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Oceans have always done us a favor, absorbing carbon dioxide in the atmosphere. But now rising greenhouse gases are warming the ocean and changing its chemistry. All of this is putting marine species and ecosystems at risk, threatening food security and the livelihoods of people along its shores. In this episode of Unfold, we’ll take a deep dive into the ocean to examine the effects of climate change.

In this episode:

Priya Shukla, Ph.D. student at Bodega Marine Laboratory, Department of Environmental Science and Policy

Tessa Hill, professor and oceanographer, Bodega Marine Laboratory.

Episode transcript

Amy Quinton: It's low tide on Tomales Bay in Marin County. The bay touches the Pacific Ocean, but I'm on the southern end where the Tomales Bay Oyster Company raises and harvests its oysters. I'm following Priya Shukla, a graduate student at the UC Davis Bodega Marine Lab who stops when she sees something moving in the estuary. 

Priya Shukla: Those are bat rays, Amy. I've never seen them frolicking before as the tide goes. 

Amy Quinton: Out in the bay, bat-like fins from two rays flap on the surface of the water. 

Priya Shukla: There's an eelgrass bed right here. You can see like all bit of bubbles at the surface tight just off the shore here. They like to eat all the clams. He's still going. Go, buddy. 

Amy Quinton: Priya didn't come here to admire the bat rays. Although we both stopped to watch them for quite some time. She came here to inspect her oysters. She picks up a two by three-foot plastic mesh bag from the edge of the bay. 

Priya Shukla: It's essentially like a mesh envelope. And so inside of it are currently 250 oysters. And so the plan is that I'm going to go and check on the oysters and see how many of them have survived and how many of them have died. And I know they’re dead because they're not closed they'll be open. 

Amy Quinton: Priya expects some of them to die. When the water in Tomales Bay warms in the summer, it makes these quarter-sized oysters susceptible to a particularly deadly virus called the oyster herpes virus. 

Priya Shukla: In Tomales Bay, we see a mortality rate of about 50 percent, so 30 to 40 percent, up to 50 percent. But in other parts of the world, like France and Australia and New Zealand, it can kill close to 100 percent of the entire oyster stock. So understanding how this affects the Pacific oyster which is what we have here is really important because this is actually the most commonly farmed oyster across the entire world. 

Amy Quinton: Priya says the temperature in Tomales Bay has warmed gradually over the last decade as climate change warms the ocean. It's putting not just oysters at risk, but all kinds of marine species and ecosystems. Climate change is also changing the chemistry of the ocean water and all of that is threatening food security and the livelihoods of people along its shore. In this episode of Unfold, we'll take a deep dive into the ocean to examine the effects of climate change. 

Theme: Climate models all agree that temperatures are going to increase. It's going to be hotter. It's going to be drier. Fires are going to burn more frequently. Maybe this is never gonna be the way it was again. We need to come up with ways to literally pull CO2 out of the atmosphere. How are we going to work together to solve a challenge like climate change? 

Amy Quinton: Coming to you from our closet studios as we shelter in place across the Sacramento region, this is Unfold, a UC Davis podcast that breaks down complicated problems and discusses solutions. This week, we unfold oceans in a changing climate. I'm Amy Quinton. 

Kat Kerlin: And I'm Kat Kerlin. 

Amy Quinton: Hey, Kat, I got to tell you, I'm super excited to talk about the ocean. I grew up in the South and spent what seems like every summer escaping to the Gulf Coast, swimming and snorkeling in the warm waters, watching shrimp boats head out and eating oysters on the half shell, which is another reason I'm super excited to talk about Priya's research. 

Kat Kerlin: Yeah, I love the ocean, too. It's so peaceful and invigorating all at once. And it's full of all these mysteries underwater like bat rays. But I have to say, I am really worried about the ocean. It's in a lot of trouble thanks to climate change and just general environmental degradation. 

Amy Quinton: And even if you don't live near an ocean or even think about it too often, I think many of us understand its importance. If for no other reason, the ocean provides a source of food for billions of people. 

Kat Kerlin: It's good to talk to Priya then, since she's researching sustainable aquaculture. 

Amy Quinton: And like she said, the most commonly farmed oyster is really susceptible to disease when the oceans warm. 

Kat Kerlin: And we all know the ocean has been warming. 

Amy Quinton: Yeah. I also talk to Tessa Hill about that very thing. 

Kat Kerlin: She's a professor in our Earth and Planetary Sciences Department and also with our Coastal and Marine Sciences Institute. She says the changes in the ocean that we're seeing as a result of climate change are alarming. 

Tessa Hill: We observe things happening in the ocean today that are fairly remarkable. We observe, you know, warmer temperatures than what have been recorded in the past, or we observe these very large heatwave events where we see unprecedented blobs of warm water up and down the coast that we don't really have a record of occurring before. 

Kat Kerlin: The big blob. I remember that. That happened off the California coast when we were also experiencing a major drought. It basically cooked the ocean. It affected all sorts of marine life, from whales and seabirds to crabs and sea stars. 

Amy Quinton: And oysters are really sensitive to changes in the ocean because unlike fish, that could move to cooler spots. Oysters are well stuck, particularly if we're talking about aquaculture. So here's where Priya's research comes into play. She wondered, can we make an oyster that can tolerate warming ocean temperatures? 

Amy Quinton: On the shores of Tomales Bay, Priya Shukla pours 250 small oysters onto a tray. 

Priya Shukla: I'm gonna count how many are alive and how many are dead. And that's so that we can measure cumulative mortality, how many are dying over the course of the entire deployment between July and October. 

Priya Shukla: And then we're gonna take them back to the lab and look at their gill tissue as well as their mantels. The mantel is what produces the oyster shell and see if we can actually capture how much herpes virus there is in those tissues. And then that will give us a sense for what the frequency of the virus is in the Tomales Bay environment overall. 

Amy Quinton: Priya is counting her oysters here at Tomasini Point at the southern end of the estuary. But she also samples oysters by the mouth of the estuary where it hits the Pacific Ocean and the water is much colder. 

Priya Shukla: What I'm trying to look at is if there is in fact a difference in the frequency of the virus or the intensity of the virus when you're looking at these cold versus warm sites. 

Amy Quinton: She says typically, when temperatures exceed 60 degrees Fahrenheit, that's often when these young oysters get the virus. 

Priya Shukla: To put the temperature in context, 60 degrees Fahrenheit is when we see this virus outbreak. The average temperature of San Francisco is 63 degrees Fahrenheit. But for these oysters, that is considered warm. So this idea that we are trying to keep ourselves within a two degrees Celsius envelope globally, it's very similar for the oysters that it's just a small increase in temperature can have a really large effect. 

Amy Quinton: With a warming ocean, conditions are ripe for viruses to kill oysters. But Priya wants to see if humans can play a role in helping the oysters survive despite the temperature increase. 

Priya Shukla: We can capture the patterns of mortality at these different leases, can we then find a way to grow oysters in the lab that make them more temperature tolerant? So perhaps we can actually find a way to create temperature-resistant oysters or temperature-tolerant oysters. 

Amy Quinton: That's the hope. But oysters and other marine organisms face more than just warming temperatures as a result of climate change, which we'll unfold next. 

Amy Quinton: Hey, Kat, I don't want to dwell on the oyster too much, but it's one of those marine creatures that's really facing a lot of obstacles under a changing climate. 

Kat Kerlin: Obstacles? You mean like oyster drills? 

Amy Quinton: Oh, yeah. I saw those when I was out there at Tomales Bay with Priya. I also saw poisonous oak, mosquitoes and ticks, but that's another story. Do go on. 

Kat Kerlin: So oyster drills are these predatory, invasive snails that literally drill holes into an oyster shell and slowly kill it. One of our researchers here found that under a changing climate, those little suckers may thrive. And it's not just warming temperatures that allow the drills to thrive. It's ocean acidification that's making the oyster weak. 

Amy Quinton: Tessa says so much of that carbon dioxide that humans are releasing into the atmosphere ends up in the ocean. 

Tessa Hill: And the ocean is a tremendous sponge for that carbon dioxide. So it actually soaks up about 30 percent of what we put in the atmosphere goes straight into the ocean. And so we used to think about this as, wow, the ocean is doing such a great favor for us, right? Like, it seems like it's taking carbon out of the atmosphere that would have produced even more climate change. And it's being stored in the ocean instead. And then over time, we realized that adding all of that carbon dioxide to the ocean fundamentally changes the chemistry of the ocean. It makes it very slightly but measurably more acidic. 

Kat Kerlin: Lots of sea creatures are used to a certain pH and have evolved to live in that environment. 

Amy Quinton: Tessa explained that's especially so for shellfish. 

Tessa Hill: So anything that makes a hard part, like a coral reef or an oyster or a mussel, it's basically pulling the components of that shell out of seawater. And so it's making that shell from building blocks in the seawater. And it turns out that how abundant those building blocks are is dependent upon the pH of the ocean. 

Amy Quinton: So, again, bad news for the oyster. 

Tessa Hill: I think you could see a future possibility of both smaller animals and animals with weaker shells, meaning they're more susceptible to maybe a predator that comes along trying to crush their shell or drill through their shell. They might be more susceptible also to just the harsh environmental conditions of the ocean. The ocean is not that easy of a place to live. And so that shell is pretty important. 

Kat Kerlin: But, Amy, it's not just shellfish or oysters that are susceptible to a more acidic ocean. Our researchers have found that ocean acidification is reshaping the relationship between predator and prey. And that could really disturb the food chain. 

Amy Quinton: Yeah. Tessa told me about this. Are you talking about the snails and sea stars? 

Kat Kerlin: Yeah. So researchers at the Bodega Marine Lab collected ochre stars and black turban snails. Both are really common along the coast. They looked at their interactions under 16 different levels of acidity, including those conditions expected by the end of the century. 

Amy Quinton: And sea stars are the snail’s predator, right? 

Kat Kerlin: That's right. And they found that the more acidic the seawater, the more it impaired the snails escape response. 

Amy Quinton: So the snails are just like, I'm going to hang here in the tide pool and eat while they should be running away? 

Kat Kerlin: Exactly. And you can read about that study on our science and climate website at climatechange.ucdavis.edu. 

Amy Quinton: Again, nice plug, Kat. I would think for people who aren't studying what's happening in the ocean, all of these changes might seem pretty hidden. But Tessa told me lots of people who rely on the ocean for their livelihood are seeing these changes firsthand. And they're happening really fast. 

Tessa Hill: And if you talk to fishermen or oyster farmers, for example, what you will hear is that they can tell you many, many stories about how things have changed so rapidly in the past 10 to 15 years. So it worries me that our action is not yet meeting the urgency of the problem. 

Amy Quinton: Tessa partners with Hog Island Oyster Company as an example. The business is having to adapt to these changes. 

Tessa Hill: They're having to think about, you know, new places to raise their oysters or maybe even new varieties or genetic strains of oysters that they would raise that will be better adapted to these future conditions. I think the challenge with climate change and ocean acidification is that we're dealing with so many different changing parameters all at the same time. So it's not simply a matter of like, you know, dialing in the oyster strain that does really well under, you know, a temperature and a PH because we're seeing the ocean change in so many fundamental ways all at the same time. 

Amy Quinton: But Kat she says we're learning a lot and is hopeful about being able to sustain the oyster in the future. 

Kat Kerlin: Well, thinking about the future. There are things that we can do to help the ocean under a changing climate. 

Amy Quinton: You're talking about blue carbon, right? We should probably explain that blue carbon is the carbon that is stored in coastal and marine ecosystems like mangroves and tidal marshes and seagrass. 

Kat Kerlin: And even kelp. So just like you can sequester carbon in trees or forests and soil and grasslands, you can also sequester carbon in these marine ecosystems. Seagrass, for example, covers less than 0.2 percent of the ocean floor, but it stores about 10 percent of the carbon. So areas like these are really important to conserve. 

Amy Quinton: Yeah and Tessa told me that seagrass can change the water's chemistry as well. 

Tessa Hill: They locally modify the chemistry. They essentially buffer the water by removing the carbon dioxide. And so you can get a little around that patch of seagrass. You can get an area where ocean acidification is less of a problem. 

Amy Quinton: And she says the sediments around seagrass can store more carbon than the surrounding estuary and store it for hundreds of years. 

Tessa Hill: It's not the kind of solution that will solve our problems with climate change and ocean acidification. But what it can do is sort of help or mitigate those effects on a local scale. 

Kat Kerlin: And seagrass has all sorts of other environmental benefits as well, like providing a lot of biodiversity. It's home for many important species. 

Amy Quinton: Tessa is working with the state of California to figure out how much carbon can be removed by preserving these seagrasses. It may then become a revenue source under California's cap and trade program, which is the state's greenhouse gas reduction program. 

Kat Kerlin: So I cannot believe we ended an episode on oceans and a changing climate on a positive note. 

Amy Quinton: Well, I could change that if you wanted. 

Kat Kerlin: No, don't. But you can find out more about Tessa Hill and her research at ucdavis.edu/unfold and more about our ocean research at climatechange.ucdavis.edu. I'm Kat Kerlin. 

Amy Quinton: And I'm Amy Quinton. Thanks for listening. 

Credits: Unfold is a production of UC Davis. It's produced by Cody Drabble. Original music for Unfold comes from UC Davis alumnus Damian Verrett and Curtis Jerome Haynes.