Invasive Species of California

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Aquatic Invasive Species

Quagga and Zebra Mussels

Invasive quagga and zebra mussels are a major threat to freshwater ecosystems. They are small bivalves that: reproduce rapidly, deplete nutrients, jeopardize power and water infrastructures, damage ecosystems, and destroy recreational areas. The first confirmed record of Zebra mussels in California occurred at San Justo Reservoir on January 10, 2008[1]. Quagga and zebra mussels continue to spread and have infested 39 water bodies throughout the state. A map of all infested waters can be found here. The Invasive Species Program's goal is to reduce the negative effects of these two species of mussel in the waterways of California. The California Department of Fish and Wildlife (CDFW) is involved in efforts to prevent the introduction of these species into the state, detect and respond to introductions when they occur, and prevent the spread of invasive species that have become established. Boaters are required to have their watercrafts inspected and cleaned at specific check stations around the state. For information on boating restrictions and inspections please contact the waterbody manager directly. [2] See Zebra/Quagga mussels here.

New Zealand Mudsnails (Potamopyrgus antipodarum)

New Zealand Mudsnails (NZMS) were likely introduced in Idaho and brought west from shipments of sportfish and their eggs. They are a vigorous invasive species and are becoming abundant in California's Central Coast. See more information at Invasive Invertebrates of the Central Coast.

Asian Clam (Corbicula fluminea)

Common across the entire country, the Asian Clam has made its way to California's Central Coast. See Invasive Invertebrates of the Central Coast for more information.

Grass Carp (Ctenopharyngodon idella)

Grass Carp are the staple invasive fish in California [3]. In the 1960s, they were used for aquaculture, but were soon released into natural areas [4]. Grass Carp prefer deep, warm water bodies [4]. They have voracious appetites and will readily eat much of the vegetation in lentic water bodies. When the carp remove vegetation from the water bodies, there is less food for native fish, and the increased water clarity encourages algal blooms which can kill everything in the water [4]. Grass Carp also carry Asian tapeworms, which can harm and kill native fish species [5]. Report sightings of the Grass Carp to the CDFW. See a Grass Carp here.


Giant Reed (Arundo donax)

The Giant Reed was introduced to keep riparian areas stable, but they have become successful invasive species and kill off other plants. See more at Invasive Plants of the Central Coast.

Iceplant (Carpobrotus edulis)

Iceplant was introduced from Africa to help stabilize soil. It is common in California's Central Coast. See more at Invasive Plants of the Central Coast.

English/Common Ivy (Hedera helix)

The Common Ivy is a well-known invasive species, given the invasive rank of "high" from the California Invasive Plant Council. The ivy is known to grow rapidly and take nutrients before other native plants can [6]. The plant causes no major harm to humans (minor dermatitis), but competes with other plants by wrapping around them or growing above them. Saplings and young plants are at a disadvantage especially, because they are denied sunlight and killed off [7] . The Common Ivy is a hardy plant with leaves covered in a waxy secretion, making traditional herbicides almost ineffective towards it. Keep all ivy trimmed to prevent its over-spreading. See English Ivy here.

Spanish Broom (Spartium junceum)

Spanish Broom is a tall, woody shrub that spreads quickly once it colonizes an area. The rapid colonization prevents native flowers and shrubs from growing [8]. Spanish Broom does not provide nutrients for many organisms, as it consists of mostly dead wood when it is mature. Two species of beetle (Bruchidius villosus and Exapion fuscirostre) have the potential to be used as biological controls to keep Spanish Broom numbers down because they feed on the plant and its seeds. See a Spanish Broom.

Barb goatgrass (Aegilops triuncialis)

Barb goatgrass was brought to America from Europe and Asia, and quickly spread in grassy habitats. The grass is known to be a noxious weed and is unpalatable to most livestock. Barb goatgrass is able to spread because it is not being eaten by large livestock, and as it spreads, it creates a monoculture and kills all other plant life in its path [9]. The seeds of Barb goatgrass can easily be invade other areas by transportation on cars, people, and other animals [9]. Control measures for the grass include prescribed burns and selective mowing when the grass is still young with no seeds produced. Barb goatgrass, like most grasses, has deep, broad roots; thus, mowing is not always an effective control measure. The only effective control measure is the spraying of glyphosate, a common pesticide. The decrease in Barb goatgrass comes at the price of killing all plant life that is sprayed with glyphosate. See Barb goatgrass here.


Red-eared Slider (Trachemys scripta elegans)

Red-eared slider turtles (RES) are common pets, named for the red stripes on their head near their ears. They have entered local lentic water bodies two ways: 1) escaping captivity and 2) being released by their owners. RES typically invade large ponds and compete with the native aquatic and semi-aquatic vertebrates. The ability for RES to out-compete natives comes from its large size, making it able to claim nesting and basking spaces. RES carry Salmonella, as most reptiles do, which affects the humans who come into contact with the it and the water they reside in [10]. Native pond turtles are affected by parasites and diseases RES carry, which they have no immunity to[10]. Efforts to stop the sale of RES have been implemented since 1975, but because RES has already hybridized with native turtles, their eradication is becoming increasingly difficult. [10] A healthy RES can reach 20 years of age, making them a chronic threat to freshwater ponds. To help in the eradication of RES, report any sightings to the local Park Services or CDFW [10]. See the Red-eared Slider here.

Northern and Southern Watersnakes (Nerodia sipedon and Nerodia fasciata, respectively)

These two snakes are amphibious predators that feed on a variety of animals, including: frogs, salamanders, fish, and rodents [11][12]. Northern Watersnakes are primarily aquatic, seldom hunting outside of lentic water bodies [11], while Southern watersnakes hunt aquatic and terrestrial animals [12]. Northern Waternsnakes are mostly found in Northern California [11], while Southern Watersnakes have been found in Sacramento, Yolo, and Los Angeles counties [12]. The two snakes cause large decreases their prey populations, and are also competition for California's endangered native giant garder snake. Southern watersnakes are resistant to brackish water and like their northern counterparts, have voracious appetites [11][12]. If these snakes are spotted, their presence should be reported to the CFDW. See a Northern Watersnake and a Southern Watersnake.


Wild turkey (Meleagris gallopavo)

Wild turkeys are common across California, specifically in vegetated areas near urbanization. They were first imported in the 1600s for hunting, and again in the 1990s. Turkeys have been in California for many decades, but recently, they have become a concern for local ecosystems because of their ability to compete with native species. It is still under debate whether a turkey is an invasive species, however. Turkeys are considered charismatic birds and enjoyed by many, but because they are large birds that move as a group, they are able to eat more than the smaller native ground birds[13]. Some ecologists believe that turkeys out-compete local native birds such as the California Quail, but previous studies found this is incorrect[14][15]. Short-term experiments have shown that quail and turkey share common habitat, but quail prefer to live beside roads, where turkeys prefer to live near large trees where they roost at night [13][14] As adults, turkeys do not have many predators besides humans during the turkey hunting season, but as chicks they are prey for bobcats and other medium sized predators. Turkeys are generalists and have no preference for food; arguably eating whatever they can swallow. This, along with their increase in populations, may serve as a threat for local ground birds, but is not proven[13][14].

Turkeys are common in wooded areas [14][16] in Marina, located in the California Central Coast (specifically on Inter-Garrison Road), but avoid highly urbanized areas [16] such as the California State University Monterey Bay Campus.

Parrots and Parakeets (Family Psittacidae)

Parrots and Parakeets are seen as exotic pets by many, but they are an invasive species in California when they are released by their owner or escape. Parrots and Parakeets (Psittacids) were brought to America in the late 19th to mid 20th centuries, escaped the pet trade, and created their own small, isolated populations [17]. Psittacids play the niche-stealing role as an invasive species and will compete with native bird species that forage on seeds and fruit[18]. Native birds outnumber the Psittacids drastically, and as such, ecologists are not concerned with their presence because they are not in large enough numbers to cause food web collapse in native populations [18]. Psittacids are common in San Francisco, but are not encountered as much in central to Southern California [18].


American bullfrog (Lithobates catesbeianus)

Bullfrogs are large amphibians that will eat whatever they can fit in their mouths and out-compete their native counterparts [19]. Bullfrogs have voracious appetites, and eat rodents, bats, and other vertebrates, both terrestrial and aquatic[19]. They were first released into the Western states as a biologic control, but their numbers quickly increased [19]. These large frogs are also known to be resistant carriers of the chytrid fungus known to infect and kill many other types of amphibians such as native frogs and salamanders. Shorebirds like herons and cranes will eat bullfrogs if they are present, but the frogs emit a painful screech when trapped or harmed, which usually causes their predator to release them. Some native snake venom is ineffective against the bullfrog, making them essentially a species with no predators. Bullfrogs will tolerate cold or hot temperatures by hibernating or aestivating until the temperature suits its preferences [19]. Report any bullfrog sightings to a local wildlife agency (i.e., CDFW or State Parks). See an American Bullfrog here.


Feral Cats and Dogs (Felis catus and Canis lupus familiaris, respectively)

An overpopulation of domestic cats and dogs invariably leads to portions of these populations to become feral and homeless. Although they are domesticated animals, these mammals do not completely lose their ability to hunt and survive without the help of humans. Feral dogs are mainly found in very urban areas, where they feed on trash and discarded food, and hunt in packs for bigger prey, such as ungulates and other mammals [4]. Feral cats are more infamous for hunting local songbirds, and because they hunt so frequently, many of the songbird populations decline [20]. These hunted populations have the potential to be endangered and threatened species of birds[20]. Domesticated cats also pose a threat to the local bird populations because of their tendency to hunt for enjoyment and their large population (95 million [21]) [20]. Both feral groups are capable of attacking people when provoked or for no apparent reason[4]. Report any dangerous feral cat or dog to the local animal control service.

Nutria (Myocastor coypus)

Nutria, commonly called Coypu, are large rodents typically seen on the East coast as invasive species, but they were spotted in Merced, California in 2017 [22]. Nutria can be compared to beavers in that they are semi-aquatic and eat the vegetation in and around water. These large rodents mainly eat grasses and small shrubs that hold wetland soil together. Nutria are ecosystem engineers known to convert wetlands to open water [22]. The conversion of wetland habitat to open water not only removes organisms that rely on vegetation to survive, but also destroys habitat for future use. Wetlands are already a shrinking habitat and their conservation is necessary for biodiversity. Report Nutria sightings to the CDFW immediately, as they can cause expensive or irreparable damage [22]. See a Nutria here.


The Asian Longhorned Beetle (Anoplophora glabripennis)

The Asian Longhorned Beetle(ALB) have not been recognized as invasive species in California, but a graduate student from California State University Monterey Bay saw one in Modoc County, California in July of 2018. All states are at risk of ALB infestation.

ALB are large, black and white beetles in the family Cerambycidae which bore into and feed on a variety of hardwood trees [23]. Like all beetles, they are capable of flight, but they are mostly transported as eggs and larvae in imported firewood[23]. The life cycle of the ALB occurs in the hardwood trees that the mother bores into. When enough ALB are present in a tree, it will die and the adults find more trees to reproduce in. Adults are present year-round because larvae can overwinter, causing a staggered release of adults into the environment [23]. ALB are capable of killing entire forests if enough of them are present. [23] The ways to reduce the spread of ALB are to report their presence to local rangers, buy only locally produced firewood, and do not enter ALB quarantined areas of forests. [23] The eggs of ALB can be transferred in many ways, including firewood, lumber, and on people, resulting in their potential widespread distribution. If spotted, ALB presence should be reported to the CDFW immediately. See an Asian Longhorned Beetle here.

Argentine Ant (Linepithema humile)

The Argentine ant is a cosmopolitan invasive species, but is very common in the Central Coast of California because of the Mediterranean climate. See more on Invasive Invertebrates of the Central Coast.

Ambrosia Beetles (Curculionidae subfamilies Platypodinae and Scoltyinae)

These unique beetles in two weevil subfamilies with a symbiotic relationship with the Ambrosia fungi. The beetles and the fungi feed on the inner walls of the tree bark they infest [24][25]. These beetles mostly infest dead trees, but they have been recorded infesting stressed and healthy trees. Ambrosia beetles and their fungal symbiotic partners infest non-native trees invading native forets [24]. Ambrosia beetles have not been recorded to show any threat to native trees, and have little to no negative ecological effects. See an Ambrosia Beetle (Platypodinae) here.


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