Grass Carps Are Invasive Alien Species In California That Destroy Ecosystems By Eating A Very Large Amount Of Plant Material

Also known as a non-native species, invasive species are species that are originally from a certain area but are introduced in a new environment either by the accidental, or deliberate actions of humans and so, are categorized as biological pollutants. These invasive species are so dangerous because they lack predators, so it is easy for them to dominate, and outcompete native species populations. Sometimes, non-native species can completely change and transform ecosystems. The Grass Carp is one of these invasive species, and is found in California.

They are considered invasive because they “have a ravenous appetite for plants, and can quickly reduce or eliminate large quantities of aquatic vegetation from bodies of water. This can lead to the alteration or loss of habitat for native species, reduction in food availability for waterfowl, and increased occurrences of algae blooms” (California Department of Fish and Wildlife). While feeding, grass carp disrupt sediment deposit and muddy waters, which can impact reproducing habitats for indigenous fish.

They have also been known to be the primary vector for Asian Tapeworms, and carry viruses that are infectious to other fish (California Department of Fish and Wildlife).

Yielding over five million tons per year, the Grass Carp has the largest reported production of hydroponics yearly (Wikivisually, 2016). The Grass Carp is originally found in eastern Asia, and it normally ranges from the northern part of Vietnam to the Amur River, which is on the border between China and Siberia (Vassili Group). It was introduced in the United States, and parts of Europe for marine foliage control, but it was originally farmed, and used in China for a food source (Vassili Group).

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“In 1963, grass carp were introduced into the U.S. for aquaculture in Arkansas. They were later released into an Arkansas lake and the Arkansas River in the early 1970s and quickly spread to the Mississippi River drainage and established reproducing populations” (California Department of Fish and Wildlife). In the United States, there is still a distribution problem because of them escaping in open waters, illegal, and legal stocking for weed control, and for aquaculture and research operations (California Department of Fish and Wildlife). Grass Carp cannot be shipped, imported, or possessed without a authorized permit because they are on California’s list of restricted animals (California Department of Fish and Wildlife).

The Grass Carp grazes, and feeds on vegetation that is found in shallower waters, and mostly near the surface of the water, which is more accessible (Weeks, Hill, 2014). The new growth of submersed plants is the ideal diet of the Grass Carp. Larger Grass Carps prefer Hydrilla, whereas small one’s prefer musk grass. This is because their plant feeding preference is dependent on their size (Weeks, Hill, 2014). However, the grass carp is not picky at at all, and is sort of a generalist, meaning , that in the absence of the desired plant, they will feed on most other types of aquatic weeds (Weeks, Hill, 2014). This is why they cause so many problems. Grass carp even have been seen to feed on terrestrial plants that are hanging over the water. There are about five most-preferred plant species that Grass Carp will eat (Weeks, Hill, 2014). In order of preference, they are; hydrilla, musk grass, and Brazilian elodea (Weeks, Hill, 2014).

Grass carp eat by grinding vegetation, because they have comb-like teeth, which are located in their throat, since they do not have normal teeth in their jaws (Weeks, Hill, 2014). In fact, their scientific name means “distinctive comb pharyngeal teeth.” When Grass Carp are small, they will usually only eat the leaves off of plants, but as they start to grow in size, they will eat both leaves and stems as grown adults (Weeks, Hill, 2014). An adult grass carp will devour its body weight in hydrilla every day, but only in water that is warm enough for them(68 °F or 20 °C) (Weeks, Hill, 2014). The conversion to animal protein is limited, even though adult grass carp consume a huge amount plant material, (Weeks, Hill, 2014). For every one pound that they weigh, they must eat about five or six pounds of dry Hydrilla in order to get the appropriate amount of protein to sustain them (Weeks, Hill, 2014).

If the aquatic vegetation is reduced in a specific area, then the ecosystem that has been stocked with the grass carp will change drastically in several ways (Weeks, Hill, 2014). “Phytoplankton will increase and cause a decrease in water clarity, fish species that are reliant on vegetation will decline and may be eliminated from the ecosystem, and species that feed on phytoplankton will increase in number” (Weeks, Hill, 2014). Grass Carp’s create harsh competition for food, significant changes in the configuration of, phytoplankton, invertebrate, and macrophyte communities (United States Department of Agriculture, 2018). They also modify preferred habitat of other species, hinder with the reproduction of other fishes, decrease habitats, and refuge for other fishes (United States Department of Agriculture, 2018). By prompting changes in plant, fish, and invertebrate communities, they have drastically transformed the food web and trophic organization of aquatic ecosystems (United States Department of Agriculture, 2018).

Many studies have been performed to show how grass carp significantly decrease the amount of plant biomass, and increase the amount of chlorophyll in the water. Although grass carp are much praised in the Imperial Valley, they have been much feared elsewhere. Environmentalists have worried that the fish could invade waterways and drive native fish into extinction by devouring their food source. Today, only sterile Grass Carp are used. Sterile fish were developed by exposing eggs to heat stress or pressure. The stress that is presented, (either heat or pressure) causes each egg to preserve an extra set of chromosomes and no longer become diploid, but instead become triploid (Weeks, Hill, 2014).

The first condition that needs to be met when initiating a biological control agent is typically host specificity (Weeks, Hill, 2014). Hence, it is crucial that lakes, or other bodies of water are not overstocked because the fish are challenging to eliminate once they have been introduced (Weeks, Hill, 2014). “Grass carp must only be stocked into closed water bodies. In open water bodies, any canals, channels or streams leading into other areas must be blocked with barriers to prevent fish escape. The barriers need to have a fine enough mesh to prevent the smallest fish from swimming through and must be high enough so that the fish cannot jump over” (Weeks, Hill, 2014).

Grass carp supervising could be accomplished by using electrofishing along splits, mesh netting or by using hydroacoustics (Weeks, Hill, 2014). Hydroacoustic techniques are non-invasive but do not specifically identify and target a certain species, so it might be difficult to use (Weeks, Hill, 2014). If you are thinking about stocking Grass Carp, you must consider that they will ultimately need to be taken out once control of the aquatic vegetation have been reached (Weeks, Hill, 2014). Removal though, is not an easy task, without killing all fish in the body of water, and it demands a permit (Weeks, Hill, 2014).

Though it may seem like nothing can be done about this, there are some things that can be done to solve this invasive species problem. One way is by using an electric shock, which involves a couple hundred feet of canal water that has been electrified (Hasler, 2010). This is what stands between a group of Grass Carp, and the open waters where they can escape (Hasler, 2010). “The Dispersal Barrier System first went online in 2002, when a low-voltage technology demonstration called Barrier I was activated. In 2009, Barrier IIA, went live, and it now operates at a voltage (2 volts per inch) powerful enough to stop a human heart. A third barrier, meant to provide redundancy, is currently in the final stages of construction and safety testing” (Hasler, 2010). The fish appear to be floating just below the electrified expanse of water, despite the detection of Grass Carp DNA outside the electric barriers (Hasler, 2010). To prevent that from happening a blockade will be built.

The blockades are comprised predominantly of chain-link fencing and concrete barriers, and fluctuating in height from about 4 to 6 feet (Hasler, 2010). Grass carp are tremendously sensitive to sound frequencies stretching from about 750 to 1500 Hz (Hasler, 2010). This is caused, because the Carp’s have a series of small bones joining the swimming bladder to the inner ear “Spooked by the sound of revving boat motors, carp have been known to leap several feet in the air, causing damage to boats and boaters alike” (Hasler, 2010). “Researchers at the Illinois River Research Station, run by the University of Illinois, are testing a technology called a Sound-Bubble-Strobe (SBS) Light Barrier, which sends Asian carp downstream using LED lights and high-frequency sound. Speakers project a cycle of high-pitched whooping noises, increasing from 500 to 2000 Hz, across a curtain of bubbles that rise from an aerating device strung across the riverbed” (Hasler, 2010).

In conclusion, Grass Carps are invasive species found in California. They are alien species, because they do not originate from California, and they destroy ecosystems by eating a very large amount of plant material, which affects other organisms by altering the food web. Although, their plant clearing ability might be useful for certain circumstances, it is usually destructive. Luckily, there are some ways to avoid this, and get rid of them if they are already a problem. For example, you can sound them out by using frequencies to spook them, and another way is to put up a blockade to keep them out. In the future, maybe we can find ways to stop these kinds of species before they become invasive.