The best explanation of how invasive plants and animals are damaging to ecosystems and us human animals comes from the Yukon Invasive Species Council.................... "Invasive species are the second greatest threat to biodiversity after habitat loss"................"Across the Americas(and throughout the world), many invasives are responsible for de-stabilizing habitat damage, loss of subsistence resources, and economic loss"................. "Invasive species are defined as organisms (plant, animal, fungus, or bacterium) that have negative effects on a region's economy, environment, or public health"..............."In the Santa Monica Mountains of Los Angeles and across southern California, invasive red swamp crayfish devastate native wildlife such as the endangered Red-Legged Frog, throwing the entire SoCal ecosystem out of kilter"........"Red swamp crayfish are originally from the southeastern and central USA........... "Folks dumping their aquarium crayfish "pets" in our streams and waterways over the years have created a "frankenstein ecological nightmare"..............."Female crayfish reproduce about once a year in their native central and southeastern states"................ "In Southern California, because of the warmer climate, females can reproduce two or more times a year".............."One female crayfish can deliver up to 600 eggs".............. "In the Santa Monica Mountains, the small crustaceans resembling small lobsters have had a huge debilitating impact on the native populations of the California newt, the arroyo chub, and the red-legged and Pacific tree frogs".......... "And since crayfish burrow into the streambed, they can worsen water quality and cause problems with native foliage that grows next to the creeks"................."We Humans are also adversely impacted by the presence of the Crayfish"............... "Mosquito populations are kept in check by dragonfly nymphs, which voraciously consume their aquatic larvae".............'The crayfish disrupt that predator-prey relationship, killing and driving dragonfly nymphs from waterways"..............At the moment, other than mobilizing youth and conservation groups to hand pick the crayfish out of our streams, there does not appear to be a way to rid SoCal of this scourge

https://phys.org/news/2018-08-invasive-crayfish-mosquitoes-disease-southern.html

Invasive crayfish lead to more mosquitoes and risk of disease in Southern California

August 7, 2018, University of California, Los Angeles

Invasive red swamp crayfish are a serious problem in the Santa Monica Mountains and other parts of Southern California. They devastate native wildlife, including threatened species such as the California red-legged frog, throwing off the natural balance of ecosystems

Invasive, non-native Crayfish

They also pose a threat to people, according to a new paper in the journal Conservation Biology. The study is based on field research in the Santa Monica Mountains and lab experiments at UCLA La Kretz Center for California Conservation Science.

Mosquitos are notorious vectors that spread diseases such as malaria, Zika and West Nile virus. In the mountains, mosquito populations are kept in check by dragonfly nymphs, which voraciously consume their aquatic larvae. But invasive crayfish disrupt that predator-prey relationship, killing and driving dragonfly nymphs from waterways. And while crayfish also consume mosquito larvae, they're simply not as good at it, the researchers found.

California Red-Legged Frog

"A lot of people don't know this but before dragonflies are flying around and beautiful, they actually are these voracious predators in streams and ponds," said Gary Bucciarelli, a UCLA conservation biologist and the paper's lead author. "They do a great job of preying on other invertebrates in the streams we work on."

After noticing that streams with the crayfish had almost no dragonfly nymphs and lots of mosquito larvae, Bucciarelli and other scientists decided to investigate further. They looked at 13 streams in the Santa Monica Mountains.

The Range of the California Red-Legged Frog(orange shading)

"There tended to be sites where we found a ton of mosquito larvae and very few dragonfly nymphs," Bucciarelli said. "And in streams where there were no crayfish, we found the opposite pattern—a ton of dragonfly nymphs and no mosquito larvae."

They took their research to the next step with controlled experiments in a laboratory. They set up tanks with only crayfish, tanks with only dragonfly nymphs and tanks that had both. The dragonfly nymphs alone wiped out mosquito larvae, while crayfish were much less efficient. And in tanks with both, the crayfish disrupted the predator-prey relationship so severely that there were as many mosquito larvae as there were in the tanks with only crayfish.

"The dragonfly nymphs don't know what to do with crayfish," Bucciarelli said. "We observed strange behaviors. They were even resting on their claws. The presence of crayfish disrupts their behavior and essentially turns them into worthless predators."

Santa Monica Mountains Recreation Area(south of Calabasas,
Agoura and Westlake Village on map)

The findings have implications beyond Southern California. The red swamp crayfish is a globally invasive species that affects every continent except Antarctica. In many locations, Bucciarelli said, the crayfish harm entire ecosystems by disrupting patterns of predators and prey—just as they do with dragonfly nymphs and mosquito larvae.

The Las Virgenes–Triunfo Joint Powers Authority, which provides wastewater services, recycled water and other services within the Malibu Creek watershed, partnered with UCLA, Pepperdine University and Mountains Restoration Trust on today's research. The project is part of a long-term effort to understand the invasive crayfish and eliminate or reduce their numbers as much as possible. The original intent was to protect endangered and threatened species, but today's findings reveal a human impact that hasn't previously been examined, said Robert Fisher, a U.S. Geological Survey research biologist and co-author of the study.

"We recovered five miles of Malibu watershed. Just by removing the crayfish, not doing anything else, red-legged frogs are returning to their natural habitat," Fisher said. "Not everyone cares about that response, but they care about the human health aspects—preventing malaria, encephalitis and dengue fever."

Climate change appears to be making the problem worse, Fisher added. The red swamp crayfish comes from places in the Southeast United States that are hot or at least warm all year long. As temperatures increase with global warming, local habitat becomes more suitable to the pests.

Brad Shaffer, a UCLA conservation biologist and director of the La Kretz Center, said today's research is part of a larger effort to work across disciplines to address environmental problems.

Santa Monica Mountains National Recreational Area

"We blend field conservation biology, human health and the role of invasive species," Shaffer said. "It's what conservation biology should be—undergraduate students, wildlife professionals, government biologists and university researchers coming together to figure out how species fit together in our human-modified world."

More information: Gary M. Bucciarelli et al. Assessing effects of non-native crayfish on mosquito survival, Conservation Biology (2018). DOI: 10.1111/cobi.13198 

Journal reference: Conservation Biology  Provided by: University of California, Los Angeles more at: https://phys.org/news/2018-08-invasive-crayfish-mosquitoes-disease-southern.html#jCp