One thing I love about my job is that great footage is often a short drive away, or in my own yard. Tallahassee is surrounded by hundreds of thousands of acres of the Apalachicola National Forest, St. Marks National Wildlife Refuge, numerous state parks and state forests, Wildlife Management Areas, and more than a couple quality rivers, lakes, and wetland areas. Or I could just head out into the backyard habitat and photograph any number of plant and insect interactions. It’s crazy how much you can see when you slow down and take a look.
Another thing I love about my job is when I get to have a little adventure, and dig into a larger story. The recently completed WFSU Ecology documentary, Secrets of the Seep, featured ecosystems that I may never get to visit in person. I don’t have the ability to visit repeatedly, in different seasons, early morning or maybe overnight. I won’t see surprise animals, or animals doing surprising things.
That’s the nature of studying the deep ocean floor. Researchers have to plan for years before heading out to sea. They don’t have the luxury of roaming aimlessly and observing, taking a moment to follow a critter they’ve never seen before. They go with an objective, and they go with the knowledge that conditions may not always allow for a safe passage to the study site.
In Secrets of the Seep, we spent a week-and-a-half off the coast of Oregon studying methane seeps. Geology and chemistry meet ecology, as microbes convert methane into dissolved organic carbon, fueling a deep sea food web. The research focused on the microbes and on chemical processes, but I am above all else an ecology guy. What eats dissolved organic carbon? How far away does it drift from methane seeps? How connected is an ecosystem 800 meters deep to the rest of the ocean? Is it connected to fish we eat?
And what else is going on at the bottom of the sea?
Meet three guests who have visited the ocean floor
- Dr. Ellen Lalk, Stable Isotope Biogeochemist, US Geological Survey/ Woods Hole Campus
- Dr. Karen Lloyd, Wrigley Chair in Environmental Studies and Professor of Earth Sciences and Marine and Environmental Biology , University of Southern California
- Dr. Amy Baco-Taylor, Professor of Oceanography and Environmental Science at Florida State University
Ellen and Karen star in Secrets of the Seep; they are members of the SeepDOM team. Karen studies microbes living in ocean sediments, and below ground. Ellen is focused on the processes that create dissolved organic carbon (DOC), and whether that DOC can be consumed by other organisms.
Their work is grounded in the microscopic, and I wanted to know more about the animals we can see with the naked eye. That’s Amy’s area of study.
All three guests are members of an exclusive club. All three have visited the ocean floor in the Alvin submersible. Alvin is also a star of Secrets of the Seep. It’s a research submersible owned by the U.S. Navy and operated by Woods Hole Oceanographic Institution. It has been in operation for over 60 years, during which it has been used to discover the wreckage of the titanic, and two of the phenomena we discuss in this podcast: methane seeps and hydrothermal vents.
We start by heading down in the Alvin…
Coast to Canopy blog posts are curated transcripts. My notes appear in italics.
Down through a spectrum of blue.
Amy Baco-Taylor: Usually where you do an Alvin dive, you start out in blue water… It’s all blue water. So the biggest thing you notice is a drastic change in the wavelengths of light that you see. It goes from bright daylight through different shades of blue, like shades of blue that you’ve never seen before. Really beautiful shades of blue. And then it gets darker and darker, and eventually there’s no ambient light, and you start to see bioluminescence.
What does it look like when you reach the bottom?
Rob Diaz de Villegas: Once you’re closer to the sea bottom, towards the edge of the continental shelf… On this cruise where [the SeepDOM team was] looking for methane seeps, what kinds of things did you see when you were down, off the coast of Oregon?
Ellen Lalk: As we get closer to the seafloor, and it starts to come into view, the first thing that we saw was hundreds of pink starfish scattered around the soft, light brown sediment. And from that point, started hunting for methane, signs of methane seeps.
While we’re searching, we found that when we get to patches of the seafloor where the sediment turns from that light brown color to black, with patches of white microbes. And if you look in the right place, you might even see some things, like bubbles escaping into the water column, or some mineral formation.
Rob Diaz de Villegas: What are some other sort of features we might see on the seafloor? Things like hydrothermal vents? Mud volcanoes? Brine lakes?
Karen Lloyd: I’ve dived on those different formations and I can speak to that a little bit.
There’s different geological features that drive these different seafloor features. But a lot of them are also associated with methane and gases coming up. So you often see very similar shrimp and crabs and worms, no matter what the geological sources.
That can affect the temperature of the fluids coming out, which can affect what animals you see. But, pretty much all of these places at the seafloor are like oases in the desert where you find lots of abundant life.
Whale falls: a buffet for the bottom dwellers
To prepare for the interview, I read a paper Amy co-authored, about methane seeps, hydrothermal vents, and other chemically driven ecosystems on the ocean floor. The paper also discussed food sources that dropped down rom the upper ocean.
Amy Baco-Taylor: When a whale dies, its body often sinks to the seafloor. We think about them washing up on beaches, but actually, they all eventually end up on the seafloor. And so, once the whale reaches the seafloor, then there’s this huge amount of organic material, food on the seafloor… the deep sea usually doesn’t get a lot of food from the surface.
So there’s this huge buffet of whale flesh for all of these organisms to feed on. The initial community that you see on the whale falls includes a broad array of different scavenging species. So, there’ll be large sharks.
And one of the more common species that feeds on the whale soft tissue are hagfish. There’ll be literally thousands of hagfish swarming all over the whale… they actually eat the whale from the inside out. They find a hole and go inside and eat the flesh…. it’s really a pleasant way to go, I guess.
And then, as there gets to be less soft tissue, the scavengers get smaller. So, you might see thousands of amphipods in big swarms, feeding on the soft tissue.
And then there’s also all kinds of organisms that live in the sediments, feeding on all of that organic material as it rots.
When the whale meat is gone, chemosynthesis happens
Rob Diaz de Villegas: And then some of them are what you’d call chemosynthetic organisms. They’re towards the end of the of the decomposition of the whale.
Amy Baco-Taylor: Yeah. So once all the, tissue is removed, the soft tissue, the bones actually contain a very high concentration of lipids, or fats… because it’s trapped inside the bones, it gets broken down really slowly through microbial processes. And just like anything that rots, you get that hydrogen sulfide smell.
And so it creates this hydrogen sulfide, which then fuels the chemosynthetic community on the whale falls for a period of time, and also in areas in the sediments where a lot of the soft tissue gets trapped, they can also form in those areas for short periods of time as well.
Chemosynthesis is the chemical version of photosynthesis. In photosynthesis, plants use the energy of sunlight to power process of taking water and carbon from the atmosphere to create carbohydrates, which they use to build their bodies. In the absence of sunlight, deep sea microbes use chemosynthesis, consuming methane and other chemicals, and often excreting carbon in forms that other organisms can eat: dissolved organic carbon.
To borrow a quote from my blog post for Secrets of the Seep, “Dissolved organic carbon is the largest reservoir of organic matter in the ocean,” says Dr. John Pohlman, research chemist with the US Geological Survey, and a Principal Investigator for the SeepDOM project.
Dissolved Organic Carbon/ Matter | DOC & DOM
Ellen Lalk: When I think about organic matter in the ocean on a larger scale, we can think of animals like whales or dolphins, plants like seagrass or microorganisms like algae that can form things like red tides. And all of these living things take carbon from their environments to grow and also excrete carbon back into their environment as waste, just at different scales.
So at the base of this food web, meaning at this microbial level, the carbon that’s getting taken and excreted is so small that it’s, it’s actually in a solid form… these are really, really small organic molecules.
And DOC… which is dissolved organic carbon, is an incredibly diverse mixture of different compounds. These are molecules that are coming from life itself. So it can involve things like carbohydrates, sugars- it’s incredibly complex. And some of the chemicals in dissolved organic carbon in the ocean are more accessible to microbes than others.
I’ll refer again to the blog post for the documentary, where we delve into this chemistry with more detail. Essentially, microbes take methane and other, often toxic, chemicals at the sea floor, and break apart the molecules. They then output different molecules, including various forms of DOC.
Microbes make food from methane
Ellen Lalk: Up to 90% of methane that migrates to the seafloor, at seeps, is consumed by microbes. And once you get that methane into the water column, it becomes a lot easier to oxidize that methane. So, when you look at waters at the surface of the ocean are above methane seeps, there’s not a very strong signal in that water of methane making it to the atmosphere, because there’s so much microbial processing that happens in the deep ocean around those methane seeps.
Ellen mentions the oxidation of methane. The oxygen required for that process comes from water, or molecules of other substances, such as sulfate.
Karen Lloyd: One way to understand that processing that Ellen’s talking about is that we use natural gas to heat our houses. And so what’s the reaction? The chemical reaction that makes fuel for things like heating your house is methane burning with oxygen. And it’s weird to think about things burning in the ocean, because the oceans are wet.
So, you’re not going to light a match down there. But chemically, it’s the same process. It’s oxygen and methane reacting with each other, and in the same way that it creates a ton of energy up at the surface when we when we use it, it also creates a lot of energy in the bottom of the ocean.
That’s a great thing. We should be really happy about that. Because if that weren’t burning off the methane, then it would be getting into the atmosphere, and we would be in real trouble.
Ellen Lalk: When I think of the processing of methane in shallow sediments and also in the deep ocean, I think of it like a chemical currency… They can either put this carbon into their piggy bank and use it to grow themselves, or they can modify it and exchange this carbon, and send it back out into the environment.
These chemical exchanges are how microbes convert methane into things like dissolved organic carbon, which is a major focus of the work that we were doing out offshore Oregon.
What lives in the boring places between ocean oases?
If seeps and hydrothermal vents are the oases, what lives between them?
Karen Lloyd: We’re talking about these methane oases. So, if you have oases, that means the rest of it is desert, right? To have an oasis means the rest of it is kind of boring. For years, I sort of naturally gravitated to this boring place, just because it’s common. The vast majority of Earth’s surface is covered by oceans, and the vast majority of the mud underneath our oceans is mud that doesn’t have a methane seep. It doesn’t have anything really interesting going on with it at all.
And I’ve got some colleagues who’ve done a really great job estimating the total number of living microbial cells in this sort of boring ocean mud. And it’s like 1029 living cells, which is like a hard number to really conceptualize in your brain (it’s ten followed by 29 zeroes). It’s 10,000 times more than the number of stars in the universe. Not the galaxy, but the universe… it’s a lot.
So, even though it doesn’t seem like there’s much going on in those places, it’s a real ecosystem, and they’re doing some interesting things.
There’s more than microbes in the “boring” ocean mud
Amy Baco-Taylor: I think that a lot of the soft sediment areas that are around cold seeps…They look like deserts to your naked eye. But what’s actually happening is that instead of living on the surface where you can see everything, most of the organisms live in the sediments.
If you could actually take samples of the sediments and look at those under the microscope, you would see that there’s actually a huge diversity of very small organisms that live within the sediments. There’s still tons of life there. It’s just not out in the open where you can see it.
Rob Diaz de Villegas: What what kinds of organisms are we talking about?
Amy Baco-Taylor: Largely, polycheate worms are the most common groups that you find there, but there’s also a lot of crustaceans and a whole suite of invertebrate taxa.
Rob Diaz de Villegas: These are all just in the mud?
Amy Baco-Taylor: Yeah. They live within the mud. Some of them burrow and dig within the mud. We call those size class of organisms macrofauna. And then there’s even smaller organisms that we call meiofauna that actually live there, so small they can live in between the grains of sand or sediment on the seafloor.
Rob Diaz de Villegas: What are they eating down there?
Amy Baco-Taylor: The smallest ones are eating microbes. The meiofauna usually eat microbes, and sometimes each other. And then the macrofauna eat the meiofauna. Then we have larger organisms that we call megafauna. And they will come along and, you know, burrow in the sediments and eat the macrofauna on meiofauna.
Sometimes, microbes team up with animals to convert methane
When the SeepDOM team searched for seeps on the sea floor, one sign they looked for were beds of bivalves. mussels such as Acharax have a relationship with chemosynthetic microbes, and are often found by methane seeps.
Amy Baco-Taylor: There’s microbes living symbiotically within the bodies of large organisms. They produce organic carbon that the host organism absorbs directly from the microbe. And they get their nutrition that way. It’s like a symbiotic relationship where the host organism gives the microbe a place to live and supplies some of the sulfide and other compounds that the microbes need.
Then, in return, the microbes give the organisms the organic carbon that they need.
Karen Lloyd: Most of these invertebrates that you find at methane seeps, if you start looking inside their gills, you find symbiotic chemosynthetic organisms.
Tubeworms
So far, we’ve been talking about methane seeps in the north Pacific Ocean. Methane seeps are found worldwide, and were first discovered off Florida’s Gulf coast. Here, we find animals we don’t find off the coast of Oregon, such as-
Amy Baco-Taylor: Tubeworms. Most people, I guess the easiest analogy of those… if you watch any type of nature special, they usually show these really long red tube worms that occur at hydrothermal vents. They’re very bright red with a white rim around them. And they’re sticking out of white tubes and they’re very photogenic. So you often see pictures like that.
So the ones that we find it cold seeps are very closely related to that, but not nearly as photogenic. They’re usually a bit smaller and have slower growth rates than the ones that you find at hydrothermal vents.
For a long time, we thought that tubeworms were their own phylum. And we figured out through genetic work that they’re actually a type of polycheate worm. They’re just super-highly evolved and specialized to the chemosynthetic ecosystems… they don’t have… chaetae (bristles typical of polychaete worms)… like other polycheates have, but they also have no gut. They’ve developed this specialized organ inside their body called a trophosome.
And in their trophosome, they house these chemoautotrophic bacteria. And they also have specialized physiology where they can absorb hydrogen sulfide from the water and bring it to the bacteria.
Hydrogen sulfide is usually toxic for most organisms. So this is a pretty highly specialized adaptation. And then, the microbes give the tubeworms organic carbon compounds in return.
[Microbes] provide all the nutrition for the tubeworm in exchange for the tubeworm giving them a house and bringing in that hydrogen sulfide for them.
What eat mussels and tubeworms at methane seeps?
Amy Baco-Taylor: Because they live in these settings where there’s high concentrations of methane and hydrogen sulfide, which, again, are toxic to most organisms that haven’t developed these adaptations, there’s not a ton of predators that live directly within the chemosynthetic ecosystem. There are a few different types of crabs that will take little pinches off of these organisms. And if an organism dies, there’s scavengers that will come in and take tissue from the dying organisms.
But I would say that the number and type of predators that you find in these ecosystems is much lower than outside of the ecosystems, because the chemistry in the area, the high concentrations of these toxic compounds.
How far does the chemosynthetic food web spread?
Methane in the sea floor is an enormous carbon sink. Not one knows precisely how much methane escapes the sea floor through seeps and vents, but it is likely a significant amount. Surely methane-derived carbon feeds more than tubeworms and mussels…
Amy Baco-Taylor: I think that’s one of the big questions in chemosynthetic ecosystem research right now is, what is the sphere of influence of these chemosynthetic ecosystems out into the broader community? We suspect that it is significant, but it hasn’t been fully quantified yet.
There’s several potential ways [it can spread out into the ocean], besides the DOC and scavengers and predators that come into the ecosystem. There’s also all of the larger invertebrates that live with the ecosystem. [They] release their young; they spawn their larvae and eggs and sperm and everything into the water column. And so that is one potential way that the organic carbon produced at the seep is released into the other areas in the form of, the babies, basically.
Then, anything that lives around there can capture those larvae and that would be a food source for them.
The others can explain better the microbial side of it.
Karen Lloyd: I want to know that answer. I’d love to know how much of the carbon that we appreciate on the surface of Earth comes from chemosynthesis. You know, it’s something that is often ignored because we have this dominant signal of photosynthesis up at the surface, and certainly [chemosythesis is] not going to be anywhere near as much. We know that.
But, if it just stopped, if you snuffed out the chemosynthetic engine inside Earth one day, would that affect us? Would we even notice?
Potential food web clue: sablefish visit methane seeps
In one scene from Secrets of the Seep, an Alvin dive is harassed by a school of sablefish. Also known as black cod, this is a commercially fished species that spends most of its time higher up in the ocean. Researchers don’t know why they visit the deeper ocean, or what they eat there. But this animal is common near methane seeps. What do they eat when they’re down there?
Karen Lloyd: Can I talk about the fish?
Rob Diaz de Villegas: Yes.
Karen Lloyd: I was thinking this was either a horror podcast, now that we’re bringing up the fish, or drama. But now I realize it’s therapy. So these fish… the weird thing is, you know, we’ve all dived in submarines and you use these – sorry, submersibles. If it has a support boat, you call it a submersible.
Usually, you’re deep enough down that you’re not getting very active, energetic organisms. Things are slow. The fish will will move quickly if they get scared. But, generally speaking, things are pretty stable and everybody’s peaceful, and you do your work and you all agree. The animals and you have a nice conversation and you end up with science.
This situation was something that I had never seen before. And the pilot, who has done far more dives than I had, had never seen before.
These sablefish are sport fish and they’re very energetic… and they were attracted to the submersible, maybe because of the light. We would settle somewhere and try to start working and they would start swimming around us in this big like ball, maybe 50 fish, 50 of these big fish.
And as they did that, they would go through the sediments around us. They would kick up en masse like a big giant poof. All these sediments would cloud our vision. And so we had maybe five minutes after we would land in a place to do any work until we lost all visibility and we couldn’t even see the robotic arm.
Do sablefish bring chemosynthetic carbon into the greater ocean?
Karen Lloyd: And I’d never seen that happen before. But that’s interesting, Rob, I didn’t think about the fact that these big energetic fish- what were they doing at 800m water depth? They shouldn’t be that low. And I did look up later and I saw that they are known to go that deep. That’s not a discovery that we made.
But why? All the good stuff is up in the surface. That’s where all the jellyfish are. That’s where all the the little fish that they eat. I’m sorry. I’m not an organismal biologist. So there’s probably smarter ways to say that, but, maybe they are part of that deep sea ecosystem.
Maybe they are how some of that carbon from chemosynthesis is getting out into the surface world.
Why haven’t humans seen more of the sea floor? Because it’s hard to go there.
Karen Lloyd: What you really asked me to say is, why this is hard to study? And part of it is that things like that happen. That’s one dive that could have been nine hours, but we cut it short because the fish were just useless and we couldn’t do anything down there.
And I think also the weather was starting to get a little rocky up at the surface too. So if that’s how you access your study site, compare that to somebody studying a forest. You can live in the forest. You can talk to the the groups of people who have been living in the forest for thousands of years.
The amount of information that we can get just just for walking up to a place, or reading a book from people who’ve lived there, at the surface… None of that applies in the bottom of the ocean. It’s just, it’s an alien landscape.
Rob Diaz de Villegas: Yeah.
Karen Lloyd: Again, I say just to finish my therapy thing, even even though we had basically very little science happen on that dive, I was still happy and thrilled and pleased to be able to get to dive, because it’s so rare to get to have that even though it was a terrible dive. I’m so grateful to have gone to the seafloor yet again.
The thrill (and practicality) of going down in the Alvin
Ellen Lalk: I think we have personal reasons why we like seeing these sites in person, but also logistical, scientific reasons why we need to see these sites in person.
Personally, I think I mentioned in the documentary, it is a big scientific dream of mine to be able to do something like dive in the Alvin and make that connection with an environment that I spent a lot of my life studying.
Logistically, being able to go down, see the site in person and make realtime decisions about where we’re taking samples from, get the full scope of the environment from where we can see it inside the submersible, and take really precise samples is why we do it.
I know you were asking about what goes into being able to study these types of environments. And what I was thinking about was, in the moment when I’m down there, I feel like an explorer. But the truth of the matter is, by the time that I’m at the seafloor in the sub, years and years of work have gone into probing that site from a distance, making pretty detailed maps, testing all sorts of hypotheses that we use to develop a strategy for why we ought to go to a particular part of the world.
I felt by the time that opportunity came up, not really fear, but just excitement and a really deep sense of duty, of the responsibility of making decisions on behalf of an entire team, especially in light of our trouble with weather and getting a lot fewer dives than we thought we were going to get.
The weight of thinking through the choices that I’ll have to make to help other scientists on our team get samples to do good work. And also the years and years of planning, of other members of our team in the scientific community, towards getting the ship time and the dive time, to take those samples.
Why a submersible is more effective at sampling than a Remotely Operated Vehicle (ROV)
Amy Baco-Taylor: I think one of the benefits of going there in person is that you get a really much better sense of the three dimensional layout of an ecosystem.
When you go down in a submersible, you’re looking at a window, and so you can see sort of everything and how things are in relation to each other. And some of the interactions that are going on are very different from the experience of using an ROV, where you just have a camera that’s looking in a finite area at what’s going on.
It’s the difference between seeing someplace you want to go on vacation, right? You see it on TV, and you know that it’s beautiful and you know that it’s interesting. Right? But you can’t go and tell people, oh, like, you know, I saw the Eiffel Tower on TV, so I don’t need to go see it in person.
Right?
You want to go there and see it in person, and you go there and you see it in person and you realize not only is there an Eiffel Tower, but there’s all these people walking around the Eiffel Tower and there’s vendors there, and there’s cool food over here, and there’s all these other different things happening besides just the tower.
When you go down in a submersible, you really get a much better sense of all those different things that are happening. Whereas using an ROV is more like just watching it on TV.
Another advantage of submersibles is that there’s much more maneuverable than other types of vehicles. And so if you’re going along and you see something that you want to sample, you can like stop on a dime and just go there and sample it.
Whereas with using an ROV, it’s connected to a ship. And sometimes it also has a drop weight between the ROV and the ship. And so if you want to stop and sample something, you have to stop the ROV and the drop weight and the ship. And by the time you’ve done all those things, you’ve drifted way past whatever you wanted to study, and it’s harder to get back to it.
Karen has a new book!
Karen Lloyd: I have a book coming out May 13th… Actually, this relates to this cruise because I was basically talking about it the whole time I was on the cruise and various folks on the boat gave me input and advice about it. It was really a labor of love. And I basically just talk about what it’s like to do this exciting field work.
Then I go to get into the nitty gritty of the science as well. So hopefully people will enjoy it. It’s called Intraterrestrials: Discovering the Strangest Life on Earth, from Princeton University Press.
Ellen’s closing thought
Ellen Lalk: I think that it’s profoundly humbling to be face to face with the fragility of some of these environments that are often untouched frontiers. And, each dive that we get to do represents an opportunity to shed a little bit of light on some of the unknowns of our planet.
The documentary that you produced, I think, captures really beautifully the experience and the motivation for doing this work.
On that note, have you watched Secrets of the Seep yet? Here is the link again!
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