Aquatic Invasive Species

CISR: Caulerpa taxifolia

Anonymous — Mon, 20 Jan 2020 21:30:51 +0000

CISR: Caulerpa taxifolia Anonymous (not verified) Mon, 01/20/2020 - 13:30 More Blog Posts CISR Team May 27, 2009

The Situation: Caulerpa taxifoliais an invasive alga that is causing serious environmental problems in the Mediterranean Sea. This invasive weed was discovered in southern California and New South Wales, Australia in 2000. Caulerpa taxifolia was officially eradicated from southern California in 2006.

Caulerpa taxifolia is native in tropical waters with populations naturally occurring in the Caribbean, Gulf of Guinea, Red Sea, East African coast, Maldives, Seychelles, northern Indian Ocean, southern China Sea, Japan, Hawai‘i, Fiji, New Caledonia and tropical/sub-tropical Australia. A cold water strain of this attractive tropical alga, possibly developed from plants that initially originated from Australia, was selected for by aquarium managers at the Wilhelma Zoo in Stuttgart, Germany in 1980. By 1984, this coldwater strain of Caulerpa had been released into the Mediterranean Sea by the Oceanographic Museum of Monaco where it established.

Currently, Caulerpa has colonized thousands of hectares of sea bottom in the Mediterranean and it is found from France to Croatia and its range in the Mediterranean will likely to continue to expand. The invasive strain of Caulerpa can tolerate low sea water temperatures and can survive out of water, in moist conditions, for up to 10 days. This alga can colonize most kinds of substrates including rock, sand, mud, and seagrass beds from depths ranging from less than 1 m to ~12 m.

Caluerpa is capable of rapid growth and reproduction of the invasive strain is asexual and dispersal occurs through fragmentation. Fragments as small as 1 cm give raise to viable plants. Long distance spread occurs via ballast water discharge from transoceanic boats and illegal dumping of aquaria plants. More localized dispersal occurs through the unintentional movement of plant material on boats, anchors, or fishing gear, or via algal fragments being dispersed by sea currents.

The Problem: The invasive strain of Caulerpa in the Mediterranean Sea smothers other algal species, seagrasses and sessile invertebrate communities. It does this by either out-competing species for food and light or due to the toxic effects of caulerpenyne compounds that are contained in its foliage. Large meadows of Caulerpa have vastly reduced native species diversity and fish habitat. Native fish which are able to eat Caulerpa, such as Mediterranean bream, accumulate caulerpenyne toxins in their flesh which makes these fish unsuitable for human consumption.

The appearance of Caluerpa in southern California in 2000 was most probably caused by an aquarium owner improperly dumping the contents of a marine fish tank into a storm water system that fed into Agua Hedionda Lagoon in Carlsbad where this weed was first discovered. California has since passed a law forbidding the possession, sale or transport of Caulerpa taxifolia within the state. There is also a federal law under the Noxious Weed Act forbidding interstate sale and transport of the aquarium strain Caulerpa.

When first detected the populations of Caulerpa in southern California were small enough for eradication to be feasible. To eradicate underwater populations of Caulpera, patches were covered with tarpaulins which were held down with sandbags which sealed the edges. Chlorine was poured under the sealed tarpaulins which trapped the chlorine. Chlorine in this instance acted as a pesticide and killed living organisms trapped under the tarpaulins, including Caulerpa. The unintentional killing of fish, invertebrates, and plants while not desirable was deemed necessary and preferable to letting Caulpera spread unchecked.

Economic Impact: Small infestations found in Agua Hedionda Lagoon in Carlsbad near San Diego and Huntington Beach near Los Angeles, took six years to eradicate at a cost of more than $7 million (US). So far no other infestations of the cold water strain of Caulerpahave been located in the USA. In the Mediterranean commercially important fisheries have been adversely affected because fewer fish live in areas with heavy Caulerpa infestations.

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CISR: New Zealand Mud Snail

Anonymous — Mon, 20 Jan 2020 21:28:39 +0000

CISR: New Zealand Mud Snail Anonymous (not verified) Mon, 01/20/2020 - 13:28 More Blog Posts CISR Team May 27, 2009

The Situation: As the common name indicates, this invasive pest is native to New Zealand. New Zealand mud snail has had a long invasion history. It was first found in the United Kingdom in 1859, the western Baltic in Europe in 1887, the Mediterranean and eastern Europe were invaded in the 1950’s. The snail has also established Australia and Japan. In 1987, New Zealand mud snail was found in Idaho (the Snake River). It has since spread through Yellowstone National Park, and is now found in Wyoming, Montana, and Oregon (1994). The Great Lakes were invaded in 1991. Genetic analyses suggest that the source population in the Great Lakes likely originated from Europe and invaders were introduced into the Great Lakes in ballast water discharged from transoceanic ships that came from Europe. The snail was found in British Columbia Canada in 2007, and the first record of this pest in California was from the Owens River which was officially confirmed in 2000. All western US states, except New Mexico, now have permanent populations of New Zealand mud snail.

The color of the snail shell is variable, and can range from gray and dark brown to light brown. The snail is usually 4-6 mm in length in areas that have been invaded, but snails can grow to almost twice this size, up to 12 mm, in New Zealand where populations are much lower. New Zealand mud snail is a nocturnal grazer that feeds on plant and animal detritus, algae, and diatoms. Invasive populations have an unusual mode of reproduction. New Zealand mud snails can reproduce asexually and female snails are born with developing embryos inside them. Consequently, all populations consist of genetically identical clones. In New Zealand, native mud snail populations consist of sexually reproducing populations (the males make up less than 5% of the populations) and asexually reproducing females. Each snail can produce around 230 offspring a year, and reproduction typically occurs during the spring and summer.

The Problem: New Zealand mud snail has likely been introduced into new areas by fishermen who have not properly cleaned equipment such as waders, wading boots, nets, and other gear. Because New Zealand mud snails are so small they are easily overlooked on fishing gear, and they are very resistant to desiccation. Snails can live for 24 hrs without water, and for up to 50 days on damp surfaces. This level of hardiness provides ample time for inadvertent movement of hitchhikers before they die. The snail is also tolerant of estuarine conditions and can live at depths of up to 45 m on solid and silty substrates. Once introduced into a new area, New Zealand mud snails can reach densities exceeding 500,000 per square meter. The exact implications of these incredibly high population densities are not certain. However, it is thought that such high snail populations probably have a negative affect on populations of other aquatic organisms, especially native snails and the insects and fish that feed on them. It is likely that freshwater ecosystems are adversely affected by such high populations of an invasive snail.

The highest concentration of New Zealand mud snails ever reported was in Lake Zurich, Switzerland, where the species colonized the entire lake within seven years to a density of 800,000 per square meter. Interestingly, these massive populations were not sustained, and a population crash due to unknown causes occurred. Consequently, New Zealand mud snails are not as common as they once were in Lake Zurich. A similar event was apparently observed in Denmark.

There are no known specialized natural enemies of New Zealand mud snail that have accompanied this invader as it has moved globally. Lack of predators, parasites, and pathogens has almost certainly promoted the invasion success of this pest. In New Zealand, the mud snail is attacked by 11 species of trematode, a type of parasitic flatworm, which sterilizes infected snails. This parasite may be important for regulating mud snail populations in New Zealand thereby preventing them reaching the incredible densities seen overseas. It is possible that host specific trematodes exist in New Zealand and these may be used to control pest populations of New Zealand mud snail if they can be shown to pose no risk to desirable native snail populations in areas that have been invaded by this pest.

Control of the New Zealand Mud Snail: Since there are no feasible eradication technologies, the first line of defense against New Zealand mud snail is containment. Since spread appears to be strongly associated with recreational freshwater fishing and wading gear, there are several recommended ways to reduce the risk of spreading New Zealand mud snail throughout California. Some suggested ways to decontaminate fishing gear include freezing overnight, or treating with chemicals known to be toxic to New Zealand mud snail. Many freshwater fishing websites have decontamination recipes for cleaning gear of New Zealand mud snail.

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CISR: Quagga & Zebra Mussles

Anonymous — Mon, 20 Jan 2020 21:27:58 +0000

CISR: Quagga & Zebra Mussles Anonymous (not verified) Mon, 01/20/2020 - 13:27 More Blog Posts CISR Team May 28, 2009

The Situation: Quagga and zebra mussels are aquatic invasive species that are native to eastern Europe. The quagga mussel originated from Dnieper River drainage of Ukraine. The zebra mussel was first described from the lakes of southeast Russia and its natural distribution also includes the Black and Caspian Seas. Quagga and zebra mussels get their common names from the zebra-type striping on the shells. Both mussel species are small and typically grow to the size of a fingernail. They are prolific breeders and these mussels can attach to both hard and soft surfaces in freshwater ways.

Zebra mussels have a long history of invasion and have successfully established in Great Britain (1824), The Netherlands (1827), The Czech Republic (1893), Sweden (1920), Italy (1973), the Great Lakes in the USA (1988), and California (2008). Quagga mussels were first found in the USA in the Great Lakes in 1989, Nevada in 2007, and California in 2008. Ballast water discharge from transoceanic ships is thought to be responsible for the long distance spread of zebra and quagga mussels from their original home ranges in eastern Europe. Short distance spread between fresh waterways within countries most likely occurs via the movement of recreational boats. This occurs when boats are not cleaned and dried adequately and contaminated watercraft are then moved from infested waterways to pristine water bodies where mussels are accidentally introduced. These mussels can survive for 3-5 days out of water without suffering lethal desiccation.

Where quagga and zebra mussels co-exist, quagga mussels appear to outcompete zebra mussels, and quagga mussels can colonize to depths greater than those achieved by zebra mussels and are more tolerant of colder water temperatures. For example, in Lake Michigan, zebra mussels made up 98.3% of mussels in 2000, by 2005 quagga mussels represented 97.7% of collected mussels. Zebra mussels were found at densities of around 899 per square meter, but quagga mussels now dominate at 7,790 mussels per square meter. Quagga mussels have been found at depths of up to 540 feet in Lake Michigan where they filter feed year round.Consequently, quagga mussels may end up being the more problematic of these two mussel species in California.

The Problem: Quagga and zebra mussel invasions have had catastrophic impacts in the ecosystems in which they have established. These organisms clog water intake structures (e.g., pipes and screens), which greatly increases maintenance costs for water treatment and power plants. Recreational activities on lakes and rivers are adversely affected as mussels accumulate on docks, buoys, boat hulls, anchors, and beaches can become heavily encrusted.

The shells of both mussel species are sharp and can cut people, which forces the wearing of shoes when walking along infested beaches or over rocks. Mussels adhering to boat hulls can increase drag, affect boat steering, and clog engines, all of which can lead to overheating and engine malfunctions. Ecological problems also result from mussel invasions. Zebra and quagga mussels can kill native freshwater mussels in two ways: (1) attachment to the shells of native species can kill them, and (2) these invasive species can outcompete native mussels and other filter feeding invertebrates for food. This problem has been particularly acute in some areas of the USA that have a very rich diversity of native freshwater mussel species.

The encrusting of lake and river bottoms can displace native aquatic arthropods that need soft sediments for burrowing. In the Great Lakes this had lead to the collapse of amphipod populations that fish rely on for food and the health of fish populations has been severely affected.

These mussels have been associated with avian botulism outbreaks in the Great Lakes which have caused the mortality of tens of thousands of birds. Because of their filter feeding habit, it has been estimated that these mussels can bioaccumlate organic pollutants in their tissues by as much as 300,000 times when compared to concentrations in the water in which they are living. Consequently, these pollutants can biomagnify as they are passed up the food chain when contaminated mussels are eaten by predators (e.g., fish and crayfish), who in turn are eaten by other organisms (e.g., recreational fishermen who eat contaminated fish.) High mussel populations can increase water acidity and decrease concentrations of dissolved oxygen.

Interestingly, invasions by quagga and zebra mussels have been documented as having some positive affects on receiving ecosystems. For example, filtration of water by mussels as they extract food removes particulate matter. This filtration has improved water clarity, and reduced the eutrophication of polluted lakes. In some instances these improvements may have benefited local fishing industries. Conversely, improved water clarity allows penetration of light to greater depths which can alter the species composition of aquatic plant communities and associated ecosystems. This improved water quality is thought to aid algal blooms that get washed ashore where they rot making recreational beaches unusable. Further, the highly efficient removal of phytoplankton can deprive other aquatic species of food.

Invasion success in some areas of California may be affected by water chemistry. Waterways around the Sierra Nevada mountains may have insufficient calcium (an element needed for shell growth) and some lakes in northeast California may be too salty for mussel survival. However, the general consensus is that most freshwater ways in California will be accommodating to zebra and quagga mussels.

Economic Impact and Management: Zebra and quagga mussel invasions create an immense financial burden because of the need to continuously and actively manage these pests. It has been estimated that it costs over $500 million (US) per year to manage mussels at power plants, water systems, and industrial complexes, and on boats and docks in the Great Lakes. Similar yearly management costs are anticipated for California. For example, a recent estimate (2009) by the Army Corps of Engineers indicates that quagga mussels could cause annual loses of $22 million to the Lake Tahoe region should they establish there. The report details potential damage to tourism, reduced property values, and increased maintenance costs. Management of problematic mussel populations may be achieved in different ways in California. Water draw downs in canals and aqueducts could be used to kill mussels by drying them out. Poisons such as chlorine and copper sulfate which are toxic to quagga and zebra mussels could be employed under certain conditions.

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CISR: Chytrid Fungus

Anonymous — Mon, 20 Jan 2020 21:21:57 +0000

CISR: Chytrid Fungus Anonymous (not verified) Mon, 01/20/2020 - 13:21 More Blog Posts CISR Team August 08, 2009

The Situation: Upwards of 40% of amphibian species are in decline worldwide, owing to several factors such as habitat loss, environmental degradation, pollutants, and disease. Recently the fungal pathogen Batrachochytrium dendrobatidis has emerged as a major threat to amphibians. Amphibians infected with B. dendrobatidis develop chytridiomycosis, which eventually causes death in susceptible species. The first documented outbreaks of chytrid fungus occurred in the late 1990s simultaneously in Australia and Central America. Since then the pathogen has been detected in over 100 amphibian species and has been associated with severe population declines or extinctions in several regions throughout the world. A great deal is still unknown about the biology of this pathogen, therefore it remains an active area of research for disease ecologists and conservation biologists.

Chytrid Fungus on FrogsDamage: B. dendrobatidis is an external pathogen that attaches to keratinized portions of amphibians, including the mouthparts of tadpoles and the skin of adults. The fungus reproduces via sporangia, and may be spread by movement of flagellated zoospores, direct contact between hosts, or between host stages. Growth of the fungus leads to degradation of the keratin layer, which eventually causes sloughing of skin, lethargy, weight loss, and potentially death. The physiological mechanism for chytrid-induced mortality is not known, but it appears to stem from disruption of skin function – such as fluid transport or gas exchange.

The chytrid fungus is known to infect over 100 species, but susceptibility to disease is highly life stage and species specific. For example, in mountain yellow legged frog (Rana muscosa) tadpoles suffer generally mild sublethal effects, with most mortality occurring at metamorphosis when there is a rapid production of newly keratinized skin tissue. Conversely, several other amphibian species appear to be relatively tolerant to B. dendrobatidis – including some widespread exotic or invasive species, such as the marine toad (Bufo marinus), American bullfrog (Rana catesbeiana), and African clawed frog (Xenopus laevis)).

At the population level, chytrid fungus outbreaks have been associated with local and possible species extinctions in Australia, Central America, and the United States. For example, in 2004 chytrid fungus prevalence in parts of Panama increased from 0 to nearly 60% over approximately 4 months, with concomitant declines in amphibian density and diversity of over 80% and 60%, respectively. B. dendrobatidis is thought to thrive in cool, moist habitats. This has been used to argue that cooling trends observed in parts of Central America are driving chytrid-induced amphibian extinctions in these regions.

Distribution: One explanation for the recent emergence of chytridiomycosis in amphibians, the “novel pathogen hypothesis”, is that B. dendrobatidis existed historically as a locally distributed pathogen that only recently was spread to new regions. Alternatively, the “endemic pathogen hypothesis” posits that the chytrid fungus was historically widespread but that recent environmental change (e.g., climate change, pollutants, habitat degradation) altered its pathogenicity. The relative importance of these two mechanisms is currently a source of debate. Low genetic diversity among geographically distant B. dendrobatidis strains is consistent with the first hypothesis, but synchronicity of chytrid fungus outbreaks in disparate, intact habitats supports the latter hypothesis.

The first described outbreaks of chytrid fungus occurred in 1998 in both Australia and Central America. Since then B. dendrobatidis infections have been documented throughout the Americas, including Mexico and the U.S., Europe, and most recently in Southeast Asia.

The oldest known chytrid fungus infections are from museum specimens of African clawed frogs (Xenopus laevis) collected in 1938. These specimens have been used to argue for an African origin for B. dendrobatidis. It is believed that the chytrid was then spread to other continents in the 1960s and 70s through commercial trade of these African frogs.

Research: The link between chytridiomycosis and amphibian decline is an active area of research worldwide. The genome of B. dendrobatidis has been sequenced, which should prove useful for identifying the origin, mechanisms of virulence, and potential control methods for this pathogen. University of California researchers have been studying this pathogen for several years, especially the impacts of chytrid fungus on populations of the mountain yellow legged frog (Rana muscosa) in the Sierra Nevada Mountains in California. This once abundant alpine frog has undergone severe declines in recent years, with numerous local die-offs. Research is being conducted on the spatial epidemiology of disease in R. muscosa, to understand why some local populations persist whereas others go extinct. Projects include identifying the modes of pathogen spread, impacts of outbreaks on alpine food webs, and the population genetic consequences of outbreaks for frogs. With regard to frog population and disease management, experiments include evaluating the efficacy of anti-fungal treatments and the feasibility of reintroducing frogs into previous outbreak areas.

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CISR: Didymo (or Rock Snot)

Anonymous — Mon, 20 Jan 2020 20:22:05 +0000

CISR: Didymo (or Rock Snot) Anonymous (not verified) Mon, 01/20/2020 - 12:22 More Blog Posts CISR Team October 28, 2009

The Situation: Didymo or rock snot, is a highly invasive species of freshwater diatom that can form large and extensive mats in rivers, streams, and lakes. Didymo is native to cool temperate areas of the northern Hemisphere including Europe, North America, and Asia. In 2004, didymo was discovered infesting freshwater rivers in the South Island of New Zealand, the first record of this diatom in the Southern Hemisphere. Even in parts of what is presumed to be the native range of didymo, this pest is starting to expand its range aggressively. The reasons for this change in behavior are not known.

The Problem: Because of the extensive smothering of rocks and other underwater structures, habitat and food sources can be changed or eliminated to the detriment of other organisms living in infested waterways. Excessive biomass accumulations associated with didymo result from asexual reproduction. When the diatom divides, the stalk that was attaching the diatom to a rock or some other hard surface divides also. As this process repeats itself a mass of branched interconnected stalks results. It is the aggregation of these stalks, which are highly resistant to degradation, that causes the formation of large mats of didymo, or rock snot. Outbreaks of didymo are thought to have contributed to the declines of freshwater invertebrate and vertebrate populations, especially fish that have important recreational value (e.g., trout fisheries). This relationship between didymo and fish declines is an area of active research. The recreational value of infested waterways is severely reduced because large clumps of rock snot floating down stream catch on fishing flies, spinners, and hooks demanding almost constant removal each time line is retrieved.

Didymo is almost certainly moved into new areas via contaminated fishing equipment (e.g., boots, waders, and line) and boats. Sanitation measures should be employed to reduce the spread of moving didymo from infested to uninfested areas. Such practices include removal of all obvious clumps of didymo from boats and fishing equipment. Soaking fishing gear in bleach or saltwater solutions, heating for prolonged periods, or freezing for several consecutive days can kill sterilize fishing gear by killing didymo.

Distribution: Didymo is thought to be native to some areas of North America, but historically it was rare in areas in which it was present. Currently, didymo is expanding its range in North America and its presence has been confirmed from Vermont, New Hampshire, New York, Virginia, West Virginia, Tennessee, Colorado, Arkansas, Wyoming, Utah, Idaho, Montana, Washington State, North Dakota, South Dakota, Alaska, and in Canada from British Columbia and Alberta. In California, didymo has been found in the South Fork of the American River.

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