Elodea and the Ecosystem:  How the US Forest Service in Cordova is still working to contain the invasive species.
by Emily Goodykoontz | photos by Justin Hartney, Jessica Smith, Abigail Winn, Tim Vandehey, Cameron Shultz, & Emily Goodykoontz When fish biologist Mike Carey moved to Alaska six years ago to do research with the U.S. Geological Survey, not many scientists were worried about invasive species infiltrating the aquatic and terrestrial landscapes of Alaska. “That has changed dramatically in the last five years or so,” said Carey. An invasive species is a term for non-native plants, animals and other organisms that alter or damage the new ecosystems they enter. Carey has spent much of his career studying invasive species in aquatic systems like lakes and rivers. In Alaska, he’s focusing on the biggest invasive threat to the native water ecosystems – Elodea. “Everybody is worried about Elodea. There’s a lot of people studying it, there’s a lot of money to understand what it’s doing, how to get rid of it.” Elodea is the genus name for six similar aquatic plants, also known as waterweed. Popularly used in aquariums and science classrooms, it is the first known aquatic plant species to successfully broach Alaskan waters – an invader in complex thriving native fisheries and ecosystems. For most of its history, Alaska was protected by the nature of its remoteness and by environmental conditions too harsh for most invasive species to take hold. But as human commercial and recreational activities continue to grow, as the global climate warms and conditions in Alaska change, scientists are scanning the proverbial horizons for invasive species encroaching from latitudes further south. “Elodea is an amazingly hearty plant. It’s growing when it’s freezing out under the ice,” said Carey. “It can survive desiccation for a long time, so it could get hooked on a rudder of a float plane and easily get moved to another area.” In a parallel effort, researchers with the U.S. Forest Service and U.S. Geological survey are working to build the scientific community’s understanding of Elodea’s effects on native food webs. And they’re keeping keen eyes on Elodea’s effect on salmon growth – salmon are Alaska’s biggest fishery and pulled in a $678 million ex-vessel value in 2017. Elodea was first noticed in Eyak Lake in 1982, on the southeast coast of Alaska. Since then, its spread across several parts of the Copper River Delta, which is the largest contiguous wetland complex on North America’s Pacific coast. It’s also been found in lakes near Fairbanks and Anchorage. Crucial salmon, encroaching species It’s mid-August, and Carey is up to his neck in the frigid, green water of McKinley Lake, leaning on his elbows over a large floating yellow ring. Above him, white mist obscures the tops of dense spruce and hemlock, the dark green mountainsides of the Chugach National Forest rising steep above the shoreline. Carey’s gaze is focused on the waters below, searching for the flitting silver movements of the juvenile Coho salmon swimming inside a yellow limnocorral, which looks like a floating swimming pool. It is collection day, and Carey will take the Coho back to his lab in Anchorage at the USGS Alaska Science Center(check) to measure their growth. The limnocorrals function as a contained environment for salmon and other aquatic organisms growing in them. Carey, the lead investigator on the project, needs these controlled environments to conduct the experiment. Mesh sleeves fall to the bottom of the lake from the floating yellow ring, keeping some vegetation and critters in, and others out. They are set up in three pairs around the lake – a total of six – one each dominated 80 percent or more by Elodea as aquatic vegetation, and the other containing mostly native aquatic plants. Carey hopes to better understand the effects of Elodea on the native aquatic ecosystem. “While it would be great to get rid of this species, it’s here, so I think we need to understand what it’s doing to the community, understand how it functions in the food web, to get a better understanding of what that impact is going to be,” said Carey. For two years plus a trial first year, Carey and a team of fish biologists and graduate students have returned to McKinley Lake each summer to run the experiment. This is the final leg – and he hopes it will provide enough statistical power to give them a clear understanding of Elodea’s place in the food web. “That’s the goal of the limnocorrals,” said Carey. “To create this controlled environment where we know what’s happening there, so we can do a comparison between these littoral food webs, with and without Elodea in there, to understand that bottom-up effect.” A littoral food web is the chain of who-eats-who or what-eats-what in an aquatic system. It’s the basic circuitry of energy in the system, the interconnections between organisms that dictate how any ecosystem functions, interacts, grows and changes. “We are trying to understand how the different components of the food web are changing, ultimately trying to understand how it influences fish growth and fish condition,” he said. Carey is focusing on Elodea impacts to the growth of young Coho salmon in comparison to Coho rearing among native plants. At the beginning of the summer, he stocked the limnocorrals with juvenile fish that he had soaked in a blue dye, a stable isotope that gets absorbed by structures made of calcium in their bodies. He removes a small, oval bone from the ear of the salmon and measures them like the rings of a tree – the dye leaves a tiny blue ring in the bone growth. “When I look at the otolith under the microscope, I can see exactly when we put that fish in,” Carey said. “And then the otolith is going to continue to grow throughout the summer, so I can measure the rest of that growth from that moment in time.” But he’s not just measuring rings on fish bones. He’s paying attention to their food sources, too. He counts macroinvertebrates, larvae and bugs without spines which the Coho salmon eat, and measures periphyton, the food for the macroinvertebrates – a complex mixture of freshwater organisms such as algae, cyanobacteria and microbes that attach to or clings to plants and other submerged objects in the water. Carey and the other scientists won’t be able to quantify the results until at least the end of next summer, but he has noticed preliminary changes. It seems like Elodea changes something about the food web in McKinley Lake that leads to a lower growth rate for the Coho salmon, but he can’t be sure just yet. Elodea’s effects have been studied in other parts of the world – it’s invaded lakes and ponds throughout Europe, Asia, Africa, New Zealand and Australia. In each place, it effects the environment differently because each ecosystem is unique. But its negative effect on native aquatic ecosystems and salmon growth have been widely documented. Carey’s study is the first of its kind in an Alaska native ecosystem. But once the effects of Elodea have been established by Carey and the other researchers, it just leaves them with more questions. If Elodea is harmful to fisheries and continues to spread to remote areas, moving from southern Alaska to subarctic and arctic regions, how will they be able stop and contain the spread? Some researchers at the U.S. Forest Service in Cordova, Alaska are already testing the potential use of an herbicide on established Elodea beds in the area, looking for ways to effectively kill the invasive species without leaving lasting damaging to salmon habitat. Containing the spread: To fluridone, or not to? Attempts to manage or eradicate Elodea in remote Alaskan areas would be expensive, and it would be difficult to know just where the plant had spread. “This prevention piece is just so huge here,” said Carey. “You can see it getting into some remote lake and it would just sort of be this ratchet effect of it spreading out there and we might not even notice because it’s such a remote system.” Theresa Tanner, fisheries biologist with the U.S. Forest Service in Cordova – not far from McKinley Lake – is overseeing research that could eradicate the invasive plant in contained bodies of water. Using the herbicide fluridone, an organic compound with low toxicity to animals, she is studying its effectiveness at killing Elodea when used in Alaskan ponds. Fluridone a strategy that’s been used with some success in other places, but according to Tanner, there is no data or literature on fluridone’s effects in Alaskan aquatic environments. And in an area like the Copper River Delta, a flowing water system where water levels fluctuate dramatically, it would be difficult to maintain a prescription level of the herbicide long enough to kill Elodea. “There’s three main management questions for us,” said Tanner. “What are the effects of Elodea, what are the effects of treating elodea, and can we effectively treat?” Nothing is cut-and-dry about the situation. Some studies have suggested that Elodea is positive for plankton growth, which is good for Sockeye salmon, but that it may be bad for invertebrates, which Coho salmon depend on, said Tanner. “There’s all these different situations. Nothing’s clean or easy. There is no right and wrong, bad-guy simple answer,” said Tanner. “And so, it’s teasing out and really making an informed management decision when you’re looking at the fluridone.” The chemical alone could cost more than $11 million, said Tanner, and that estimate doesn’t even include personnel costs and deployment logistics. If elodea continues to spread, that cost could be even higher. The plant spreads with ease because it is so adaptable to new conditions, making the eradication and management of the plant more problematic. It can propagate itself in a new location from just its stem – something called vegetative reproduction. “It just takes a little sprig of the stuff to be moved around and it completely re-roots,” said Tanner. The effects of Elodea and the effects of the fluridone herbicide on salmon and their Alaskan ecosystems are unknown for now, but by the end of both studies, both Tanner and Carey hope to have more answers. “It’s Alaska. This is an amazing salmon nursery. Eyak Lake alone – that’s a million-dollar fishery annually for what it produces in sockeye and silver,” said Tanner. “And that’s not the most productive system that we have.” For now, the researchers are searching for answers in the Copper River Delta and its surrounding ponds, among the thick, green, watery beds of Elodea. Definitions: Invasive species: A species that enters an environment to which it is not native and causes ecological or economic damage, according to the National Oceanic and Atmospheric Administration. Periphyton: A complex mixture of freshwater organisms such as algae, cyanobacteria and microbes that attach to or clings to plants and other submerged objects in aquatic ecosystems. Otolith: A small, oval calcium-based structure or bone (usually in threes) in the inner ear of vertebrates that are involved in processes that sense gravity and movement. Oligotrophic: Usually describing a lake, this term means that the water is low in plant nutrients like nitrogen and phosphorous but high in dissolved oxygen. Eutrophic: Usually describing a lake, this term means that the water is overly high in plant nutrients and and minerals, leading to overgrowth of plants and algae and often leads to water very low in dissolved oxygen. This is primarily due to the decomposition of die-off plants pulling oxygen molecules from the water. Phenotypic plasticity: Refers to an organism’s ability to respond to a new or unique environment in terms of changes in its behavior, morphology and physiology. Invasive plants like Elodea with phenotypic plasticity establish themselves and adapt in new places with more ease. Lentic: Organisms or habitats in still, fresh water, such as a lake. Lotic: Organisms or habitats in rapidly moving fresh water, such as a river. Macrophyte: an aquatic plant that grows in or near water and is either emergent (its growth breaks the surface of the water), submergent (growing underwater), or floating. Alizarin Complexone: A stable isotope (non-radioactive form of atoms) used as biological dye for scientific study. Macroinvertebrates: organisms with no spine that are large enough to be seen with the naked eye. Examples include flatworms, crayfish, snails, clams and insects, such as dragonflies. Many aquatic insects live as juveniles, called nymphs or larvae, in the water, and become flying insects as adults.