Episode 19: All About Mosquito Impoundments

Unintended consequences. Sometimes when you try to fix one problem, it can have unexpected impacts on something else.

For instance, during the 1950s and early 1960s in Florida, various mosquito-control efforts impounded approximately 39,500 acres of coastal marshes in the Indian River Lagoon by constructing low, earthen dikes around the high marshes, which did help to control the population of buzzing biters.

While the salt-marsh mosquito was better controlled, cutting off these areas from the lagoon had other unintended effects.

The good news is mosquito impoundments are now being better managed, and even more exciting, they’re being reconnected to the Indian River Lagoon. And best of all, some of these impoundments are being used for innovative restoration projects too.

Today, we’re going to talk the buzz surrounding some of these projects on this episode of One Lagoon – One Voice.

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.

Welcome to the One Lagoon – One Voice podcast. I’m Heather Stapleton, one of three community engagement coordinators for the Indian River Lagoon National Estuary Program. Today we’re going to chat about mosquito-control impoundments that have affected approximately 39,500 acres of coastal marshes in the Indian River Lagoon.

The main goal of those impoundments has been to control the salt-marsh mosquito — and they have done just that. But we have learned that cutting off these areas from the lagoon itself negatively affects fish populations and the overall ecosystem function. So today, some of these connections are being restored. And beyond simply reconnecting these areas to the lagoon, they’re even being used for very innovative lagoon restoration projects and research.

Today I have three guests joining me, Dave Fuss the Director of Land Stewardship with the Indian River Land Trust in Indian River County.

Hi, Dave.

Hi, Heather.

Thanks so much for being here.

Oh, I’m looking forward to it.

Great. We also have Dr. Jon Shenker — professor emeritus of Florida Institute of Technology. Hey, Jon.

Hey. Good afternoon, Heather, and good afternoon, everybody. Thanks for inviting me and giving me a chance to talk about fish in the Indian River Lagoon.

We know you love all things fish, for sure.

Absolutely.

And then finally, our third guest, Dr. J. Cho, professor in the department of integrated environmental science at Bethune-Cookman. Thank you for being here, J.

Thank you for the invitation.

Yeah, we really look forward to hearing about all of the projects. All of you have been partnering with the Indian River Lagoon National Estuary Program for quite some time. So first of all, thank you for those long-standing partnerships, beyond just simply being here today.

I know that all of you have been very interested in lagoon restoration projects. And through some specific projects that you’re working on now, and will be continuing to work on in the future, I believe that you also have unique perspectives on mosquito impoundments.

In fact, all of you have figured out unique ways to make even better use of these already altered ecosystems. Dave, could you tell us a little bit about the history of mosquito impoundments? What are they and why do they even exist?

Sure, Heather. Mosquito impoundments are former salt marshes that line the lagoon edge. Mosquito control has been interested in trying to control those salt-marsh mosquitoes… trying to make it a little bit more hospitable to human inhabitation.

So, earlier on, there was an effort by the mosquito-control districts to ditch those salt marshes and try to eliminate or reduce the mosquito populations. But ultimately, that was not successful. It was not deemed effective.

So beginning in the 1950s, the mosquito-control districts started experimenting with creating an impoundment around these salt marshes. And that was done by essentially creating a hand dug or machine dug dike around the salt marsh and then filling the interior with lagoon water. And that sort of seems counterintuitive for people that are familiar with fresh-water mosquitoes that lay their eggs in the water.

But salt-marsh mosquitoes need to lay their eggs on exposed mud — they’ve adapted to the tidal cycles. So, by flooding those areas during the breeding season, it disrupts the reproductive cycle for the salt-marsh mosquito.

Can you imagine having been involved in that early work, especially that which was done by hand?

I’m sure that was part of the reason they wanted to try to do that from the malaria and other diseases that mosquitoes carry. That’s really one of the reasons that mosquito-control districts exist.

But one of the things that have helped considerably with that is, prior to that, there was a lot of use of chemicals to control the mosquitoes. If you recall, in the 1950s and ’60s, it was DDT that was primarily being used, which had cascading catastrophes in the environment and to a lot of wildlife.

So this method is a way to get away from the use of pesticides.

Of course — but then having other unintended consequences. Every time you try something new, there is the potential for unintended, negative consequences always, for sure.

So Dave, why do we have so many impounded salt marshes in the Lagoon region? It’s over 39,500 acres. That seems pretty significant.

Well, all those areas that were salt marshes before were, of course, very productive habitats for a variety of wildlife. But they were also reproducing a lot of mosquitoes.

So the mosquito-control districts, after that early experimentation, sort of adopted this strategy of using the mosquito impoundments to control the salt-marsh mosquitoes.

Each of those counties and their mosquito-control districts started using this technique, and that’s why a lot of the salt marshes are no longer really functioning quite like the original salt marshes. Salt marshes are quite rare in the Indian River Lagoon at this point in time.

Right. You know, mosquito control is very important, both for the comfort and even the health of Floridians.

But by cutting off so many acres of marsh from the lagoon, we have affected the ecosystem function. We have affected the animals that live there.

Jon, though we did control mosquitoes by impounding, what were some of those unintended negative consequences from that?

A lot of the early efforts in that really didn’t understand the function of the mosquito-control impoundments for things other than mosquitoes. And it turns out that these marshes are very valuable nursery habitat for fishes — at least some species of fishes.

By blocking off access to the impoundments, a lot of fish were not able to get their babies into the impoundments. And if babies somehow got into the impoundments, they could not get out again.

Right.

Removing 40,000 acres of nursery productivity from the Indian River Lagoon potentially had some pretty significant impacts on at least several species of fish.

Right. So now having figured out those negative effects, what have some of the mitigation efforts been?

A variety of things have been tried. A lot of this work goes all the way back to the 1980s when Dr. Grant Gilmore from Harbor Branch and Jorge Rey from the University of Florida really started trying to figure out ways to restore the nursery function of the mosquito impoundments.

Some of them are actually determining which impoundments may not really be functioning for mosquito production and then permanently breaching the dikes, creating a permanent passage in and out, so fish can move in and out on a normal cycle.

In other areas, yes, a lot of mosquitoes are being produced. They need to try to control them. But fortunately, mosquito reproduction is heavily focused in the summertime. So what they decided to do was develop a technique that we call the RIM technique.

Right.

Rotational Impoundment Management. And the idea there is [to] create water connectivity to a series of culverts.

The culverts would connect the Indian River Lagoon to the interior of the impoundment. And these culverts would be opened in the fall and the winter and the spring to allow fish and water to move back and forth.

Right.

But in the summertime, when the mosquitoes are breeding, let’s close off those impoundments. Let’s pump those impoundments full of water and prevent the mosquitoes from breeding.

And then in the fall, open them up again and go back to the normal hydrological and hopefully biological connections.

Right. About how many of the impoundments have what you just mentioned, the rotational impoundment management?

That’s a really good question. I think we’d have to check with each and every mosquito-control district because each one has their own records and their own particular functions.

I think in Indian River County, almost all of them now are under RIM.

Mm-hmm.

In Brevard County, most of the impoundments are under RIM. A significant number of them have been permanently breached. And the breaching technique is kind of interesting. They frequently involve dynamite.

Some of my ex-students who work for various environmental organizations were in charge of taking demolition teams out across the Indian River Lagoon in little boats full of dynamite in the middle of thunderstorms to blow holes in the dikes.

Little boats full of dynamite sounds pretty exciting.

Yeah. I like to think of marine biology as a totally immersive subject. But that might be a little bit too much for my taste.

Maybe a bit much. So today, these impoundments have provided surprising opportunities for restoration efforts.

All three of you really have been able to take advantage of some unique situations for some interesting projects.

J, your project focuses on establishing a population of native seagrass species within the impoundment. Tell us about the location of the impoundment and kind of what your students have been up to in order to try and establish seagrasses there.

Yes. So I want to go back and then give a little bit of background. Unlike these two gentlemen, who talked about mosquito control, I kind of learned more organically about these systems.

I moved to Daytona Beach in 2011 from Mississippi. I did my seagrass work in Mississippi and before that it was Louisiana. So I moved here and then I wanted to continue some seagrass work. But Bethune-Cookman is far away from the India River Lagoon and it was kind of limiting us to go to the locations. And there are so many people who are doing seagrass work here for decades.

So I was trying to find my niche, right?

Yes, yeah.

I was really interested in these impounded areas before I knew how they were used for mosquito control.

So this species, Ruppia maritima, which is called the wooden grass, is not true seagrass. I mean, for me, it’s a seagrass species. But a lot of seagrass biologists don’t want to call it a seagrass because they tolerate marine conditions. They can also occur in near-fresh water.

Mm-hmm.

They can survive in hyper-saline conditions. Some areas of the different species of Ruppias spotted in marsh have neared 100-part-per-thousand somewhere in Europe.

So they tolerate a wide range of salinity. We call it the euryhaline species. Ruppia Ruppia Ruppia

Okay.

And we wanted to see… it’s not about, “Okay, we’re going to use this as a restoration site.” [Although] that is in the back of our minds — that is the ultimate goal. But we wanted to see whether we can use this type of impounded area as a potential source-habitat for Ruppia that can be used for establishing initial beds of seagrass in the Indian River Lagoon Restoration.

So we transplanted Ruppia. Initially we used nursery-growing Ruppia, using three different types of transplanting units. So one is the plug, the small one — each plug has one shoot. We also used the pea-pod unit. The pea-pod has probably three or four shoots. Then we used a cotton bag that had five to seven of the shoots.

We transplant them after these impoundments were closed because we have to wait until the water level reaches a certain level. We talked about the RIM, [which] works perfectly with actual Ruppia because the impoundment is closed early spring. Then we transplant seedlings or small plants.

It usually takes only two months in a good situation to mature and produce flowers and seeds. That’s the time impoundments become too hot, too warm, too turbid, too murky for anything to grow. So we would like to use this short time period for transplanting Ruppia. Then they produce enough seeds, and then they drop the seeds so that we maintain a viable seed bank.

So that is the one of the things that we did, and we monitored monthly — truly bi-weekly and then later monthly. Oh, another thing is we also collected the sediment to look for any viable seeds [in the impoundments].

That’s very interesting.

Yes, so we used those seeds to test [their] viability. [We] also used them to germinate in the laboratory and then we plant them in the impoundment.

You know, beyond just doing projects, communicating about the projects and communicating about the progress is so important.

And J, your proposal also talked about two different education opportunities. One was with the general public and then another one for actual restoration professionals.

Could you tell us a little bit about those effects?

Yes. First of all we involved volunteers from different organizations and also from our university. So that is first-hand education for the students and young adults who were involved. And FWC was also part of it.

They actually funded a portion [that matched how much we spent when] we purchased the Ruppia plants. They also came out and gave a talk at their meeting. I think it’s Coastal Habitat Integrated…

Management.

Monitoring, monitoring.

Oh, monitoring. Okay.

Yeah, so we gave a talk to about 150 Florida wetland managers and other scientists. We also developed the protocol to use Ruppia seeds.

We used the Ruppia seeds to grow the seagrass in the nursery system, and that has been shared with seagrass-nursery owners and then other seagrass biologists and restoration practitioners.

Yeah, that’s really exciting because seagrass is such a hot topic. You know, everyone is learning all the time about how to transplant seagrass and how to grow it in a nursery and how do we determine when the seeds are viable.

I know that the Indian River Land Trust has been conducting a very different kind of restoration project. But again, still in mosquito impoundments. Some of those phases have been completed and some are yet to begin.

David, your project has really focused on increasing the value of mosquito impoundments as vital fish nurseries. That’s something that the marshes used to do naturally on their own prior to having been impounded.

Can you tell us about the location of your project? In a presentation that I’ve previously heard, you talk about how there are two almost very distinctive impounded areas.

Yeah, the land trust has been working with Jon and the mosquito-control district for a number of years now. [The land trust is] primarily at the Bee Gum Point Preserve, which is in the town of Indian River Shores on the eastern side of the lagoon.

We also, more recently, looked at a couple of other impoundments that are in Indian River County on the western shore of the Indian River Lagoon. So as you mentioned, Bee Gum point is a pretty unique impoundment. It’s about 111 acres and it’s divided by utility easements. So it’s effectively two very distinct areas — there’s a lot of open water.

All of these impoundments that we studied share that characteristic of a lot of open water for fish habitat, but surrounded and fringed by a lot of mangroves that the prop roots allow for them (the younger juveniles) to hide from predators. It makes them very good nursery habitats.

So what we’re really trying to do is look at ways that we can try to boost that nursery function, as Jon was talking about earlier. The idea was to experimentally manipulate some of the water levels during that closed period when the water levels are usually flooded and there’s not a connection with the lagoon. So to open those impoundments up, [we] open the culverts and allow water exchange so that fish and other aquatic organisms can pass back and forth.

During that time, the research team was basically catching and then tagging and tracking the movements of a lot of these juvenile fish — primarily focused on tarpon and snook, which are popular game fish. They used passive-integrator-transponder tags, otherwise known at PIT tags.

Right, which people might have in their dogs.

They might have in their dogs.

Exactly.

Right.

It’s the same technology that the Easy Pass uses for their toll system on the interstate.

Right.

So when the fish are equipped with these tags, there are antenna arrays that are mounted on each of the water-exchange culverts and allows the research team to track the movement of those fish in or out of the impoundment.

[This] determines whether opening these culverts during those closed periods can be a way to boost that nursery function.

Right. And Jon, you’re our obligate fish guy. You’re all things fish. What species of fish has been the focus and why those particular species?

Impoundments are really different ecologically than the surrounding Indian River Lagoon. I would love to get your audience down there to see what these impoundments are like because they’re not what they think — what they’re envisioning.

First off, most of the impoundments are very shallow. They have some pretty nasty water in them.

Wait a minute, wait a minute. When you say, “Nasty,” specifically what are you referencing?

Well, they’re isolated from the Indian River Lagoon. Even under good conditions, there’s a lot of backwaters there [so] they see very little water flow through them. The oxygen level can get very low — even down to almost zero.

It’s not at all uncommon to go to an impoundment and you can smell the hydrogen sulfide coming out of the water, and that tells you that the oxygen level is incredibly low. If I can talk you into getting into the water (some people are convinced that this would be a fun thing to do), they discover that this really smelly water has got almost zero visibility.

And underneath it is anywhere from six to maybe 24 inches of loose mud. This is not a pleasant environment to go swimming in or wading in, but on the other hand, some species of fish can handle this. The fish that particularly do well in this for a nursery are tarpon and snook because they have the ability to live in low-oxygen environments.

Tarpon will come up to the surface and they can gulp air from the surface — so they can live in low-oxygen environments that way. Snook have a physiological capacity that is more pronounced when they’re really small, [so they] can live under low-oxygen environments. And they lose that a bit as they grow up.

But the reason they like this type of environment as a nursery is there are very few fish predators in this type of region. There are bird predators there, but there are very few fish predators because not many adult fish can get into these environments and survive. This is why they’re so valuable for tarpon and so valuable for snook. That’s really what we’ve been focusing on.

A lot of our research is how do we get these tarpon and snook into the impoundments when they’re really small — typically we’re talking about larvae that are anywhere from a couple of weeks to a month or two old. And then how do we then let them get out of that impoundment? Because as they grow they have to move onto the next portion of their life cycle in a larger environment.

One thing we found in Bee Gum (and we’ve seen in other locations) is if we don’t get those one-year-old juveniles out in time, they stay in the impoundment. And what do they feed on? Well, they feed on the next crop of juveniles coming in.

Oh, no.

So cannibalism can be a real problem in these types of environments if you do not provide a mechanism for the older juveniles to get out and move on to where they should be moving into.

Definitely something that’s not helpful — but good thing you’ve figured that out.

Well, we’ve come up with some ideas that work at times and unfortunately don’t work all the time. But what we discovered in a project we did about five, six or seven years ago was we could go to the mosquito-control impoundment in the summertime when it’s pumped full of water — it’s closed off and isolated from the lagoon.

We found that the tagged tarpon and snook are really active inside the impoundment. In the wintertime, you don’t see them very often passing around the culverts. They seem to be happy where they are. But in the summertime, they start moving like crazy.

So we conducted what we called a dry-down experiment. We opened the culverts, we allowed water to flood out of the culverts and exchange back and forth with the tides for five, six, seven days. And then we closed the culverts off and pumped them back up again to resume mosquito control.

The first couple times we did this, we saw some really dramatic pulses of juvenile tarpon and juvenile snook flooding out of the impoundments. [They] moved into the Indian River Lagoon so they could move into their next habitats.

And do you do any tracking of them once they have left the impoundments and out through the culverts?

I wish we could. But these animals are really small when we put the tags in them. We can’t put in a sonic tracking tag that we would do if we were dealing with much bigger fish.

So unfortunately, once they get out, they’re history. But it is really interesting watching these guys flood. So we tried this again two years ago and we had surprisingly little immigration during the summer dry-downs out of Bee Gum.

One thing we did find is that the bigger tarpon and the bigger snook that were still trapped in the impoundments never left the previous years — [they] would sit right by the mouth of the culverts.

Eat, yes.

My guess [is that it’s] very much like a feeding station. They just sit there in the water flow and just happily eat whatever comes by.

Yeah, I’ve seen that. Even with things like blue crabs just hanging out there at the culvert [and] waiting to gobble up anything that goes by.

Right. This really argues for coming up with some more innovative approaches to try to get the older tarpon and the older snook out of the environment.

Okay.

In the absence of doing these summer dry-downs, they could go in the winter time, but they don’t seem to do that very often.

We saw very little movement to the open culverts in the winter and the bigger guys just sat there, time and time throughout the entire year feeding.

Mm-hmm.

Dave and I have been talking a lot about using different types of culvert systems. Perhaps creating more water flow [and] spending more time and effort identifying which impoundments are truly capable of producing lots of mosquitoes.

And if they’re not capable of producing lots of mosquitoes, let’s go ahead and breach those impoundments to basically bring them back into permanent hydrological connectivity.

Then who knows, maybe we can even get some fishing tournaments going on, where we can get volunteers to come catch the big tarpon, carry them across the road and toss them in on the other side.

I think volunteers would love to do those kinds of things. You know, catch and release, thank goodness it’s so much more popular these days.

Yeah.

I think people could have fun with that.

Yeah. And actually, that’s how we ended up tagging a lot of our fish in the first place. We’re a bunch of marine biologists. We’re not a really good bunch of anglers, necessarily.

So we did have a lot of volunteers from the surrounding community, coming and helping us catch fish so we could then tag them. Then [with] the younger volunteers, particularly the students, I could often talk into helping drag seine nets to catch fish — and that’s pretty productive. But you had to be willing to wade through really deep water and some really, really deep mud and some really nasty water to do that.

Yeah. I love to go seining. But that’s true. Using those nets is always challenging the muckier the bottom and the deeper the muck on the bottom is, for sure.

It’s a lot of fun, however.

It is.

Although, I guess I have a demented view of fun.

I think we get that since you are the fish guy.I just want to thank everyone so much for participating in the activities of the Indian River Lagoon National Estuary Program and doing projects like this.

It’s obvious we are learning from these projects and helping either to restore the flow where possible. Or, if not possible, improving upon these mosquito impoundments for other things, like fish populations and possibly even seagrass nurseries, is really exciting. Land-based seagrass nurseries are pretty expensive — a lot of inputs into there. Using a mosquito impoundment is a unique and interesting way to have a different kind of seagrass nursery.

So, thank you so much for being here with us today and talking about this. I’d like to invite each of you to kind of just give a closing thought and tell us about how to contact you or your organization.

J, would you like to start?

Uh, yes. So I am located in the department of integrated environmental science at Bethune-Cookman University. We are in Daytona Beach, Florida.

My phone number is (386) 481-2793. Or you can email me at choh@cookman.edu.

Thank you.

And Dave, you know Jon hinted at something that you do offer. And that is getting the public out to your areas.

So could you give us a little information about the Indian River Land Trust and how folks, if they’re interested, might sign up for one of those tours?

Sure. We have a calendar of events at our website, which is at irlt.org. We also advertise on our Facebook page and Instagram under Indian River Land Trust. You can sign up for those — RSVP.

We have a variety of different properties where we have volunteer tour guides [who] take people out for about an hour-and-a-half — usually a mile-and-a-half trip. Some of them are focused on birds or plants and some of them are more general. We do offer that typically during the cooler months. It’s a little bit warm in July and August to be tromping around out there right now.

But we’re really looking forward to continuing this collaboration with the Indian River Mosquito Control District to try to, as Jon mentioned, explore other ways to improve the role of mosquito impoundments as nursery habitats. So, it’s exciting.

It is exciting. I’ve been lucky enough to go on, I think, three property tours. And I’ve learned something at each one.

I just love being able to see areas used for recreation as well as helping out the environment at the same time.

Yeah, all of those areas have mosquito impoundments so you’ll get a little bit of history and explanation of what these are. And you can see [the impoundments] up close and personal for yourself.

Right, if what Jon was describing is a little hard for our listeners to imagine, how great would it be to go out and look at one of those culverts and see all the fish hanging out right there. Or to see some of that interesting water that Jon referenced.

And Jon, how about you? How about if folks would like to get in touch with you?

Okay. The easiest way to reach me is by email and that’s Shenker, S-H-E-N-K-E-R, @fit.edu. Or you can also reach me through Dave and the Indian River Land Trust at any time.

And we’re always looking for suckers — our volunteers who are willing to come out and join us in some of these journeys out into the impoundments. We are planning to do a video-camera survey of fish moving through culverts beginning this fall. And [we’re] actually trying to track the fish visually as they move through the culverts.

We’ve done a little bit of work with that, suggesting that this might be an easier way to instrument a lot more of the impoundment than we can with the PIT-tag approach. So we’ll be looking for some help with that.

Cool.

I’d like to also extend an invitation to J to come and take a look at the impoundment booth. We do have a really vibrant Ruppia population in Bee Gum.

We’ve had Dennis Hanisak and his crew looking at it a bit. I don’t know if anybody’s been able to pick up on some of Dennis’s work after we unfortunately lost him this year.

Yeah.

But I have never seen Ruppia as thick and as dense as we see in the Bee Gum impoundment.

I can.

So it’s a pretty cool place.

I can come anytime. I’m taking sabbatical this semester, so my full-time is dedicated to visiting and touring — and yes, field work.

Okay.

Oh, that is so great and another unexpected consequence.

Yeah.

A positive one.

Right.

We have some good synergy going on here.

Yeah, and then in May is when it’ll all start taking off.

Dave, if that video footage turns out to be pretty good, are there any plans on potentially sharing that on the website?

I think people would be interested to see that.

Yeah, and we’ll probably put some clips out on social media as well.

Yeah.

So yeah, hopefully that will work out if the water clarity and the camera resolution are suitable.

Right, yes. With those caveats, that would be really cool. Well, thank you so much for joining us, everyone. I just love your enthusiasm.

I love all the involvement with the Indian River Lagoon, and I am particularly appreciative of the opportunities for other people to get out and see these projects and possibly volunteer for these projects. I think that’s really exciting.

Thank you so much for being here.

Thank you.

Thank you.

It was a pleasure.