The Quagga and Zebra
Mussel Problem
The Quagga and Zebra mussels, Dreissena
rostriformis bugensis and Dreissena polymorphaare respectively, are two species
of freshwater bivalve mollusks that are non-native and a major concern to the
United States. The two species of mussels have costs the U.S. billions of
dollars in recovery, prevention, and damage due to the nature of these two
mussels. While each mussel has its own distinct properties and characteristics
that make them unique, the similar disturbance these mussels cause ecologically
and economically have caused the two mussels to be grouped together when
discussed in public forums (Ciborowski, 2012).
The Quagga Mussel
The Quagga mussel is indigenous to
the Denieper River drainage of the Ukraine. Like the Zebra mussel, it has
stripes and/or zig zags but these stripes fade away towards the ventral side of
its shell. The mussel also can have a large range of shell morphologies but
almost always grows no bigger than 20 millimeters or about the size of a human’s
thumb nail. The Quagga mussel does not tolerate as warm of waters or desiccation
lengths as the Zebra mussels. While its range is much more limited than the Zebra
mussel, it frequently dominates lakes where both species are introduced due to
the levels of depth it can establish and the densities of mussels it can
tolerate. The Quagga mussel has a life span of 3 – 5 years. They are prolific
breeders which mean the organisms can produce hundreds of progeny at a time (100th
Meridian Initiative, 2011).
The Zebra Mussel
The Zebra mussel is originally
native to the streams of southern Russia but as of recent has become invasive
to many different countries worldwide. The zebra mussel also has an average
size of a fingernail but can grow up to a maximum length of nearly two inches. But
typically range between 0.25 and 1.5 inches. The Zebra mussels while they also
can vary in shapes almost always have a D-shaped shell. Hybridization is
possible between the two but does not occur often. The Zebra mussel has a life span of 4 – 5 years.
The Zebra mussel can produce 1,000 eggs each reproductive cycle and upwards of
about 1 million per year. The larvae are free swimming until they can find a hard
substrate to attach on and begin growth (100th Meridian Initiative, 2011).
Success, Ecology, and
Rapid Spread
The successful spread of the two
mussels has been due to their physical and reproductive characteristics. The
mussels can attach to solid substrates by means of byssus. A byssus is a group
of strong filaments that some molluscs can secrete in order to stabilize themselves.
Almost always, the mussels are found in clusters to themselves making it much
harder to physically attempt to remove the mussels.
The
mussels also spread via the free-swimming larval stages. In this stage, mussel
larvae can be transferred through water undetected. It is speculated that the
majority of the first infestations began with the ballast waters carried on
commercial ships. Ballast water is water that is taken up by the ship in order
to stabilize the vessel through travel when lacking heavy loads. When reaching
their destinations, ballast water is released as the ships become restocked
with new loads and it is here where larvae can disperse and begin to attach
themselves in their new environments (Hoddle, 2011).
The
mussels are filter feeding organisms and can process up to a gallon of water
per day. Filter feeding organisms remove particles from the water column and
use whichever particles they choose as food while dispensing of wastes on the
water body’s floors. Typically, phytoplankton and organic sediment from the
water are what is removed. Particles that are not chosen to be digested become
infused with mucus that is called pseudofeces. This process alters the nutrient
cycling of the aquatic ecosystem. Where once particles were contained in the pelagic
zones, these nutrients are heavily processed and converted down into the
benthic zones. Often in lakes, these species remove so many particles in the
lake that the depth of clarity is drastically changed. As in Lake Erie, water
clarity increased from 6 inches to up to 3 feet. Because of the differences in
clarity, many toxic and harmful bacteria can grow in depths that were
previously unachievable. High levels of bacteria often lead to large amounts of
decay that end up on shores and ruin water quality (Benson,
Richerson, Maynard, Larson, & Fusaro, 2013).
The
mussels also compete with native species of molluscs in the water bodies. Since
these non-native species do not have established predators that graze on them
in any of these areas, the invasive species overrun and outnumber the native
species that are typically found in the area. The byssus, as being able to
attach to almost any hard substrate, often attaches to the shells of native
mussels to the point where these mussels cannot open anymore (figure 2). This
can result in reduced performance and usually death. Within Lake St. Clair,
where once there were 20 known species, now molluscs samples have only found 5
species within 4 years of the lakes infestation. As in St. Clair, many areas
around the world have seen devastating impacts with the invasion of these
mussels. As numbers of these mussels become exponential, many of the algae and
suspended sediments that other species (including fish) would normally consume become
scarce and reduce the amount of food available for these other species. This
can have direct effects on the number of viable species that the lake can
support. Additionally, these mussels have a tendency to reject specific kinds
of algae, like Microcystis, which at
high levels are toxic to freshwater bodies. When all algae except one or two
are removed from a water body, these algae form blooms and will dominate.
Toxins that are released from the mussel and then stored in the benthic zones
are then consumed by other organisms and move up the food chain. (Ciborowski, 2012)
Figure 1. Overgrowth of invasive mussels on a native mussel.
A Disaster to Water
Resources
One of the most detrimental
problems of the mussels is that they invade freshwater sources. Since these
mussels thrive in environments that are not saline, they threaten the very same
water that we use for drinking and recreation. Water and ecosystems that are
poisoned either by biomagnification, bioaccumulation, sediment deposits, species
removal, and algal blooms are a threat to fishing and water toxicity (Benson,
Richerson, Maynard, Larson, & Fusaro, 2013). Additionally, as
these organisms reach exponential numbers they begin to spread into places that
can cause serious damage. Boats, docks, water pumps, and shore surfaces become
covered with these minuscule molluscs (Figures 2 & 2.5). Shores that are covered with
these mussels require individuals to wear shoes constantly because shells of
these species of mussels are sharp and rupture skin.
Figure 2. Propel damage from mussels.
Zebra
and Quagga mussels can easily attach to any surface and quickly. When boats are
submerged in the water, small groups of these mussels often in the larvae
stage, attach to the propels and hulls of boats. Stationary boats can
accumulate mussels within the engine’s crevices. When this occurs, engines can
burn out or become dysfunctional as the mussels prevent components of the boats
from working properly. Often, a boater may not notice or even observe any
mussels on any parts of the boat until the mussels begin to increase in size
and accumulate. Removal of mussels once they become clustered can be costly and
time consuming. Docks and boats that have been or are infested with the mussels
require constant maintenance as the mussels tear away the paint and surface of
the material (100th Meridian Initiative, 2011).
Figure 2.5. Shoreline spread of invasive mussels.
Since
almost all of the places where these mussels invade are areas where counties
extract most of their drinking water, many of these areas are locations of
billion dollar pumping facilities that carry out water to most of the residents
in their jurisdictions. When mussels cause pumping facilities to malfunction,
water transport can be temporarily stopped and can cost thousands to millions
of dollars to repair. Often, mussel accumulation goes without notice since
pipes cannot be observed inside and the problem augments as mussels duplicate
(Figure3). Zebra and Quagga mussels can cost water agencies millions of dollars
to control and maintain in water treatment and pumping facilities. Since these
species multiply in vast numbers, the only way to prevent a catastrophe from happening is by prevention. In 2010, at Parker Dam/Lake Havasu Arizona the density of mussels was reported at 35,000 per square meter. When these mussels
invade a new water body, often the outcome of these species getting into every
possible area of hard substrate is unavoidable. As of now, it is estimated that
it costs over 500$ million dollars per year to manage mussels at power plants,
water systems, industrial area, and on boats in the Great Lakes. It is
estimated by the Army Corps of Engineers that in the future, California will
face similar costs. If the mussel were to establish in Lake Tahoe, estimations
predict a 22$ million dollar loss taking into consideration aspects of tourism,
reduced property values, and increased maintenance. The total costs nationwide
as of now since the 1980’s for prevention and control efforts is currently at
5$ billion and increasing (Hoddle, 2011).
Figure 3. Water pipe infested with Quagga mussels.
Current Distributions
and Locations
The first of the two mussels, the
Zebra mussel, was discovered in Lake St. Clair in 1988. It is expected that the
mussel went unnoticed for two years before even being detected. The Quagga mussel was first discovered in the
Erie Canal in 1989 but was not recognized as a distinct species from the Zebra
mussel until 1991. A timeline of the mussels is provided:
As of January 2007, Zebra mussels
have been classified as inhabiting all of the Great Lakes and in 225 inland
lakes in Michigan. The mussels were thought to have first expanded by means of
commercial barges but as invasion has spread, recreational boaters are now
thought to be the primary means of invasion. Since mussels can survive out of
water without desiccation for 3-5 days, boaters who constantly frequent various
water bodies easily spread mussels across country. Where infestation was mainly
limited to the east coast in the 90s, as of now Zebra mussels have now infested
waters of Arizona in 2007 and California in 2008. Lake Mead was the first water
body in the west coast that was reported to have been infested with the Quagga
mussels. Later invasions occurred in the Colorado River, ultimately resulting
in all tributaries that are fed or connected by the Colorado River to become
infested with Quagga mussels. This includes Lake Mohave and Havasu, and the
aqueduct system which serves Southern California. The August following these
invasions then found the mussels in Lake Dixon and San Vicente Reservoir in San
Diego County (100th Meridian Initiative, 2011).
While all invasions in the past for
California were concentrated on the Southern water bodies with the Quagga
mussel, as of recent the Zebra mussels have made their way up North to San
Justo Reservoir, located an hour south from San Jose. As most of California’s
freshwater comes from the Northern water bodies and especially the Delta, the
spread of the mussel to Northern freshwater sources can have dangerously
drastic effects on California’s water supplies. San Justo as of now has been
closed entirely of recreational use and is solely open for the purposes of
research. With San Justo’s ominous tale, the rest of the California reservoirs
and lakes are in high guard for boats that are possibly exposed to the mussel.
Efforts made by programs like the Lake Berryessa Water Partnership, funded by
Solano, Yolo, and Napa county are making efforts to inspect boats rigorously
and informing the public of the potential horror that could reach the lake.
With education and boat inspections, North California water agencies are hoping
to stay clear from having the mussel invade their water bodies and water
resources; but only time will tell if prevention is enough to keep the mobile
successful mussels from being able to spread to other parts of the state.
Management Strategies
As of now the best way to prevent
the catastrophe of the Zebra/Quagga mussel is prevention. Since there is no
direct way of removing or impacting the mussel that is viable in accordance
with ecosystem health, the best way to deal with an invasion is to prevent it.
As mentioned earlier, the importance of this factor has led to programs and
coalitions amongst counties and even states like the “100th Meridian”
efforts. Educating the public on how their recreational activities can affect
the ecosystem and local water resource health can prevent the disaster of
another reservoir or lake becoming infested. Boaters are currently being
informed on the importance of draining their boats of standing water and
completely drying all compartments. A list of lakes are also shown around water
bodies of areas that are known to have been infected so as to prevent
individuals from deciding to frequent those lakes or enter another pristine
lake after recently spending time in an infested lake. The rule of thumb is to
keep your boat out and dry for at least 5 days in the summer and for at least
30 days in the cooler months. Boaters who frequent many different bodies of
water must be informed of their risky actions. One of the only ways to safely
clean a boat that has been in infested waters is by heated spray. Water in
temperatures of at least 140 degrees Fahrenheit must be used to kill any
potential hitchhikers that could have latched onto their watercraft (100th
Meridian Initiative, 2011). For the future, research
on how to remove and reintroduce native species that can gradually take over
the invasive mussel’s roles will be needed and highly beneficial for restoring
the ecology of infested water bodies.
Bibliography
100th Meridian Initiative. (2011). Quagga/Zebra
Mussels. Retrieved from 100th Meridian: 100thmeridian.org
Benson, A., Richerson, M., Maynard, E., Larson, J.,
& Fusaro, A. (2013). Nonindigenous Aquatic Species Database.
Retrieved from USGS.
Ciborowski, J. (2012). Indicatior: Invasion of Zebra
Mussels and Quagga Mussels. Environmental Protection Agency, 205:211.
Hoddle, M. S. (2011, October 13). Center for
Invasive Species research. Retrieved from University of California
Riverside.
