dioxide emissions are the main force driving the climate crisis. While CO2 isn’t the only greenhouse gas that human activity produces, or even the worst one, it’s released in such huge quantities that it easily overshadows more dangerous but less common gases like methane or nitrous oxide. What you may not have known, however, is that there’s a natural process that simultaneously removes CO2 from the atmosphere while creating a whole new problem. The world’s oceans, it turns out, function as what we call a carbon sink. Seawater naturally absorbs gases from the atmosphere, including carbon dioxide. In the early days of climate change studies, we thought this was a good thing. If the ocean was going to absorb around a third of that carbon dioxide, which it does, then that gives us a lot more time to solve the problem before climate change gets out of hand. And, to a certain extent that’s even true. But it comes at a cost: ocean acidification.

complex diagram of the marine carbon cycle
The marine carbon cycle is very simple and easy to understand.
Diagram by: E.L. Cavan, A. Belcher, A. Atkinson, S. L. Hill, S. Kawaguchi, S. McCormack, B. Meyer, S. Nicol, L. Ratnarajah, K. Schmidt, D. K. Steinberg, G. A. Tarling & P. W. Boyd, CC BY-SA 4.0 , via Wikimedia Commons

You know how that bully in high school had one or two other, lesser bullies that hung out with him all the time? They laughed at his mean jokes, agreed with everything he said, held you down while he stole your lunch money. This was ten thousand years ago, back when we used something called cash, of course, and you just kept money in your pocket instead of as ones and zeroes in a server somewhere. Anyway, those sidekicks kind of helped keep the bully in check. They entertained him. They served to make him feel important or strong, and were even an easy target for some of his frustrations or anger. He could assert his control over them, which kept him from bothering you so much. But there’s a tradeoff. Because of course, now there’s not just one bully but three, which is objectively worse. Plus, those sidekicks were probably a lot nastier when they were around him than they would have been if they’d been on their own. They drew off some of the lead bully’s negative emotions, but they were encouraged to have worse behavior as a result.

It’s the same damn thing with climate change and ocean acidification. Ocean acidification is the nasty sidekick that helps tone down the destructive tendencies of its boss, climate change. But now instead of having one villain to deal with, you have two. And if you keep your attention focused too much on the big guy, the sidekick could sneak around behind you, leap up on your back, screaming, and bite your ear while urinating all over you.

Err, unless that was monkeys that did that? I might be thinking of monkeys. Don’t fuck with monkeys, guys.

The Cliff’s Edge Chemistry Minute! Paragraph! Whatever!

We got off track there, but now it’s time for a segment we call The Cliff’s Edge Chemistry Minute! Alright, I’ll make it as painless as possible. Ocean acidification. When water absorbs carbon dioxide, it creates carbonic acid. This happens all the time and is a natural, normal process. The higher the concentration of carbon dioxide in the atmosphere, the more CO2 is absorbed by the ocean and the more acidic it gets. There are also various minerals present in seawater that can react with carbonic acid and neutralize it. Before the Industrial Revolution and the beginnings of massive fossil fuel use, the amount of acid created by absorbing CO2 wasn’t enough to alter the acidity, or pH, of the ocean, because minerals washed in from the land by rivers was enough to keep things in check. There was always some acid being created, and there was always some minerals being added to the oceans that reacted with the acids, and it balanced out.

That’s all changed now. The balance is out of whack. There’s more carbon dioxide in the air now, and so there’s more being absorbed by the seawater, which makes the water more acidic. The mineral input from freshwater sources, however, hasn’t increased. It’s no longer enough to neutralize the carbonic acid being created. The acidity is being increased quicker than it can be countered. The pH of the ocean used to be 8.2, which is slightly alkaline or basic. It is now 8.1, which doesn’t sound much lower. However, the pH scale is kind of weird, and little changes in pH actually indicate big swings in chemistry. That .1 drop in pH equals about a 30% increase in acidity. That’s significant. Significant enough that it’s starting to affect other minerals in the ocean that used to be stable. The main one being a little thing called calcium carbonate.

bottle of antacids, calcium carbonate
Gonna need a whole lot of this to fix the problem. Photo by Midnightcomm, CC BY-SA 3.0 , via Wikimedia Commons

Calcium carbonate might sound familiar to you, and it should. If you’ve ever had heartburn or an upset stomach and used an antacid, you were probably eating some calcium carbonate. So… just think about that for a minute. When you’re having trouble with your stomach acid, the quickest and easiest thing to do is to drop some calcium carbonate in it. It’s so good at reacting with acid that we call it an anti-acid or antacid. Okay. So here’s the problem. Calcium carbonate is also the main mineral in pretty much all seashells and coral skeletons. Clams, oysters, snails, and all hard corals all use calcium carbonate to build their hard bits. It’s also used by some kinds of algae and some plankton, which means lots of the little guys swimming around in the water that you can’t see or don’t notice. And if you giggled when I said “hard bits” just now, then you’re just immature and I’m very disappointed in you.

Better get your bone guy on the horn

The point is, turns out a lot of living things in the ocean are literally made out of antacid. So it shouldn’t be surprising to find out that adding acid to the ocean is bad for them. Before, at a pH of 8.2, these organisms were able to maintain their shells without much trouble. Some of the calcium carbonate might dissolve from acidity, but not quicker than they could grow new shell material. But now that we’re at 8.1, some species are already having trouble keeping up. Ocean acidification is causing their shells to dissolve as fast or faster than they can grow them. Imagine if your bones started becoming eroded on the ends or having little pits dissolved in them. You wouldn’t be happy. You would call your bone guy and have them take a look at you. And your bone guy would then say, “Yep, that’s just how life is going to be from now on. In fact, it’s probably going to get worse. You don’t really need all these bones, do you? Because the little ones are probably going to just go away.” And then you’d be so upset and scared that you’d forget to question what the hell a “bone guy” is and why you had one in your contacts list.

So, yeah, shelled creatures are not pleased with ocean acidification. It turns out that the ocean isn’t the same all over. Variations in temperature and current, combined with pollutants along coastal areas, mean that water chemistry varies a little bit between different sections of the ocean. So, some areas are more acidic than others right now, and they are giving us a window in to the near future. For instance, in the United States, coastal waters in the Pacific Northwest and New England are both more acidic than the ocean average. These areas are both home to important commercial fisheries, such as oysters and other shellfish. Adult oysters are doing okay in these areas. The acidity is affecting their ability to grow and maintain their shells, but they’re surviving. It’s taking more energy for them to grow their shells, however, and it takes longer. This means it takes longer for them to reach a harvestable size. But there’s a bigger problem.

oysters and scallops, species vulnerable to ocean acidification
Some of the critters who are already having trouble with ocean acidification in some areas

Larval oysters, also called “lil baby squirmy guys”, are basically just tiny blobs when they hatch from their eggs. One of the first things they have to do is to quickly grow a shell by pulling in calcium carbonate from the water around them. But in some of these areas with slightly worse acidity, they’re having trouble. There’s less calcium carbonate in the water because more is reacting with the carbonic acid. So it’s harder for them to grow their shells. If they can’t manage to grow one, they’ll die. If they grow a shell, but it takes so much of their energy that they have nothing left for growing their actual body, they’ll die. If they manage to pull it off and grow a shell and have a little energy left over, they may still be weakened enough that the first challenge they meet, the first stressful event, can be enough to do them in. Some commercial shellfish farms in these areas have had to start raising the pH in their water to keep from losing most of their young oysters. The wild populations, of course, aren’t so lucky. This problem will only get worse. As commercial shellfish operations can make up a big chunk of the local economy, this has the potential to have an immediate effect on humans as well.

Watch the seeps, peeps

Corals don’t like ocean acidification, either. Many corals use calcium carbonate to build their skeletons, and they’re having the same trouble building and maintaining these structures as the shellfish are. Even when they can build up their skeletons quicker than they are dissolved, it uses up more energy. That means less energy left over for other tasks like reproducing. Corals are getting screwed from two directions though, because they’re also sensitive to temperature change. Remember climate change? Yeah. Warmer water is stressful or even fatal for corals. Add increased acidity to that, and… it’s a grim view of the future. We don’t have to guess, either. There are places where there are natural carbon dioxide seeps in the ocean, and every once in a while there’s a seep in the middle of a coral reef. These natural sources of carbon dioxide do the same thing as the CO2 we pump in to the atmosphere. They make the surrounding water more acidic. They’re accidental acidification experiments for us to study. And what we see is, as you get closer to the seep, the thin, branched corals go away, leaving only the bulky, boulder-type corals. With a low enough pH, corals disappear altogether. I can’t tell you here how important coral reefs are to marine ecosystems. That’s just too big of a topic. For now, take my word for it: if coral reefs go away, life in the ocean will be dramatically changed forever.

Fish are going to be affected by ocean acidification as well. While their skeletons aren’t made of the same material as shells and so aren’t in any danger, a lower pH in the water means the body chemistry of the fish has to change as well. We don’t even know what all effects this will have, and it will likely affect different species in different ways. If nothing else, it will stress the fish by requiring them to spend more energy maintaining their own internal pH at optimal levels. Studies on clownfish have shown that lower pH makes them less likely to flee from predators and more likely to stray into more exposed areas. Other fish have shown changes in their “ear stones”, which are little structures in their head that sort of function like our ears and which are often, you guessed it, made of calcium carbonate. We’re just beginning to look at what this all means, so we can’t say how bad it is… but it’s a fair guess it won’t always be a good thing.

Series of photos showing a pteropod shell degrading dramatically when exposed to water mimicking predicted ocean conditions for the year 2100
Sequence of photos taken of a pteropod shell placed in water mimicking predicted ocean conditions in 2100. Top left is day 0, bottom right is day 45

Then there’s our good friends, the pteropods. You remember the pteropods, don’t you? We met them at the Johnson’s Christmas party a couple years back. Back before the plague, when we could still have parties. Well, that’s okay, just pretend like you remember them, they won’t know the difference. Also called “sea butterflies”, pteropods are basically little bitty marine snails, only instead of crawling around in the sand and on rocks, they actually swim around in the water. They are an important part of the marine food web, and some varieties have little shells just like normal snails. The shelled varieties are already having trouble with ocean acidification in some areas. Their shells are so small and thin, that just a little bit of material dissolving can wreck them. Or they have trouble forming them to begin with. If any species start going extinct due to ocean acidification, pteropods might be the first to go. And in case you think that’s not a big deal, remember that the little guys swimming around in the water are usually food for bigger guys. In this case, young salmon in particular are known to love eating pteropods. They can make up as much as half of a youngster’s diet. I don’t have to tell you that salmon are kind of a big deal, do I? Ask an orca, they’ll tell you. Although, if they actually tell you, like in English… record that and send it to me, please. I can definitely make a podcast episode out of it.

Bright spots… or at least less dark

Ocean acidification isn’t all gloom and doom, though. There are little bits of hope to be found. For one thing, not all organisms appear to be harmed by lower ocean pH. Seagrass and some algae like it just fine. The extra carbon dioxide is actually good for them, and the increased acidity doesn’t seem to bother them much. Crustaceans like crabs and lobsters don’t seem to care much either. Their shells seem to actually get stronger with increased acidity, so for now at least, they get a pass on this one. Some corals have been shown to suffer from increased acidity at first, but to gradually be able to adapt to it and maintain their skeletons. So… not 100% bad news. Mostly bad, but not entirely.

The bit about the seagrass and algae is actually potentially really important. Because these plants absorb carbon dioxide directly from the water, they actually lower the acidity of the water around them. Not a lot, but it’s measurable. Furthermore, we already use seaweed as food and food additives, among other uses. So, some folks are looking in to the possibility of farming this stuff at large scales. It could be both a way to sequester, or remove, carbon dioxide, and a way to reduce ocean acidity. Granted, it seems unlikely that we’ll be able to grow so much seagrass and algae that we raise the ocean’s pH back to 8.2, but it might be enough to improve the quality of the local waters near coastlines, where a lot of commercially and ecologically valuable species live.

Woman holding harvested seaweed
Some of the seaweed you’re gonna start farming for me. Photo by Rachel Clara Reed, CC BY-SA 4.0, via Wikimedia Commons

The bad news, though, is that the real solution for ocean acidification is the same as for climate change. Both the supervillain and the evil sidekick get their power from the same source: carbon dioxide emissions. And we know that that’s a huge challenge, because in a way, we’ve based our entire economy on producing CO2. It’s going to be hard to switch away from that, and there’s powerful forces working to maintain the status quo. But the good news is, we at least know what we need to do. Reduce our carbon footprints. Not just for individuals like you and me, but for our communities, for industries, for entire nations. Get rid of fossil fuels and replace them with clean and renewable energy. Push and push and scream and yell and demand our leaders take action. Only now, you’ll be armed with one more fact. You’ll be able to tell them that unless we stop carbon emissions, we’re not only fucking up the atmosphere, but the oceans, too.

If that sounds like too much work for you, then might I suggest starting a massive seaweed farm? While you’re out doing that, if you see the Pteropods, tell them we can’t be at their dinner party next week, because there’s still a fucking pandemic going on and it’s not cool to do parties right now. Just make sure you do it when their monkey’s not around. He’s really been looking forward to that party, and believe me, you do NOT want to piss him off.

Woods Hole
What is ocean acidification?

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