Kayaking to assess invasive crayfish species
This past fall, Virginia Tech researcher Bryan Brown took to the rushing waters of the New River on kayak for 17 days to conduct an invasive crayfish species assessment.
“It’s amazing fun getting out there and doing science out of a kayak,” said Brown, associate professor in the Department of Biological Sciences in the College of Science.
Brown studies large-scale community ecology. His work focuses on how multiple species interact in aquatic habitats and how those interactions are altered by changing environmental conditions.
For his kayaking trip, Brown studied two species of invasive crayfish that have been working their way east and south through the West Virginia, Virginia, and North Carolina waterways.
“Crayfish are among some of the nastiest invaders in the world, in terms of aquatic species. Researchers have created maps that show where these crayfish may be found, but there is not enough information to create a continuous map of the species’ distribution,” said Brown, an affiliated faculty member of the Global Change Center, housed within the Fralin Life Science Institute.
Brown’s goal for this trip was to fill in these gaps. To address this problem, Brown planned a 17-day kayaking trip on the New River. His adventure began in Boone, North Carolina, and concluded at Bluestone Lake State Park in West Virginia, where the Bluestone River meets the New River.
Brown’s trip was first delayed by Hurricane Florence. Geared up and ready to go, Brown was once again delayed as Hurricane Michael hit the southeast and caused the highest water levels in 40 years. The annual median water levels are usually 1,650 cubic feet per second in the New River; they rose to 110,000 cubic feet per second after Hurricane Michael.
Ready to finally start his trip, Brown ventured off in his 12-foot kayak with 17 days’ worth of supplies. The elevated water levels carried him down the river at 7.5 mph — 3.5 mph faster than usual. The water pushed Brown onto a low river crossing, toppling his hefty kayak and causing him to lose his supplies and phone.
Brown paused his journey and returned home to devise a new plan. He redesigned his itinerary to include several trips of two to three days each, stretching from North Carolina to West Virginia. This adjustment allowed him to pinpoint exactly where he wanted to sample for crayfish. Brown finally started his data collection in mid-October.
The study focused on two invasive species of crayfish: Faxonius cristavarius, the spiny stream crayfish, and Faxonius virilis, the northern crayfish.
Invasive species are organisms that are not native to an area and can upset the balance of the ecosystem they invade. Brown investigated how these invaders disrupt the relationships between native crayfish and their symbionts, in this case worms. The worms and crayfish live in symbiosis with one another — the worms feed on parasites and keep the crayfish’s exoskeleton clean, especially its gills. In exchange, the worms get food, protection, and habitat.
Crayfish are critically important to aquatic ecosystems. They are omnivorous and feed on decomposing organic material and just about any fish or insect they can catch. Additionally, crayfish are bioturbators, meaning that they live in substrate and move sediment around when they forage. Their actions actually reduce sedimentation in areas, because they kick material up into the water column, which gets carried downstream.
Brown posed several questions before embarking on his trip: When the crayfish invade, do they bring their own symbionts or rely on native ones? Does bringing their own symbionts allow them to invade better than without them, or does disrupting native symbionts actually increase their ability to invade?
What Brown does know, however, is that invaders are disrupting the relationships between natives and symbionts. In a study started with his former master’s student, Spencer Bell, they found that that invaded areas show decreased symbiont levels — half of what they should be.
For the kayaking trip, Brown identified 16 sampling sites. The spiny stream crayfish is already an established invader, but Brown wanted to see how prevalent it was in the river. On the other hand, the northern crayfish is still spreading — but just how far east and south? The farthest south Brown identified the species was in Eggleston, on the New River, but they are also found in Blacksburg’s Stroubles Creek.
The two invasive crayfish are far from home. The aptly named northern crayfish originates from Canada and the northern midwest. They are randomly found all over the map, so it is hypothesized that these invaders were introduced by fishermen who use them as bait for bass fishing.
The spiny stream crayfish, however, poses a mystery. They are not as invasive as much as they are what Brown calls “native range expanders.” This species has grown outside of its historic range of Ohio, West Virginia, and Kentucky. Brown is working with a team of researchers to address why this is happening and to bring more attention to native range expanders.
One working theory is that the spiny stream crayfish may gain an advantage from disrupting symbionts. “They are the worst hosts that we know of. They have very few symbionts on them compared to tens and twenties on the native species,” said Brown. “They are very poor hosts and have a different suite of behaviors in terms of their responses to symbionts.”
This may be because the spiny stream crayfish’s hemolymph — the equivalent for blood in most invertebrates — has antimicrobial properties. It could be that this species does not need symbionts, because they have a natural ability to reduce infection.
However, native crayfish species rely on symbionts. Brown is currently working on a paper that demonstrates the importance of symbionts by enclosing crayfish in flow-through chambers placed in streams. By not including symbionts in the chambers, the crayfish were unable to fully do their jobs, changing the ecology of the stream.
Brown will use the information he gained from his kayaking trip and assessment to apply for a National Science Foundation grant in hopes to expand his study area and further document the invasive species’ effects on aquatic systems.