With each issue, Trib+Water brings you an interview with experts on water-related issues. Here is this week's subject:
Lucas Gregory is a project specialist and the quality assurance officer at the Texas Water Resources Institute at Texas A&M University. He is also program coordinator for the Center for Invasive Species Eradication. He previously worked on a project looking at giant salvinia in Caddo Lake.
Editor's note: This interview has been edited for length and clarity.
Trib+Water: Could you tell me a little bit about your work related to invasive species in state waters?
Lucas Gregory: We've had several different projects over the years here at the Texas Water Resources Institute that have focused on dealing with invasive species.
One of those was giant salvinia up at Caddo Lake ... and that project was basically put together to look at methods to address the giant salvinia on Caddo Lake and then other lakes as well.
We primarily looked at how biological controls could be used, and used more effectively to combat the spread of giant salvinia. There is a salvinia weevil that is a host-specific insect that feeds on salvinia and lays its eggs within the plant. And then whenever the eggs hatch, the larvae eat their way out of the plant and effectively kill that plant.
That project focused a lot of research into better understanding the weevils’ biology and what may or may not make it effective up at Caddo Lake. And then we also did some chemical trials and things like that up there to see if there were other combinations of chemicals or application rates of chemicals that were more or less effective than others.
The other invasive species project that we've dealt with here at the Institute has been battling salt cedar. That's a riparian plant that likes to colonize riverbanks and is more common in the western part of the state.
We worked through the Pecos River Ecosystem Project to use both chemicals and biological controls to minimize the spread of salt cedar on the Pecos River. The biological control is a primary mechanism that we utilized, and, over the course of that project, we were able to actually establish self-sustaining colonies of the salt cedar leaf beetle out there that have since basically gone on to do their own thing and are continually feeding on salt cedar year after year after year, eventually leading to the plants’ demise and allowing native plants to come back in as the salt cedars’ stand is lessened.
Trib+Water: I know there’s been salvinia discovered in the state at Lake Fork reservoir recently. Why is the presence of salvinia in our state a cause for concern?
Gregory: The biggest concern with giant salvinia is that it is a very aggressive plant and it rapidly expands under ideal conditions. The plant can double in size in four to seven days.
So, in theory, if you have a one-acre area of giant salvinia today, one week from today it could be two acres in size. Once that keeps on perpetuating, it grows exponentially and you can go from not very much salvinia into a whole lot of salvinia in a very short amount of time.
In fact, we've seen that at Caddo Lake in years past where you would start the growing season with maybe 100 acres of giant salvinia, and you would end the growing season with several thousand acres of giant salvinia.
The presence of salvinia is pretty troubling just because it has the potential to really just go wild and take over a lake. And once it forms or grows like that, it starts to form very dense mats on the surface of the water and basically it chokes out other vegetation. It minimizes the amount of dissolved oxygen that can diffuse into the water, so that in turn chokes out aquatic life reliant on that water.
The waterfowl don't really land on it or won't use it or anything like that. It really kind of eventually leads to the ... uninhabitableness of the ecosystem there. So it really does need to be dealt with in a rapid fashion …. Because once it's there and once it's established, it's really pretty difficult to get rid of completely. It can be managed, but it takes a ton of work.
Trib+Water: How are invasive species in water generally spread to the state? What can people do to help limit the spread of invasive species?
Gregory: The best way to prevent invasive species issues is to not have them to start with at all. Prevention is by far the best and cheapest way to deal with these guys.
The way they get here is usually through human action. In the early days, a lot of these plants were kind of traded around in the aquatic garden industry or even, I've heard anecdotal stories of salesmen that used to go door to door. They would bring a pretty plant to the lady of the house, whenever they make a sales call and oftentimes they were an invasive species.
So I've heard of those stories. I don't have concrete evidence of that, but I've at least heard that story ... But, anyway, people are the main cause of those plants moving from Point A to Point B.
With the giant salvinia, I guess the more common way it's spread from water body to water body is by moving on boat trailers ... I've heard stories of wildlife moving it from lake to lake, so that's a possibility as well. But like I said, keeping them out is the best approach from the start.
Like with the boats, just being mindful of it and actually checking your trailer. Making sure that there's not any vegetation hanging onto your trailer or anything like that is a good measure ... I don't know that there's any one thing that could be done that would prevent the spread of it with 100 percent certainty, but really just raising the awareness is the big thing.
Trib+Water: What are the main controlling methods for invasive species?
Gregory: There are three primary methods for addressing invasive species issues. Biological is one category, and that can be a number of different biological agents, whether it's a weevil or a fly or whatever other critter that's out there.
Usually they're insects. Sometimes it's like a mold or something like that, but most of them are insects and they are host specific organisms.
A second type is chemical. Of course, that's something manmade that you can apply to a plant, and it will do its job. And they're common chemicals in a lot of cases. They are commonly used in agriculture, but it's more of the type of plant that they can kill.
They're very effective in a lot of cases. They are expensive. A lot of times, the chemicals that are sprayed are not selective, and they'll kill a variety of plants, not just the invasive species.
But in many cases, that's a very reasonable price to get rid of that invasive species or at least knock it way back to give those other plants a chance.
The last large type of management measure is mechanical removal of the plant. That can be as simple as going out and removing it by hand, dipping it out with nets or using big mechanical devices to remove the plant ... That method is also pretty effective in a lot of cases. It's usually relatively slow and also pretty expensive.
They all three have their pros and cons. But with an infestation like giant salvinia, you're probably really never going to get rid of it once it truly does take hold in the lake. It becomes a long-term maintenance and management issue. If you look at their cost versus the benefits and things like that, you usually have to take a toolbox approach and utilize two or three of those large methods.
Trib+Water: Is there anything else you'd like to note?
Gregory: Just that it's definitely something that needs to be addressed and dealt with. Because if we just sit back and do nothing, a lot of our unique natural resources are going to get overwhelmed with these invasive species.
It may seem like kind of a hopeless fight, but keeping on fighting is definitely a necessity. Because if we don't, we'll lose all of our things that are worth fighting for out there in the environment.