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

August 7, 2018, University of California, Los Angeles
The study is part of a long-term effort to understand the invasive crayfish and eliminate or reduce their numbers. Credit: U.S. Geological Survey

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.

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.

"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.

Invasive crayfish lead to more mosquitoes and risk of disease in Southern California
Dragonfly nymph. Credit: U.S. Geological Survey
"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."

The findings have implications beyond Southern California. The red swamp crayfish is a globally 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 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.

Invasive crayfish lead to more mosquitoes and risk of disease in Southern California
Red-legged frog. Credit: U.S. Geological Survey
"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 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.

"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."

Explore further: Invasive marbled crayfish found in Narva power plant cooling canal

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

Related Stories

Crayfish may help restore dirty streams, study finds

April 21, 2016

While macroinvertebrates are a tasty food source for crayfish, a new study reveals a surprising finding: When crayfish were present in in-stream experimental enclosures, macroinvertebrate density was higher, not lower.

Crayfish study provides complicated web of interactions

February 18, 2014

Managing the damage and impact of non-native or invasive species costs the UK nearly £2 bn per year. The UK has seven species of crayfish with established populations – only one is a native species.

Dragonfly enzymes point to larger evolutionary dynamics

May 24, 2018

Although evolution has left dragonflies virtually unchanged for roughly 300 million years, new research by a UTM biologist reveals that understanding small physiological activities in these insects could reveal a deeper understanding ...

Recommended for you

Birds startled by moving sticks

October 23, 2018

Do animals—like humans—divide the world into things that move and things that don't? Are they surprised if an apparently inanimate object jumps to life?

Chimpanzees sniff out strangers and family members

October 23, 2018

Chemical communication is widely used in the animal kingdom to convey social information. For example, animals use olfactory cues to recognize group or family members, or to choose genetically suitable mates. In contrast ...

Breakthrough test screens for all known bacterial infections

October 23, 2018

Scientists at the Center for Infection and Immunity (CII) in the Columbia University Mailman School of Public Health have developed the first diagnostic platform that can simultaneously screen for all known human pathogenic ...

Researchers have discovered a new cell structure

October 23, 2018

A new structure in human cells has been discovered by researchers at Karolinska Institutet in Sweden in collaboration with colleagues in the U.K. The structure is a new type of protein complex that the cell uses to attach ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Iochroma
5 / 5 (1) Aug 07, 2018
This crayfish is also responsible for weakening dikes in the Sacramento River Delta.
Whart1984
Aug 07, 2018
This comment has been removed by a moderator.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.