Eagles may get exposed to a neurotoxin through their prey. MIKE MARTIN
By Erik Stokstad — Mar. 25, 2021
More than 25 years ago, biologists in Arkansas began to report dozens of bald eagles paralyzed, convulsing, or dead. Their brains were pocked with lesions never seen before in eagles. The disease was soon found in other birds across the southeastern United States. Eventually, researchers linked the deaths to a new species of cyanobacteria growing on an invasive aquatic weed that is spreading across the country. The problem persists, with the disease detected regularly in a few birds, yet the culprit’s chemical weapon has remained unknown.
Today in Science, a team identifies a novel neurotoxin produced by the cyanobacteria and shows that it harms not just birds, but fish and invertebrates, too. “This research is a very, very impressive piece of scientific detective work,” says microbiologist Susanna Wood of the Cawthron Institute. An unusual feature of the toxic molecule is the presence of bromine, which is scarce in lakes and rarely found in cyanobacteria. One possible explanation: the cyanobacteria produce the toxin from a bromide-containing herbicide that lake managers use to control the weed.
The discovery highlights the threat of toxic cyanobacteria that grow in sediment and on plants, Wood says, where routine water quality monitoring might miss them. The finding also equips researchers to survey lakes, wildlife, and other cyanobacteria for the new toxin. “It will be very useful,” says Judy Westrick, a chemist who studies cyanobacterial toxins at Wayne State University and was not involved in the new research. “I started jumping because I got so excited.”
Wildlife biologists with U.S. Geological Survey and local institutions first detected the eagles’ brain disease, now called vacuolar myelinopathy, at DeGray Lake in Arkansas in late 1994. They soon learned that coots and owls at the lake were dying with similar brain lesions. The researchers ruled out industrial pollutants and infectious disease, and they couldn’t find any algal toxins in the water. Then funding ran out, and the scientists turned to other projects.
But Susan Wilde, an aquatic ecologist at the University of Georgia, Athens, persisted, with intermittent funding. “I just had a lot of colleagues and graduate students that were self-propelled to work on this.” Birds were dying at lakes and reservoirs throughout the southeast, and at every lake her team visited, they found Hydrilla verticillata, a tough and fast-growing invasive plant. In 2001, Wilde noticed dark spots on the underside of the leaves. Back in the lab, she put a sample under a microscope and shone light that makes cyanobacteria glow red. The whole leaf lit up. “I was running around the hallways,” Wilde recalls. “It was kind of a eureka moment.” The cyanobacterium was a new species, which Wilde named Aetokthonos hydrillicola in 2014. She suspected it was producing a neurotoxin.
To confirm that hunch, Wilde and colleagues fed hydrilla to mallards in the lab. Only those that ate leaves harboring the cyanobacteria developed brain lesions. Next, a group led by Timo Niedermeyer, a natural products chemist at Martin Luther University Halle-Wittenberg, figured out how to culture the cyanobacterium and initially found that the lab-grown strain did not cause lesions in chickens. “Huge disappointment,” he recalls. But when they added bromide salts to the culture medium, the cyanobacteria began to produce the neurotoxin. In further tests, Wilde and colleagues found that the toxin also kills fish, insects, and worms. “This is a really potent neurotoxin, even at fairly low levels,” she says. Wilde suspects mammals are also vulnerable; her colleagues hope to test the compound on mice.
Niedermeyer’s lab discovered the neurotoxin was fat-soluble, which is unusual for cyanobacterial toxins and suggests it can accumulate in tissues. Fish and birds are exposed when they eat hydrilla coated with the new species of cyanobacteria, and then the toxin may move through the food web as eagles and owls consume afflicted prey. “If verified, bioaccumulation has important consequences to the whole ecosystem and human health” if people consume toxin-contaminated fish or waterfowl, says Kaarina Sivonen, a microbiologist at the University of Helsinki.
The cyanobacterium appears to get the bromide it needs to make the toxin from hydrilla, which can concentrate bromide from lake sediment in its leaves. Bromides are rare in freshwater, but they could be eroding from rocks, or they might originate from coal-fired power plants. Other sources could include brominated flame retardants, fracking fluids, and road salt. Wilde suspects one local source might be an herbicide, diquat dibromide, that is used to kill hydrilla.
Wilde points to recent success managing the weed without chemicals, by stocking lakes with fish that eat hydrilla. Although grass carp are not desirable for fishing, using sterile carp would ensure the population would die out once its work was done. The Army Corps of Engineers has already released the fish into a reservoir on the border of Georgia and South Carolina, where they removed the hydrilla. Since then, no more sick eagles have been found.
Saving the birds from the neurotoxin will be a long fight, however, because both hydrilla and the cyanobacteria are exceptionally hardy. The invasive plant is likely to continue to be spread by boats, researchers say, and perhaps also migrating birds. “We should expect the cyanobacterium to follow,” says George Bullerjahn, a microbiologist at Bowling Green State University, “and the threat of toxicity to become a broader issue.”
The 116-acre Comal Park in Canyon Lake, famous for its swim beach, reopens on Saturday, May 16 with improved lake access.
Today’s announcement follows a ‘soft’ opening over the weekend, when the Water Oriented Recreation of Comal County (WORD) tested its social-distancing methods on residents who signed up for free access.
The park will be limited to 50-percent capacity or 200 cars. The entrance fee is $10 per vehicle. Hours of operation are 10 a.m. to 6 p.m. Comal Park is first-come, first-served. WORD does not accept reservations.
Social distancing is mandatory.
WORD has instituted sanitizing procedures for bathrooms and touchpoints but cannot guarantee that all surfaces will be sanitized at all times.
WORD leased the park from the U.S. Army Corps of Engineers (USACE) in March. The park remained closed while WORD doubled the size of its swim beach; added a sand-beach section; added a sand volleyball court; built a non-regulation soccer field; installed 60 picnic table sites with grills; and added four washer pits.
The playground remains closed although WORD earmarked $75,000 for playground upgrades earlier this year.
Comal Park is located on the south shore of Canyon Lake near Startzville at 1178 Comal Park Rd., Canyon Lake. It also features two boat ramps.
According to USACE Natural Resource Specialist Samuell Price, Boat Ramp #3 is very shallow and closes earlier than other ramps do when lake levels are low. Boat Ramp #4 is deeper.
He said both ramps are good to launch from — wide, with plenty of space for maneuvering. Both ramps have docks.
For more information and to see a complete set of park rules, click here.
San Antonians now have access to a new segment of the Greenway Trails System that’s been in the works since 2018.
San Antonio Parks and Recreation announced this week that the Maverick Creek Greenway Trail is now open, expanding the Greenway Trails System with nearly a mile of walkable and bikeable path.
The trailhead is located at 13620 Babcock Rd., with the .7-mile trail running along Maverick Creek down Babcock Road between UTSA Boulevard and Hausman Road, eventually connecting with the Leon Creek Greenway.
The new trail, which the parks and rec department began construction on last summer, includes a stone-bedecked outdoor amphitheater, as well as playgrounds, restrooms, and a water fountain.
With the trail opening, San Antonio Parks and Recreation also notes that despite Texas Gov. Greg Abbott’s recent lifting of the mask mandate, “face coverings will continue to be required in City of San Antonio facilities,” including the more than 250 city-owned parks the department operates and maintains.
The new trail is one of several green spaces opening recently or planned for San Antonio. In February, the city revealed construction would begin this fall on Civic Park, the biggest of a three-park project for the Hemisfair urban park district. And thanks to a $1 million donation, the Hemisfair is also adding Peggy Mays Garden, with construction on that project starting in late 2021.
Perhaps the most significant of park projects planned for San Antonio is the 100-mile network of trails known as the Great Springs Project, which will connect San Antonio to Austin along the area’s waterways. That project is expected to be completed this summer or fall.
What are some of the major challenges to conservation and biodiversity in Texas? Top issues include habitat loss and fragmentation, limited water for environmental flows, invasive species and climate change.
Changing Demands on Land Resources
Human population growth and resulting land fragmentation, or the division of single ownership properties into two or more parcels, have had profound effects on the Texas landscape. Changing land use and fragmentation alters natural habitats, which can threaten the viability of those habitats and sustainability of wildlife populations. Such changes will increase pressures on natural resources throughout the state, especially near growing metropolitan areas.
Non-native plant and animal species that are introduced either by design or by accident can cause unintended harmful consequences. Non-native species may become invasive, spreading rapidly, displacing native species and threatening community relationships that are necessary to sustain the aquatic environment. Some examples of undesirable or noxious non-native invasive species include salt cedar, Chinese tallow, Chinaberry, Privet, K-R bluestem (also known as Mediterranean bluestem), Japanese honeysuckle, and giant reed. Chinese tallow has invaded woodlands and coastal prairies; left unchecked, the invasion changes these diverse habitats into practical monocultures, reducing diversity and habitat integrity for native plants and animals. Introduced grass species can create monocultures devoid of quality wildlife forage and of limited useful habitat for young ground nesting birds and burrowing small mammals. For some ground dwelling birds like quail, dense turf-type grasses create a barrier to movement; in that way, their habitat is functionally fragmented. Through improved range management techniques, they can be significantly reduced or controlled to benefit water quality and quantity as well as wildlife habitat. Imported red fire ants in eastern Texas have had profound, if not fully understood, adverse impacts on many wildlife species. Eighteen non-native fish species have been documented in Texas as well as a number of snail and bi-valve species. Some have had an extremely negative impact on native fish communities. Further, great effort and financial resources have been expended to control invasive aquatic plants such as water hyacinth, hydrilla and giant salvinia, which have negatively affected native freshwater communities.
Overgrazing and Fire Suppression
Improper grazing and fire suppression have contributed to a drastic alteration of the native landscape. Improper grazing results in soil erosion, decreased diversity in forage and cover for nesting as well as other needs of wildlife. In addition, fire suppression has caused native grasslands, savannahs and open woodlands to become overgrown with thickets of woody species.
Reduced Water Quality
Point source and nonpoint source pollution threaten native fish and wildlife species that rely on clean water. Water that will not support fish and wildlife will not support human needs either. In the next decade, pollutant concentrations in rivers and streams may increase to a point where they have a detrimental effect on aquatic life including low oxygen, harmful algal growth and fish kills.
Reduced Water Quantity
As the population grows and water demands increase, water flow in rivers and streams, or instream flow, may decrease. Decreased or altered water quantity will affect the ecosystems, habitats and wildlife that depend on the natural flow regime of the stream or river. For example, groundwater withdrawals, reservoir operations and water diversions make rivers, streams and springs and the fish and wildlife resource they support exceptionally vulnerable to the effects of drought. All bays and estuaries have great commercial, recreational and conservation benefits. The greatest long-term threat to the health and productivity of bays is diminished freshwater inflows.
Limited Understanding of Complex Natural Systems
Research is a critical component of natural resource conservation. Without reliable knowledge and rigorous scientific inquiry, scientists cannot make informed conservation decisions. For instance, some principles of wildlife ecology, such as the early research of edge effects on wildlife, have since been found to inadequately describe natural systems. The decision making process at TPWD must remain grounded in the best science available to assure that policy development, regulatory action and resource management are accurate and effective.
TPWD encourages private land stewardship, expanded research and monitoring of habitats and species, and exploring partnerships and strategies to mitigate impacts.
The Texas Wildlife Action Plan: Texas Parks and Wildlife Department, with input from partners, stakeholders and the public, completed the Texas Wildlife Action Plan in September 2005. The U.S. Fish and Wildlife Service approved the Plan in early 2006. State Wildlife Action Plans are being created by every state to prevent species from being federally “listed” as threatened or endangered, conserving wildlife and natural places and enhancing our quality of life. The agency and our partners have been implementing elements of the Plan and the Plan will be revised in 2010. Information gathered through action on the conservation priorities will be key to adapting and revising the plan to reflect current conservation needs.
As communities grow, state wildlife plans will help fulfill our responsibility to conserve wildlife and the places they live for future generations. The State Wildlife Plans are not only addressing unmet wildlife conservation needs, they are also leading to a new era of coordinated strategic planning to better identify problems and solutions on a regional and nationwide basis.