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Green Tunnels of Invasive Weeds
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December 16, 2013
The rich green foliage and delicate flowers of water hyacinth (Eichhornia crassipes) may appear ornate and decorative in backyard ponds, but the vigorous growth of this South American native plant has caused severe economic and recreational impacts, and also threatens local biodiversity, on all continents except Antarctica. Water hyacinth clogs waterways and irrigation canals, reduces oxygen levels in surface waters, and crowds out native species. Its dense mats reduce light penetration, which lowers photosynthesis and productivity at the base of the food chain and subsequently reduces food sources for native fish species. Immensely expensive to control (hyacinth management in China alone was estimated to cost more than $1 billion annually), the species has earned the dubious honor of inclusion among the world's worst invasive alien species, as compiled by the International Union for Conservation of Nature, and designation as a "weed of national significance" (applied by the Australian government to 20 noxious species of extreme invasiveness based on their potential for spread and economic and environmental impacts).
Dense mats of this free-floating plant, which are able to double in size in less than two weeks under favorable conditions, have become a familiar -- and worrisome -- sight in some areas of California's Central Valley. This is particularly true in the Sacramento-San Joaquin Delta, where water hyacinth was introduced near the beginning of the 20th century. In fact, the species has become so abundant that the California Division of Boating and Waterways considers it too well established for eradication, and herbicides are used to control the abundance of water hyacinth when no undue risks to special-status species or subsequent human water uses are anticipated.
Physical removal is perhaps the most effective method for short-term control of water hyacinth in small bodies of water, yet the high cost of mechanical removal limits its application in most infested waterways. Control of the species' abundance through harvest for practical uses is limited, and though water hyacinth meets the criteria for bioenergy production (as a perennial, abundant, bio-degradable, and high-cellulose plant), technical and logistical challenges imposed by the plant's high water content prevent commercial-scale harvesting for methane production (Ndimele et al. 2011). In recent years, biological control measures involving Amazonian weevils, moths, and fungal pathogens have been implemented in various locations to successfully reduce the abundance of hyacinth to levels that are no longer problematic, while other bold (and perhaps less than realistic) ideas of releasing pig-sized, semi-aquatic South American rodents with a penchant for consuming water hyacinth remain to be tested.
 While both Chinook salmon and water hyacinth are widely distributed, the Central Valley may be the only place where these two species collide. The presence of hyacinth can alter the composition of native plant and animal communities, and associated changes in invertebrate abundance affect the food base available to rearing fishes in the Delta (e.g. Toft et al. 2003). However, the effects of hyacinth on salmon are unknown, likely due to the relative rarity of such interactions. How returning Chinook salmon may react to "green tunnels" created by the free floating plant, which was observed stretching from bank to bank on the lower Tuolumne River earlier this fall (pictured above), remains to be investigated.
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Recent Blog Posts
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Metal and water don't mix
 Monitoring fish populations requires the use of many different types of specialized equipment. One of the most prevalent devices used for monitoring salmon has been the trusty rotary screw trap (RST). First designed and used in the late 1980s by the Oregon Department of Fish and Wildlife, RSTs have been used in the San Joaquin Basin to enumerate the outmigration of juvenile salmonids since the early 1990s. While the basic RST design has stayed the same (a rotating cone positioned in the river current to guide fish into a livebox), FISHBIO has continued to modify it to improve the practicality of using RSTs in a variety of locations for extended periods of time. Many of the RSTs that we use at FISHBIO spend 10 months of the year in the rivers we monitor, exposed to the extremes of cold winters and blistering summers. But the river itself adds another environmental factor: when metal is submerged in water, it becomes susceptible to rust or corrosion. Our Fablab has tried a variety of different materials to improve the durability of the RSTs, but each material has its drawbacks. Currently, the cone portion of the trap is made of a stainless steel mesh, while the livebox and the pontoons that float the trap are made of aluminum. The durability of aluminum allows a product to withstand the elements for extended periods of time and its light... Read more >
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IN THE NEWS: Recent stories you might have missed...
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EU discards ban will change the way we fish our seas
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How plastic in the ocean is contaminating your seafood
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We've long known that the fish we eat are exposed to toxic chemicals in the rivers, bays and oceans they inhabit. The substance that's gotten the most attention - because it has shown up at disturbingly high levels in some fish - is mercury. But mercury is just one of a slew of synthetic and organic pollutants that fish can ingest and absorb into their tissue. Sometimes it's because we're dumping chemicals right into the ocean... Read more >
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