Episode 22: Sediment Secrets: What the Lagoon’s Tiniest Animals Are Teaching Us About Lagoon Health

Daniel Kolodny:

Infauna, are these sediment dwellers the key to unlocking IRL restoration? Today we will discuss benthic infauna and how these small creatures could be the key to understanding successful restoration in the Indian River Lagoon. Infauna, what is it and why is it important on this episode of One Lagoon, One Voice.

Duane De Freese:

Hi, I am Duane De Freese, executive director of the IRL Council and the Indian River Lagoon National Estuary Program. Welcome to our One Lagoon, One Voice Podcast.

Each week, myself or one of my staff members will host leaders in the community, scientists along the lagoon, people who know a lot about the system to talk about some of the problems.

And most importantly, some of the solutions to solve the Indian River Lagoon’s health and make sure it’s great for future generations. So let’s get the show started and let’s talk a little lagoon.

Daniel Kolodny:

Welcome everyone to today’s episode. I’m Daniel Kolodny, the Chief Operating Officer of the Indian River Lagoon National Estuary Program.

To help discuss infauna and all the amazing things that we are learning about them, we have Dr. Holly Sweat from the Smithsonian Marine Station in Fort Pierce with us today. Holly is a marine biologist who specializes in biodiversity and benthic ecosystems.

Holly, welcome to the show.

Dr. Holly Sweat:

Thanks, Daniel. I’m happy to be here.

Daniel Kolodny:

We’re so glad to have you.

Holly, can you tell us a little bit about yourself and what you do at the Smithsonian, all the work you do there?

Dr. Holly Sweat:

Sure. So, I lead the Benthic Ecology Lab here at the Smithsonian Marine Station in Fort Pierce, Florida. And benthic is just another word for bottom dwelling. So we focus on all of the organisms that live on the seafloor, on the estuary floor and how they interact with their environment.

So, I lead a group of people through various different, projects that focus on benthic ecology, which I’ll get more into later on today. And I’ve been working in the lagoon system for about 23 years now, basically my entire career, and a lot of that has been with the Smithsonian. So I’ve really come to be connected with the lagoon and really invested in making sure that it’s sustainable and that it’s healthy.

Daniel Kolodny:

Excellent, thank you.

So before we dive into this discussion today I just kind of want to shamelessly plug one of our other episodes and let our listeners know if they haven’t already listened to episode 18 “Get the Muck Outta Here” that this discussion today that I’m having with you is actually kind of a, not only will be an amazing standalone podcast, but it was a follow-up to that discussion I had with Austin.

It was really interesting. We were talking about sediment and how to fix it, and make it healthy. And we talked about infaunal communities and it came up in that discussion and it gave me an idea for our next podcast. I said, “Oh, we gotta get Dr. Holly Sweat here to talk about that.” So, well here we are and we’re talking infauna today.

So now that we get into infauna and benthic infauna, can you kind of tell me a little bit about what kinds are there?

Dr. Holly Sweat:

There’s so much.

Daniel Kolodny:

(laughs).

Dr. Holly Sweat:

I guess I should probably back up a little bit. This goes back into my career history a little bit, but I am a child of the eighties and early nineties. And so I grew up watching things like Honey, I Shrunk the Kids and I was just immediately blown away by the idea that our perception of the world around us is shaped by our size.

And there are things that are going on that make the world go round that we never see.

It’s happening 24 hours a day, seven days a week. We would not exist without these things happening. And yet we really don’t know a whole lot about them. And so everything that I study with infauna and all of the other tiny organisms that we look at, it all kind of goes into that whole idea of these little animals helping to shape the world around us, making it possible for us to have a clean environment putting food on our table, all sorts of things.

So, there are lots of different types of infauna that play different roles that help to engineer the world around us.

So we’ve got organisms like worms, kind of think about the earthworms in your garden, for example. We have the same sorts of worms in the marine environment that will burrow around in the sediment.

We have shrimp and shrimp relatives that are gonna be at the top of the sediment and climbing on the seagrass and, you know, going up and down in grass beds and other habitats. We’ve got snails and then a whole lot of other organisms that you probably have never heard of before because they’re, you know, very small groups.

But there is so much diversity there and they all play important roles. Like, you know, just for example, I have somebody in my lab that’s, that their entire career is focused on studying micro turbellarian flatworms. So these are tiny, tiny little worms that live between grains of sand. That’s how small they are.

Daniel Kolodny:

Wow.

Dr. Holly Sweat:

But they’re one of the most abundant organisms in sand and mud. When you go out and you walk in the lagoon, they’re super abundant under your feet.

And they have all sorts of different services that they provide from cycling nutrients to just making the sediments healthier.

So yeah, I could go on and on. There’s so many different types of infauna. I’m sure we’ll get into details about some of those today.

Daniel Kolodny:

For sure. So you told us a little bit about, you know, where they live. Are there preferred conditions that they like? Um, are there any outliers, you know, like most of them live in on top? Are there some that prefer different areas?

Dr. Holly Sweat:

There are, yes. So I’m probably gonna be bringing this back to discussions of land-based ecosystems a lot because-

Daniel Kolodny:

Right.

Dr. Holly Sweat:

…it’s easier for us to connect with. So I’ll be talking about like what happens in your backyard, what happens in your garden. Those processes are very much the same in marine environments. We just don’t see them ’cause they’re under the surface of the water.

So like you have in your yard, there’s a lot of infauna, a lot of organisms that are happy pretty much anywhere. They’re what we call generalists so they can survive in really clean sand, you know, sediments that are what we would consider pristine, nice beach sand. They also can live in mucky, muddy, kind of gross environments as well.

Daniel Kolodny:

Mm-hmm.

Dr. Holly Sweat:

Then we have some that are more like our weeds. They can live everywhere, but they tend to do really well in those bad environments because they’re the only things that can survive. And so they don’t have any competition from other stuff.

Daniel Kolodny:

Gotcha.

Dr. Holly Sweat:

And then we have some other things that are really sensitive and so they’re gonna be indicators of nice healthy environments. You know, things like, orchids and other, you know, sort of rare plants in your yard. We have infauna that are like that, that are only gonna pop up when, when the environment is healthy.

Daniel Kolodny:

Gotcha.

I assume most of these infauna need aerobic conditions. Are there any that can survive in anaerobic? And that means, you know, with oxygen or without oxygen.

Dr. Holly Sweat:

Yeah, so most of them are gonna need large amounts of oxygen, but there are a bunch that can survive with very little and even sometimes no oxygen for short periods of time.

So we have certain species that have the ability to sort of, no pun intended, kind of clam up whenever there’s no oxygen around or when there’s, you know, inhospitable conditions and they can kind of wait it out.

And we also have some animals that have the ability to withstand sort of chemical byproducts of having a really low oxygen environment. So when we don’t have oxygen, we can have microbial or bacterial processes that produce things like toxic hydrogen sulfide, that rotten egg smell that you get whenever you go out in the lagoon and you smell sediments that don’t have oxygen that can kill most things.

But we have some infauna that are specialized to be able to live in that. There’s a clam, for example, that we study in my lab called, the scientific name is Millennia Lateralis. It’s called the dwarf surf clam, I think. And it has the ability to withstand hydrogen sulfide concentrations that are many, many times higher than we can withstand. They can live for days and concentrations that would kill us in a few minutes, so…

Daniel Kolodny:

Wow, that’s impressive.

Dr. Holly Sweat:

Yeah.

Daniel Kolodny:

And I know we’re gonna touch about this later, you know, when we talk about healthy sediments and muck and that kind of stuff. So just really interesting to hear about all the different types of conditions these little fellows can live in. So, really interesting stuff.

I think what really has got me so excited about this topic is that, you know, when we think about biodiversity and species discovery, there’s still, this is a frontier that hasn’t been fully explored. I was so fascinated at the last symposium to hear about, you know, new species still being discovered. Can you…, how is this possible that we don’t know about all these species?

Dr. Holly Sweat:

Yeah. So we are fortunate in the Indian River Lagoon to be in a place that’s really well studied and we’ve had things like the Indian River Lagoon Species Inventory that’s existed for decades now and a lot of other work in the lagoon that has allowed us to create an inventory and to take stock of how much diversity we have. But we are still finding so many more species because we are starting to look in habitats that have been understudied for all of scientific history.

Daniel Kolodny:

Right.

Dr. Holly Sweat:

So it’s hard to study these small things. You need specialized equipment, you need certain microscopes, you need certain ways of collecting, and then you need a lot of taxonomic or identification expertise.

So people train for years to be able to study some of these different groups, and there’s only a handful of folks worldwide that can identify certain types of species. So luckily we’ve had a lot of folks that have those areas of expertise come and work in the lagoon recently. And so they’re shedding light on this sort of black box of organisms that we didn’t know we had.

Daniel Kolodny:

That’s amazing.

So what does this… all this new info mean? You know, all these new species, what does it tell us about the lagoon and what’s going on in, in these sediments?

Dr. Holly Sweat:

I think we’re at very early days of figuring out the potential of all the things that these species can tell us about our environment because some of these are new to science.

So within the last few months, for example, we’ve had folks here at the Smithsonian Marine Station that have identified probably at least 50 different species that we think are new to science.

Daniel Kolodny:

Wow. (laughs).

Dr. Holly Sweat:

So we don’t know a whole lot about them yet ’cause we’re just now getting descriptions and putting names on them. So the ecology will come whenever we have time to further explore the role of these animals in their environment.

But I think we can learn a few different things from this. We know generally what these different groups of organisms do in their environment and we know it’s always good to have higher diversity because that can buffer an ecosystem from change.

So things like climate change and pollution and urbanization and stuff like that, if you’ve got a more diverse ecosystem, then there are gonna be organisms that can take the place of others that might die off from a particular disturbance event. So it’s always good to have more species.

So just discovery of learning how much diversity we have in the lagoon, but also, eventually understanding how these different species can provide different services to help keep our ecosystem healthy.

Daniel Kolodny:

Right.

Dr. Holly Sweat:

So it seems like we should know everything, but turns out we don’t.

Daniel Kolodny:

Yeah. But what you do know is really important to this point. And so that’s a good way to kind of transition into why we know infauna is so important.

So let’s talk about the health of our sediments and talking about restoration. You know, the lagoon’s gone through so much degradation over the past decade and so much seagrass loss. And so when we’re talking about sediments and keys to future restoration, you know, when I was talking with Austin, we were really talking about, you know, how do we get these sediments so that they’re healthy, don’t have that hydrogen sulfide, which is a big factor that plays into seagrass loss and recovery.

How do these infaunas impact that sediment health?

Dr. Holly Sweat:

So many different ways.

Daniel Kolodny:

(laughs).

Dr. Holly Sweat:

I’m gonna go back to the whole earthworm analogy. If you are a gardener you know that you need certain organisms in your sediment like earthworms, like beneficial insect larvae and things like that to help make the sediment healthy.

Same thing is happening in the lagoon. Let’s say for example, we’ve got an area where there’s been a whole lot of fertilizers dumped into the lagoon and lots of algae blooms, lots of grass clippings from your yard and all of that stuff has settled on the lagoon floor and kind of blanketed it with this muck layer.

Daniel Kolodny:

Mm-hmm.

Dr. Holly Sweat:

Not very much can live there. There’s only gonna be a handful of animals that can withstand those conditions. And obviously we’re not gonna have things like seagrass growing in those sediments. And so infauna have the ability, some of those more robust organisms that can withstand those conditions have the ability to come in and they’re what we call sort of pioneering species. They can handle the low oxygen, the hydrogen sulfide, anything we wanna dish at them. They’re kind of like the cockroaches of the ocean.

And they’ll come in and they’ll get to work and they have the ability, as long as we’re not, you know, throwing more nutrients at them and throwing more hurdles at them, they can help to restore those sediments ’cause they will burrow through them and the burrowing activity can do what’s called bioturbation. So that helps basically just to mix up the sediment. It helps oxygenate the sediment. It helps to move nutrients around so that the microbes can get at those nutrients and decomposition can happen more effectively.

Some of them have the ability to improve water quality because they can filter the water and bring all of those particles that are in the water column down onto the sea floor.

And all of that is gonna make sediments healthier and condition them for things that are more sensitive and rarer so that eventually you get this kind of what we call succession happening where over time you’ve got a greater diversity of infauna. And when you have lots of different types of infauna, then you’re gonna have healthy sediments. And then you can start to have things like seagrass recruitment and other big organisms moving in and fish and other large predators that eat these infauna moving in and taking advantage of the habitat.

Daniel Kolodny:

So these guys are truly like almost the base of the food web, you know?

Dr. Holly Sweat:

Yes.

Daniel Kolodny:

The start of that whole system. So that’s pretty interesting.

Dr. Holly Sweat:

Yeah.

Daniel Kolodny:

I think another thing people need to realize is that, you know, a lot of these guys, they don’t move very quickly. Right?

Dr. Holly Sweat:

Mm-hmm.

Daniel Kolodny:

Like they’re kind of staying the same place. There’s a few that can move around, but so that’s going to make this take a long time right to recover?

Dr. Holly Sweat:

Yeah. It can take a long time. I always like to say that they’re literally stuck in the mud, like they can’t go anywhere. And that’s why we use them as indicators of environmental health because they mirror the world around them better than something that’s really mobile, like a fish, or a large crustacean.

They don’t move around very much, but a lot of them reproduce pretty rapidly. So if we do restore conditions enough that it supports their reproduction, then there is the potential to have at least these early pioneers kind of colonize pretty quickly.

Daniel Kolodny:

Gotcha. That’s great.

So you kind of touched on it briefly, you know, they can change the chemistry of the sediments to make it more suitable. Can you dive a little bit deeper into that and how that, because that was something that was so fascinating that they can change chemistry of sediments and make it more conducive and just go a little bit more into that?

Dr. Holly Sweat:

Sure, one of those ways is just by oxygenating the sediments when they’re digging around especially the deep burrowers that have the ability to go from the surface of the sediment several inches down where we don’t get any oxygen in the sediments.

Daniel Kolodny:

Right.

Dr. Holly Sweat:

They can just change the chemistry profile and reduce that toxic hydrogen sulfide just by injecting oxygen into the sediment. But they also have this unique ability to kind of almost farm, or culture, different microbial or bacterial communities in the sediment.

There are certain infauna that have associations with different types of bacteria and their behavior just kind of supports building a more healthy and diverse bacterial community, which also helps with cycling excess nutrients and that improves the chemistry of the sediments.

So you can kind of think of it like after you take an antibiotic and you’ve completely flushed your digestive system of all of the good bacteria, then you have to go in and take a probiotic so you can build all of that back up.

Daniel Kolodny:

Gotcha.

Dr. Holly Sweat:

So the infauna are kind of like a probiotic. They’re sort of helping to reestablish that healthy bacterial community that helps with sediment chemistry profiles.

Daniel Kolodny:

That’s fascinating.

So now that we know some of the positive impacts that infauna creates to our sediments, let’s talk a little bit about the negatives and what are some of the things that can harm them.

And so, you know, we kind of already talked about muck a little bit but let’s, let’s dive a little bit deeper into some of those topics. So, you know, hypoxia, nutrient fluxes, hydrogen sulfide.

Dr. Holly Sweat:

Yeah. Most of those things that you just mentioned, they all go back to sedimentation. And so that’s gonna happen whenever we have a lot of inland runoff.

So we get a big storm event, we get weeks of rain and sediment from the soil, from our yard, goes in the storm drains, it ends up in the lagoon. We have fertilizers that are going into the lagoon and causing algae blooms. And once that algae dies, that settles down onto the, the bottom of the lagoon.

Most of our watershed eventually flows into the lagoon. So think of all of the stuff that’s churned up in the water column, that eventually has to settle out, and so we call that sedimentation. It’s just basically the raining down of all of this material onto the bottom of the lagoon. And that can smother these animals, especially if it happens really fast.

Because think about being an animal that’s only about a quarter of an inch long. If you have, over the course of a couple of weeks, an inch, or two inches, or three inches of mud that accumulates on top of you you got to keep burrowing upward climbing upward to the top of that each day just to get some oxygen and keep from getting smothered.

So some of these animals, because they’re so small they can’t outpace the sedimentation that’s happening. And more sedimentation means lower oxygen and more hydrogen sulfide. And that all happens because of the microbial community, the bacterial community, and the decomposition that’s happening with all of the stuff that’s raining out of the water column.

Daniel Kolodny:

Gotcha. And it’s just like a negative feedback loop where it just makes it worse, and worse, and worse. Yeah.

Dr. Holly Sweat:

Yes. Yeah. So that’s one of the big harms to infauna, is that sediment quality, that sedimentation. The other big harm arguably in some parts of our lagoon the dominant driver of infauna health is gonna be salinity swings.

Daniel Kolodny:

And that can also come from rain events. You get these big, large pulses can have these huge swings in salinity. So Yeah.

Dr. Holly Sweat:

Yes.

Daniel Kolodny:

So they’re both tied almost to the same thing.

Dr. Holly Sweat:

Yeah. And especially in our southern lagoon in places like the St. Lucie Estuary where we have releases sometimes from Lake Okeechobee and from of our tributaries, we’re going to get these really big thousands and thousands of liters of fresh water that are coming off the land and that’s gonna drive the entire water column.

Even if we have meters of depth, it can drive it from marine to fresh over the course of, you know, a few days, few hours, and that can wipe them out if they’re not used to dealing with those swings.

Daniel Kolodny:

How resilient are some of these infauna to those swings?

Dr. Holly Sweat:

It kind of depends on what the species are. So we have a group of species that are pretty resilient. A lot of them are the ones that are also resilient to things like hydrogen sulfide and low oxygen.

Daniel Kolodny:

Right.

Dr. Holly Sweat:

But we also have others that are, a lot of them, especially in the healthier sites, in the more diverse sites, that are pretty truly marine. So they live near the inlets or they live in areas where we don’t get a lot of freshwater influence and they can’t handle it. They’re going to be wiped out pretty quickly.

Daniel Kolodny:

So now that we know a little bit about, you know, what they can do for our sediments and helping to improve and all the things that they can’t handle…

What are some actions that our listeners could take to help these infauna? Obviously taking care of their own yards is a big one and their own inputs to lagoon, but is there other things that they could do to help our little bottom dwelling creatures?

Dr. Holly Sweat:

Obviously doing anything you can do within your own routine, within your own life, to reduce your input to the lagoon. I know sometimes it seems to get a little bit daunting or overwhelming, like, “Oh, how are we gonna fix this problem? No matter what I do, nothing’s going to help.” But every little bit goes a long way.

So if you can reduce your inputs to storm drains and reduce your fertilizer use and things like that, that’s going to help. But also by supporting things like muck dredging projects areas where we’ve had lots of muck accumulation, that can help.

Supporting research and supporting monitoring. My lab does a lot of environmental monitoring, that’s what we use all of these infauna communities for. And sometimes monitoring gets a bad rap, but it’s absolutely necessary for us to understand the health of our lagoon, where we are now, where we have been in the past and where we’re going.

We can’t figure out a trajectory and forecast what the lagoon is going to be like in the future if we don’t have good long-term data. So supporting that and getting involved with monitoring efforts, there’s a lot of citizen science efforts throughout the lagoon, so get out there, get involved with institutions, organizations that are doing work on the lagoon.

And beyond that, just get out there and use the lagoon. Become familiar with it, have an appreciation for it, and that is going to help spread the word throughout your community of what a unique resource this is, and I think that that’s how we get started in conserving everything, is to get everybody on board.

Because we’re all in this together, it’s not just a scientist problem, it’s not just a particular neighborhood issue. Everybody that lives here has to get involved.

Daniel Kolodny:

For sure. And you know, that sense of stewardship is obviously key to everything, but I do want to… you touched on two things that are really important that I think can go a long way in helping promote that sense of stewardship.

And that’s, you know, that monitoring and seeing first-hand the outcomes of some of that like muck dredging for example. You know, they have sampled the infaunal community before and like you said, there’s very few that can live in that. And then after the muck dredging, I know I talked with Austin about this, in Turkey Creek, they dredged all the muck and then immediately we started to see more infaunal communities start to come back up. So, you know, that’s one of those ways to just, “Okay, this works. You know, I monitored it before, monitored it after, it’s working.”

Dr. Holly Sweat:

And I think that also helps people appreciate trying to reduce the inputs into the lagoon. Because we can have a muck dredging project every year.

Daniel Kolodny:

Forever.

Dr. Holly Sweat:

Forever.

Daniel Kolodny:

(Laughs). Yeah.

Dr. Holly Sweat:

And we’re never going to get rid of it if we keep pumping it into the lagoon.

Daniel Kolodny:

Right. Got to stop it at the source.

Dr. Holly Sweat:

If you can see the benefits of the dredging and what stopping that sedimentation is going to do I think it goes a long way toward turning off the tap of all the inputs too.

Daniel Kolodny:

Well, thank you so much for this opportunity to talk infauna. I’ve been super excited. Is there anything else you’d like to add to our discussion before we wrap it up?

Dr. Holly Sweat:

Well, I guess I’d probably like to plug the Indian River Lagoon Species Inventory. If you haven’t been on there before, it’s irlspecies.org.

Daniel Kolodny:

For sure.

Dr. Holly Sweat:

It is the most comprehensive database of information on species and habitats for the Indian River Lagoon System. So if you’re out there and you’re beach combing or, you know, just kicking around in the lagoon and you want to identify something that you found you can hop on there and that can help you out.

Aside from that just thank you so much for giving me a platform to nerd out for a little bit and talk about these animals.

Daniel Kolodny:

Yeah, I love talking about these. Does the Smithsonian have any socials that anybody can follow? Just curious.

Dr. Holly Sweat:

We do, yeah. Thanks for the reminder.

My lab is on Instagram. We’re at @smithsonianbenthicecology.

We just had a benthic bio blitz, which is basically a scientific scavenger hunt for a lot of these organisms that go sort of understudied. Over the last two weeks, we invited about 30 experts from lots of different locations here to help us go out, collect, identify, catalog, photograph, and take tissue samples from about 1800 different specimens from 32 sites in the lagoon.

Daniel Kolodny:

Wow.

Dr. Holly Sweat:

So we went from sort of the Sebastian Vero area all the way down to Jupiter Inlet. We did a little bit of near shore sampling as well.

And our goal was to obviously catalog species and sort of increase that tally of organisms we know about from the watershed, but also to get DNA sequences of all of these animals because we can use those to flesh out these public DNA sequence databases that are used for something called environmental DNA, which is probably like a whole other podcast episode.

Daniel Kolodny:

Awesome. Any new species during the bio blitz?

Dr. Holly Sweat:

Oh, so many, so many new species.

Daniel Kolodny:

So cool.

Dr. Holly Sweat:

We probably have over a hundred records that are new for the lagoon.

Daniel Kolodny:

Wow.

Dr. Holly Sweat:

And we probably have dozens that are new to science.

Daniel Kolodny:

Excellent.

I’ll just add, you know, I love that species inventory webpage. I use it all the time, and I love that you guys are adding constantly new species, new features, new tools for the public to be able to help identify and see what kind of species are out there. So it’s really quite an amazing website.

Dr. Holly Sweat:

Thank you. Well we couldn’t do it without the help of the IRLNEP too, so, thanks a lot. And we’re gonna continue to grow it and hopefully it’ll become a resource that is better and better and better every year.

Daniel Kolodny:

Excellent. Thank you very much, Holly.

Dr. Holly Sweat:

Thanks, Daniel.

Daniel Kolodny:

Thank you for joining us today. If you enjoy these discussions about the Indian River Lagoon, please like and subscribe to this podcast.

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