Water Weeds

Aquatic invasive animals are not the only species that cause problems in Tennessee and the southeastern United Sates. Invasive plants can cause just as many problems. Aquatic plants are introduced outside their native range by being transported on boat propellers and boat trailers or from home aquariums.

There are many ecological and economic problems associated with invasive plants. An overgrowth of an invasive plant can block the sun from native species, causing them to die and reducing plant biodiversity. The corresponding increase in dead plant material at the bottom of a lake or pond can result in the loss of all oxygen in the water as bacteria break down the dead plants. This process is called eutrophication. Invasive plant species can also crowd and degrade bottom habitat for fish and invertebrates.

From http://www.protectyourwaters.net/impacts.php

Many invasive plants, like Hydrilla (Hydrilla verticillata), can form large mats. These mats often jam propellers and ruin boat engines. The mat may grow so thick that the water becomes inaccessible to boaters and swimmers. Plants can also foul anglers’ equipment. Some aquatic invasive plants are vectors for diseases that impact native wildlife.

To prevent the spread of invasive plants, check, clean, and dry. Check all parts of a boat and other equipment for plant fragments. Some of these species, like Eurasian watermilfoil (Myriophyllum spicatum) can reproduce by fragmentation. One small piece of the plant will grow into a full plant. Properly clean all gear before transporting either home or to another body of water. Let all equipment dry for 48 hours before using it another area.

Read the following stories from Chattanooga Times Free Press to learn about what is being done to control populations of invasive plants in local waters.
http://www.timesfreepress.com/news/2011/may/31/waging-war-water-weeds/
http://www.timesfreepress.com/news/2011/jun/27/whacking-water-weeds/

Guest Post: First Time River Snorkeling

As an intern at TNACI, I was recently given the opportunity to perform fieldwork with some of the aquarists from the Tennessee Aquarium. We traveled to the Tellico Plains area. Here, we focused on the Little Tennessee River and the Tellico River. Our goal was to collect fish for one of the River Journey exhibits.

The first place we stopped was the Little T River. Here, we used seine nets to catch shiners and darters. We mostly caught Saffron Shiners and Warpaint Shiners as well as some Rosyside Dace. There were also numerous sightings of Rainbow Trout of all sizes, suggesting they have moved into the area and are breeding.

Saffron Shiner.  Photo by Noel Burkhead

In order to catch other fish for the exhibit, we had to snorkel in the river with small hand nets. This seemed like a difficult and odd task at first, but snorkeling in shallow rivers is very exhilarating! Using this technique we were able to catch individuals from several darter species, including eight Tangerine Darters in the Tellico River! 

Tangerine Darter.  Photo by Conservation Fisheries, Inc.

My favorite part of the experience was discovering the diverse microhabitats of these river systems and which fish tend to be found where. I never knew there were so many colors to see! If given the chance, everybody should go snorkeling in a river, it is just as amazing as exploring a coral reef in the ocean.

--Sarah Candler, TNACI Intern

When Bait Takes Over

The rivers of Tennessee and the southeastern United States are some of the most diverse ecosystems in the world, especially for invertebrates like mussels and crayfish. Crayfish are especially diverse in Tennessee, with at least 70 species inhabiting our waters. Many crayfish species are specially adapted to their environments, and many only inhabit one or two watersheds. The Nashville crayfish is found only in the Mills Creek basin in central Tennessee, while the Chickamauga crayfish is found only in the South Chickamauga Creek basin, which spans four counties in Georgia and Tennessee. These species are of greater conservation concern due to their small ranges or specialized habitat. Like many other native aquatic animals in the southeastern U.S., they are also under threat due to the introduction of invasive crayfish species.

Crayfish, also called crawdads, crawfish, or mudbugs, are commonly used as bait by commercial and recreational fishermen. They are either purchased from bait stores, or caught from the wild by anglers. Often at the end of the day, the bait is released where used, without regard to its original source. Virtually every invasive crayfish species in Tennessee has been introduced by bait bucket releases. Once introduced, non-native crayfish negatively impact ecosystems and can cause economic losses through damage to riverbanks, dams and dikes. Many invasive crayfish species directly prey on native snails, fish, and crayfish, while others eat or destroy aquatic vegetation that provides habitat and food for native fish. Many of the invasive species are very aggressive and outcompete native crayfish species for burrows or cover.



The Tennessee Wildlife Resources Agency lists six non-native crayfish species as warranting particular concern: bigclaw crayfish, Cumberland crayfish, red swamp crayfish, rusty crayfish, virile crayfish, and White River crayfish. Because these species are generalists compared to many of the native crayfish species, they can spread rapidly through a watershed if introduced. Rusty crayfish and virile crayfish have even been documented hybridizing with native species.

The biggest step you can take in preventing the introduction of invasive crayfish is to use them for bait only from the stream that you are fishing, to take only what you need, or to release bait crayfish from the same stream from which you caught them.

River Invaders

The name Asian carp is used to describe four different species of carp: grass carp, bighead carp, silver carp, and black carp. These fish were introduced in the United States in the 1970s and since that time have spread rapidly. At least one species of Asian carp is found in every state except Alaska, Maine, Montana, Rhode Island, and Vermont. They pose a major ecological threat to native aquatic wildlife and river ecosystems, as well as a significant economic threat to commercial fisheries.

All Asian carp species are native to large rivers in eastern Asia and were introduced in the U.S. to “improve” water quality. Some species, such as the grass carp, were introduced to control nuisance plant species because they eat algae and other aquatic plants. Other species, such as the black carp, eat mussels and snails and were introduced to control disease carrying invertebrates in aquaculture ponds.

From http://sportsthat.blogspot.com/2010/07/asian-carp-invasion.html

From aquaculture, Asian Carp were introduced into American rivers by illegal and intentional release, or by accidental escapes from river flood waters reaching aquaculture ponds. Once in the wild, they pose several threats to the ecosystem. Grass carp consume enormous amounts of plants. Their voracious appetite robs native fish and invertebrates of their food source. Large quantities of carp waste degrade water quality.

The two species threatening the Great Lakes are the silver and bighead carp. Millions of dollars have been spent on electric barriers, cameras, and other monitoring equipment attempting to protect the lakes. Asian carp have already caused extensive environmental and economic damage in the Mississippi and Missouri River basins. Many people have had to abandon their fishing grounds because of the presence of carp. This threatens a 7 billion dollar per year commercial and recreational fishery in the Great Lakes. Silver carp can also harm humans. When startled by boat motors, the fish (which can weigh up to 60 lbs!) leap out of the water, causing potential injury or fatality to people.



There is now concern that the extent of Asian carp’s range has increased. The flooding of the Mississippi and Missouri rivers this year may have transported some of these fish into lakes and tributaries where there are no established carp populations.

Not-So-Effective Pest Control

There are two species of mosquitofish found in the United States, western mosquitofish (Gambusia affinis) and eastern mosquitofish (Gambusia holbrooki). They are very small fishes, with adults less than 3 inches in length. As the name suggests, mosquitofish eat mosquito larvae, along with plankton, small invertebrates, and larval fish. Because of their diet, they have been widely introduced around the world to control diseases like malaria that are associated with mosquitoes.

The native range of the mosquitofish is not well known because human introductions started in the early 1900s. The two species were likely restricted to Gulf and Atlantic coastal plains and the lower Mississippi River Valley. Due to the broad spectrum of their diet and water quality tolerance, mosquitofish are habitat “generalists” that are able to flourish in a wide range of conditions. These traits, combined with their high reproductive rate and frequent dispersal by humans, have resulted in two species that are very successful invaders.



Western Mosquitofish (Gambusia affinis). From http://www.issg.org/database/image.asp?ii=1636&ic=e

Despite their small size, invasive mosquitofish can have a big impact on their environment. Introductions of mosquitofish can lead to algal blooms if they have consumed the zooplankton that keeps algae under control. They can cause populations of native fishes to go extinct through competition for food and direct aggression. They also carry parasites that infect native fish. Worst of all, research has shown that mosquitofish are no more effective at controlling mosquito populations than native mosquito predators. They can even increase the size of mosquito populations by feeding on or outcompeting the mosquito’s native predators.

Mosquitofish can be a problem here in Tennessee because they threaten the Barrens topminnow (Fundulus julisia). This fish occurs in only in three counties in Tennessee and is part of our natural heritage. Unfortunately, the larvae of the Barrens topminnow are eaten by the mosquitofish, and larger juveniles have to compete with the invasive species for food. The Tennessee Aquarium Conservation Institute is currently reintroducing Barrens topminnows to springs with where mosquitofish have been excluded in order to prevent negative impacts from this invasive species.

How did that get here?

Southeastern rivers and streams have more species of aquatic animals—fishes, mussels, turtles, and salamanders—than anywhere else in the country. Hiding in all of this diversity, however, are alien species--an animal or plant that has been introduced through human activity outside of its native range. Many species that we commonly seen in Tennessee, like bighead carp or even redbreast sunfish, are not native to this region.

Alien species may also be known as nonnative, invasive, introduced, or nuisance species. There are several ways that a species may be introduced into a waterway outside of its native range. Sometimes humans put them there on purpose, such as stocking fish that are popular for recreational and sports fishers. Sometimes nonnative species are introduced by well-intentioned people releasing fish from their home aquariums without thinking about the impact on the environment. Some introductions happen unintentionally. Commercial shipping is a major transporter of invasive species in U.S. bays, major rivers, and the Great Lakes. Ships will take in water, called ballast water, in one area to maintain balance as they travel across oceans and rivers. There are almost always small organisms in that water. When ships reach their destination, they release the water, and with it, any organisms that were taken in at the original port. Many shipping ports now have regulations about releasing ballast water, but this has historically been a major pathway for introductions of nuisance species in the Great Lakes.

Over the next few weeks, we will highlight some different invasive freshwater species and their impact on both humans and the environment. Most are species that can be found in the Chattanooga area, Tennessee, and the southeastern United States. Stay tuned!

Redbreast sunfish (Lepomis auritus) is one of the many invasive aquatic species found in Tennessee waterways. From http://fish.dnr.cornell.edu/nyfish/Centrarchidae/redbreast_sunfish.html