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Effectiveness of EarthTec (R) for killing invasive quagga mussels (Dreissena rostriformis bugensis) and preventing their colonization in the Western United States

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Quagga mussels (Dreissena rostriformis bugensis) have created economic and ecological impacts in the western United States since their discovery in 2007. This study focuses on chemical control for preventing the spread of these mussels. The effectiveness of EarthTec® in killing quagga mussels (adults, juveniles, and veligers) in Lake Mead, Nevada-Arizona, was evaluated over time across six concentrations: 0, 1, 5, 10, 17, and 83 ppm. One hundred percent mortality of adult and juvenile mussels was achieved after 96 h with 17 ppm and 5 ppm (respectively), and 100% veliger mortality occurred within 30 min at 3 ppm. From December 2010 to February 2011, the effectiveness of EarthTec® in preventing veliger colonization was also evaluated and the results showed that 2.8 ppm was effective in preventing veliger colonization on fiberglass panels. This study indicates that EarthTec® has the potential to be an effective control agent against the invasive quagga mussel, and more specifically, in preventing the colonization of veligers.
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Effectiveness of EarthTec® for killing invasive
quagga mussels (Dreissena rostriformis bugensis) and
preventing their colonization in the Western United
States
Ashlie Watters a , Shawn L. Gerstenberger a & Wai Hing Wong a b
a Department of Environmental and Occupational Health, University of Nevada Las Vegas,
4505 Maryland Parkway, Las Vegas, NV, 89154-3064, USA
b Department of Biology, State University of New York at Oneonta, 108 Ravine Parkway,
Oneonta, NY, 13820, USA
To cite this article: Ashlie Watters , Shawn L. Gerstenberger & Wai Hing Wong (2013): Effectiveness of EarthTec® for killing
invasive quagga mussels (Dreissena rostriformis bugensis) and preventing their colonization in the Western United States,
Biofouling: The Journal of Bioadhesion and Biofilm Research, 29:1, 21-28
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Effectiveness of EarthTec
1
for killing invasive quagga mussels (Dreissena rostriformis bugensis)
and preventing their colonization in the Western United States
Ashlie Watters
a
, Shawn L. Gerstenberger
a
and Wai Hing Wong
a,b
*
a
Department of Environmental and Occupational Health, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas,
NV 89154-3064, USA;
b
Department of Biology, State University of New York at Oneonta, 108 Ravine Parkway, Oneonta, NY
13820, USA
(Received 16 May 2012; final version received 25 October 2012)
Quagga mussels (Dreissena rostriformis bugensis) have created economic and ecological impacts in the western
United States since their discovery in 2007. This study focuses on chemical control for preventing the spread of these
mussels. The effectiveness of EarthTec
1
in killing quagga mussels (adults, juveniles, and veligers) in Lake Mead,
Nevada-Arizona, was evaluated over time across six concentrations: 0, 1, 5, 10, 17, and 83 ppm. One hundred
percent mortality of adult and juvenile mussels was achieved after 96 h with 17 ppm and 5 ppm (respectively), and
100% veliger mortality occurred within 30 min at 3 ppm. From December 2010 to February 2011, the effectiveness
of EarthTec
1
in preventing veliger colonization was also evaluated and the results showed that 2.8 ppm was
effective in preventing veliger colonization on fiberglass panels. This study indicates that EarthTec
1
has the
potential to be an effective control agent against the invasive quagga mussel, and more specifically, in preventing the
colonization of veligers.
Keywords: Dreissena rostriformis bugensis; quagga mussel; EarthTec
1
; copper sulfate; molluscicide; chemical
control; biofouling
Introduction
The zebra (Dreissena polymorpha) and the quagga
mussel (Dreissena rostriformis bugensis) have become
arguably the most serious nonindigenous biofouling
pests introduced into North American freshwater
systems (LaBounty & Roefer 2007). The economic
impact of zebra and quagga mussels in North America
has been estimated at $1 billion a year (United States
Army Corps of Engineers 2002). The speed at which
the quagga mussel has spread throughout the south-
western United States is unprecedented (Benson 2011;
Wong & Gerstenberger 2011). In addition to invading
the Great Lakes region, the quagga mussel was
subsequently discovered in Lake Mead in 2007
(LaBounty & Roefer 2007), and following establish-
ment has resulted in significant economic impacts. For
example, the mussels clog water intake pipes and
disrupt water filtration in electric generating plants and
water treatment facilities. They also affect boat motors,
damage recreational equipment, and once established
in the lake, routine maintenance is necessary to avoid
additional impairment. The cost in the western United
States will be significant with the further spread to
uninfested bodies of water (Turner et al. 2011). Quagga
mussels also alter the ecosystem by increasing water
clarity and bioaccumulating contaminants. With their
efficient filtering capabilities, quagga mussels remove
suspended food particles from the water column,
including detritus, phytoplankton and bacterioplank-
ton, reducing availability for native filter-feeding
aquatic species (Claudi & Mackie 1994; Strayer et al.
1999; Karatayev et al. 2007; Nalepa et al. 2009).
Chemical means are the most commonly used
methodology in both the United States and Europe to
control zebra and quagga mussel macrofouling (Claudi
& Mackie 1994). Following the introduction of
nonindigenous zebra and quagga mussels to North
America, a number of chemicals with unknown and
known molluscicidal properties were proposed for use
in controlling invasive molluscs (Sprecher & Getsinger
2000). The most popular and least expensive chemical
used for control of invasive mussels is chlorine, where
it is added as chlorine gas or as liquid sodium
hypochlorite (Claudi & Mackie 1994; Rajagopal
et al. 1996; Sprecher & Getsinger 2000). Chlorine is
beneficial because it is effective at low concentrations
and efficient against all fouling categories ranging from
bacteria to molluscs. It not only kills adult quagga
mussels, but is effective in preventing embryonic forms
(ie veligers) from settling in raw water piping systems
*Corresponding author. Email: david.wong@oneonta.edu
Biofouling, 2013
Vol. 29, No. 1, 21–28, http://dx.doi.org/10.1080/08927014.2012.744825
Ó2013 Taylor & Francis
Downloaded by [State University College], [Wai Hing Wong] at 20:37 30 November 2012
which can increase the efficiency of the water facility
(Jenner & Janssen-Mommen 1993). Chlorine controls
mussels through an oxidation process either directly on
the adults or through inhibition of settlement and
growth of the veligers. Adult mussels can sense the
presence of chlorine in low doses to which they
respond by shutting their valves resulting in cessation
of filter-feeding and dependence on anaerobic meta-
bolism (Rajagopal et al. 1997, 2002). Because mussels
try to avoid the chemical, they may die from
asphyxiation or metabolic acidosis induced by anae-
robic metabolism over a prolonged period (Van
Benschoten et al. 1995). Trihalomethanes (THMs)
are formed as by-products of chlorination when it is
used to disinfect drinking water. These byproducts are
formed when chlorine reacts with organic or inorganic
material already present in the water being treated.
THMs are linked to adverse health effects and can be
carcinogenic to animals (Cotruvo & Regelski 1989).
The US Environmental Protection Agency (US EPA)
set a standard for the maximum allowable annual
average concentration level of total THMs of 80 ppb
(US EPA 2010). Water treatment facilities that use
chlorine as a preventative measure against veliger
colonization must monitor total THM production to
avoid hazardous limits. In cases where THM exceeds
the US EPA’s limit, an alternative form of chemical
control needs to be implemented.
EarthTec
1
is a proprietary copper chemical that
may be used as a chemical control method for quagga
and zebra mussels. It is formulated by blending copper
sulfate pentahydrate with Earth Science Laboratory’s
base acid. EarthTec
1
is registered with the US EPA as
an algicide/bactericide and certified as a drinking water
additive. It is commonly used in lakes, ponds,
reservoirs, and municipal drinking and wastewater
systems. The biologically active ingredient in Earth-
Tec
1
is the cupric ion form of copper (Cu
2þ
).
Quagga mussels have been threatening the local
ecosystem and environments since their introduction,
and currently there is not a single method that will
eliminate the problem. The objective of the present
study was to determine the lethal dose of EarthTec
1
for quagga mussels, and to test the effectiveness of this
agent in preventing settlement by quagga mussel
veligers. This information will be useful as an added
option for the management of quagga mussel
biofouling.
Materials and methods
Lethal effects of EarthTec
1
on quagga mussels
Specimen collection and holding conditions
In November, December, and January 2010–2011,
adult, juvenile, and veliger specimens of D. rostriformis
bugensis were collected from Lake Mead, Nevada-
Arizona, USA (3681050.690N; 114846012.950W). Adults
and juveniles were collected from rope substrata at
depths of 10–20 m, and veligers were collected at 30 m
using a 64 mm pore size plankton net (Gerstenberger
et al. 2011). A National Park Service permit was
obtained, granting permission to collect quagga
mussels. Immediately following collection, the samples
were brought back to the Nevada Department of
Wildlife’s (NDOW) hatchery in Boulder City, NV to
acclimate for 5 days, in 10 gallon (¼37.9 1) tanks. The
aquaria used to acclimate adult and juvenile mussels
contained water taken from a flow through system
carrying water pumped directly from Lake Mead. The
water in the aquaria was continuously aerated with air
stones and the temperature was recorded daily. Adults
(411 mm) and juveniles (511 mm) were divided and
placed into twenty four, 800 mm fine media mesh bags
with 12–15 mussels per bag. Veligers were divided into
small, glass Petri dishes for the toxicity experiment, or
divided into the 10 gallon tanks for the colonization
experiment. Twelve tanks equipped with air stones
were used and filled with 25 l of raw Lake Mead water.
Adult, juvenile, and veliger toxicity tests
Six concentrations of EarthTec
1
solution were tested
for the adult, juvenile, and veliger toxicity: 0 (control),
1, 5, 10, 17, and 83 ppm with corresponding Cu
2þ
concentrations of 0 (control), 0.06, 0.3, 0.6, 1, and
5 ppm, respectively. Only healthy mussels in the fine
media mesh bags were used for experimentation. The
duration of both the adult and juvenile portions of
the toxicity tests was 7 days (168 h). Four replicates of
the six treatment groups (including controls) were used
for the toxicity tests. In total, for each adult and
juvenile test, 240 mussels of roughly equal size
(*11 mm 723 mm) were used for the toxicity experi-
ments (10 mussels 66 treatment groups 64 repli-
cates ¼240 total mussels). Each replicate was placed
in a 800 mm mesh bag and immersed in a beaker with
raw Lake Mead water and the appropriate dose of
EarthTec
1
. Each beaker was aerated with an air stone
and kept in a 228C water bath to mimic the epilimnion
water temperature of Lake Mead. Each group was fed
daily with 0.1 ml of Instant Algae
1
Isochrysis 1800
(Reed Mariculture, Campbell, CA) at a concentration
of 1 610
6
cells ml
71
.
For the veliger toxicity portion of the experiment,
the Ecological Effects Test Guidelines for bivalve acute
toxicity test was followed (US EPA 1996). Unlike the
adult and juvenile tests, this portion of the experiment
did not exceed 48 h (US EPA 1996). Quagga mussel
veligers (n¼10–20) were pipetted into small, glass
Petri dishes and examined under a stereo microscope
22 A. Watters et al.
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(Olympus Stereo Zoom, model SZ4045ESD) to assess
viability. Both dead and living veligers were counted
and documented for each Petri dish.
Adult, juvenile, and veliger mortality
Mortality was checked every 24 h from the beginning
of the experiment for adults, and at 6 h and 12 h
followed by every 24 h for the juveniles. To test for
mortality, gaping mussels were first gently prodded on
their shell valves with forceps; those individual mussels
that did not respond by immediate shell closure were
stimulated in the area of their siphons. Mussels that still
did not respond to siphon stimulation, had their shell
valves forcibly closed with forceps. The mussel was
considered dead if it immediately reopened upon
release of the forceps (Harrington et al. 1997; Morse
2009; Comeau et al. 2011). Dead mussels were removed
from the beaker, their shell length recorded to the
nearest 0.1 mm with digital calipers (Model 62379-531:
VWR International, Inc) followed by placement into a
different mesh bag. They were then transferred to a flow
through system and mortality was confirmed 24 h later.
The experiments for both adult and juvenile mussels
lasted 7 days (168 h). The shell lengths of mussels that
were still alive at 168 h were similarly recorded.
Determination of mortality using cross-polarized
light (CPL) microscopy immediately followed the
addition of EarthTec
1
to each Petri dish containing
viable veligers. When veligers stopped moving or
internal organs appeared to cease movement under a
microscope for a 2-min observation period, they were
documented as dead (Britton & Dingman 2011). If
100% mortality was not observed within 3 h, the Petri
dish was set aside and examined every 12 h thereafter,
until 36 h was reached. Prior to each treatment, the
control groups were examined to evaluate viability.
The effectiveness of EarthTec
1
for preventing veliger
colonization
The colonization experiment was performed in two
phases on veligers that were collected as described
previously. Both phases lasted 30 days, with six
controls (0 ppm) and six treatments of 1 ppm
(0.06 ppm of Cu
2þ
) of EarthTec
1
in Phase I. Phase
II consisted of four controls, four treatment groups of
2 ppm (0.12 ppm of Cu
2þ
), and four treatment groups
of 3 ppm (0.18 ppm of Cu
2þ
). Fiberglass panels
(79 66861.66 mm) were hung in each tank with
fishing line from the shelf above. Five days before the
experiment, the fiberglass panels soaked in fresh Lake
Mead water to form a biofilm. The panels were used to
measure colonization of veligers. The veligers were fed
twice daily with 0.375 ml of Instant Algae
1
Isochrysis
1800 (Reed Mariculture, Campbell, California)
(1.54 610
8
cells). Every week, half the water in the
tanks was exchanged and replaced with fresh Lake
Mead water. To prevent the loss of the veligers, the
water being removed was filtered in the cone portion of
the plankton net with 64 mm pore size and the veligers
were placed back into the corresponding tank. Each
tank received a minimum of 25 veligers l
71
of water.
After veligers were added to an aquarium, the
appropriate amount of Earth Tec
1
was added to the
medium to attain the appropriate test concentration.
Because EarthTec
1
is considered a low pH product,
the pH of the water in all tanks was analyzed (YSI
EcoSense pH100), and the average pH in the treatment
tanks was 8.25 (range ¼8.24–8.26).
Panel analysis
After 30 days, the fibreglass panels were removed from
all tanks and were brought back to UNLV’s Environ-
mental and Occupational Health Laboratory. CPL
microscopy was used to assess the colonization status
of attached quagga mussel juveniles. Each mussel was
then photographed with the Zeiss Discovery V8 stereo
microscope (Carl Zeiss, Inc., Peabody, MA). To mea-
sure the amount of colonization, all six surfaces of the
panel were observed. To determine the number of
mussels per m
2
, the total number of colonized juveniles
was divided by 0.01.
Statistics and data interpretation
Analysis of covariance (ANCOVA) was used to
examine the effectiveness of different doses of Earth-
Tec
1
on killing mussels at different time intervals (Zar
1996). Analysis of variance (ANOVA) was used to
evaluate if there was any significant difference in
minutes to reach 100% veliger mortality among
different treatment groups in the veliger toxicity test.
Student-Newman-Keuls post hoc multiple comparisons
test was conducted to determine if the difference was
significant. For the colonization experiment, t-test and
ANOVA were used to determine if there was
significant difference among treatments in Phase I
and Phase II, respectively. Linear regression was
performed to estimate the concentration of EarthTec
1
at which a zero colonization rate was reached. The
significance criterion was set at a¼0.05. All statistical
analyses above were performed using SAS
1
Software
(version 9.2, SAS Institute Inc. Cary, NC).
Results
The concentration of EarthTec
1
significantly affected
the survival of adult mussels with time as a significant
Biofouling 23
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covariant (p50.0001). Higher concentrations of and
increased exposure times to Earth Tec
1
resulted in
greater levels of mussel mortality. No mortality
occurred in control groups of adult mussels. The
time to 100% mortality of adult quagga mussels
decreased with increasing EarthTec
1
concentration
(Figure 1A). Similar results were found among juvenile
mussels (Figure 1B): higher concentrations of Earth
Tec
1
and/or increased time of exposure led to higher
levels of mortality (ANCOVA, p50.0001).
In the adult and juvenile toxicity tests, the control
groups and the 1 ppm of EarthTec
1
groups showed no
or little mortality. In the adult toxicity test, 50% of the
mussels in the 83 ppm group of EarthTec
1
were dead
by 30 h. By 96 h, 450% of the mussels in the group
with 5 ppm were dead, 450% of the mussels in the
group with 10 ppm were dead, and all the mussels in
the 17 and 83 ppm groups were also dead. By 168 h,
95% of the mussels in the 5 ppm group were dead and
92.5% in the 10 ppm group were also dead (Figure
1A).
In the juvenile toxicity test, 98% of the mussels in
the 5 ppm group were dead by 72 h, and 3% were dead
in the 1 ppm group. Mortality was confirmed by 96 h
for all the mussels except the controls and the 1 ppm
group (Figure 1B).
Based on the acute toxicity of EarthTec
1
to
adult and juvenile quagga mussels, their 96 h LC
50
values were estimated to be 3.42 ppm and 1.40 ppm,
respectively.
Veliger toxicity
Doses of 3, 5, 10, 17, and 83 ppm of EarthTec
1
were
effective for killing 100% of the veligerswithin
minutes. Mortality occurred in 510 min for mussels
treated with 83, 17, and 10 ppm. For mussels treated
with 5 ppm and 3 ppm, mortality occurred in 530
and 20 min, respectively (Table 1). The experiment was
completed after 36 h, and all the controls and
individuals in the groups with 1 ppm were still alive.
The time required for 100% mortality to occur varied
significantly between treatments (ANOVA, p50.001;
F
6,23
¼372,022). As anticipated, Student-Newman-
Keuls multiple comparisons showed that the time to
100% mortality was significantly longer when treated
with 3 ppm and 5 ppm than with higher doses such as
10 ppm, 17 ppm, and 83 ppm (Table 1).
Colonization experiment
For data obtained in Phase I of the colonization
experiment, a pooled t-test was performed. The groups
with 1 ppm of EarthTec
1
had a lower colonization
rate compared to the control group (p50.01) (Figure
2A). In Phase II of the colonization experiment, the
treatments with 3 ppm of EarthTec
1
had a zero
colonization rate (Figure 2B). The groups treated
with 2 ppm and 3 ppm were less colonized than the
control group (ANOVA, p50.01) (Figure 2B) while
there was no significant difference between 2 ppm and
3 ppm (p40.05).
Assuming the control (0 ppm) treatment had a
100% colonization rate in Phase I, an average 32%
colonization rate was found for 1 ppm. The same
assumption was applied for the Phase II experiment
where the colonization rates for 0 ppm, 2 ppm, and
Table 1. Time for quagga mussel veligers to reach 100%
mortality at different doses of EarthTec
1
.
EarthTec
1
Minutes (Mean +SD) Replicates
0 ppm Mortality was 0 8
1 ppm Mortality was 0 6
3 ppm 27.5 +7.5 4
5 ppm 20.3 +8.1 3
10 ppm 6.0 +2.0 3
17 ppm 6.0 +1.0 3
83 ppm 5.7 +4.5 3
Figure 1. Cumulative mortality of quagga mussel adults
(A) and juveniles (B) at different EarthTec
1
concentrations.
n¼240, mean +1 SD.
24 A. Watters et al.
Downloaded by [State University College], [Wai Hing Wong] at 20:37 30 November 2012
3 ppm treatments were 100%, 7%, and 0%, respec-
tively. Therefore, EarthTec
1
with 1 ppm, 2 ppm, and
3 ppm had reduced colonization rates of 68%, 93%,
and 100%, respectively. Because both control treat-
ments had a 100% colonization rate, least square fit
regression was used to determine the relationship
between colonization rate (%) and dose (ppm).
Because of zero values in both dependent variable
(colonization rate) and independent variable (dose), an
exponential curve is not developed. Therefore, the
colonization data were log(y þ1) transformed and
this also addresses the heteroscedasticity of limited
data (Zuur et al. 2007). A linear regression was pro-
duced to elucidate the dose-response relationship
(Figure 3). The following relationship was found:
Log (Colonization Rate% þ1) ¼70.70 6Dose þ
2.00 (R ¼0.98, p50.01). Therefore, to result in zero
colonization, it is estimated that 2.8 ppm (95%
confidence level: 1.0–3.0 ppm) of EarthTec
1
is
necessary for winter months (December to February).
The corresponding Cu
2þ
concentration is 0.17 ppm
(95% confidence level: 0.06–0.18 ppm).
Discussion
The first portion of the study showed that EarthTec
1
was lethal to quagga mussels. Higher concentrations of
EarthTec
1
and longer exposures were required for
100% mortality in adult mussels compared to juveniles
or veligers. To kill 450% of the mussels by 96 h, at
least 5 ppm of EarthTec
1
(0.30 ppm Cu
2þ
) was
needed. For 100% mortality of adult mussels, 5 ppm
was administered over 168 h. Depending on the
location and the current amount of copper already in
the water source, 5 ppm (0.3 ppm of Cu
2þ
) of Earth-
Tec
1
may be too high to use in a facility that treats
drinking water. Therefore, control methods may be
better targeted towards veligers compared to adult or
juvenile mussels.
The results of this study suggest that EarthTec
1
is
more effective for killing adult and juvenile quagga
mussels than another algicide/bactericide/cyanobacter-
icide, Cutrine
1
-Ultra. Cutrine
1
-Ultra is a chelated
copper formulation that is effective in penetrating thick
cell walled algae and vascular aquatic plants (Applied
Biochemists 2002). When adult zebra mussels (D.
polymorpha) were exposed to 1,214 mgCul
71
(1.2 ppm Cu) for 48 h, 50% mortality was achieved
(Kennedy et al. 2006). This amount of copper is below
the US EPA’s maximum containment level (MCL) of
1.3 ppm. After continuous exposure for 96 h, it took
almost two times the maximum allowable dosage of
Cutrine
1
-Ultra to kill most of the adult zebra mussels.
Another study examined the toxic effects of copper
sulfate (CuSO
4
) on adult zebra mussels, and found
them to be resistant to copper, resulting in a 48 h LC
50
of 5.3 ppm Cu l
71
, but the LC
50
fell to 2.5 ppm Cu l
71
after continued assessment of survival (Waller et al.
1993).
In the juvenile toxicity segment of the present
study, most of the mussels were dead by 48 h when
5 ppm of EarthTec
1
was used. These results are
similar to those found in the adult toxicity segment.
However, time was reduced by 50%. It took 72 h for
100% mortality for juvenile mussels exposed to 5 ppm
of EarthTec
1
(Cu
2þ
0.3 ppm). Waller et al. (1993)
found the LC
50
for juvenile zebra mussels (shell length
Figure 2. Colonization density of quagga mussels treated
with 0 and 1 ppm (A) and 0, 2, and 3 ppm (B) of EarthTec
1
.
Mean +1 SD; values shown on top of the bars are means.
Figure 3. Relationship between the percentage colonization
rates and EarthTec
1
dose in quagga mussel colonization.
Mean +1 SD. Note that the data on y-axis are log (y þ1)
transformed.
Biofouling 25
Downloaded by [State University College], [Wai Hing Wong] at 20:37 30 November 2012
5–8 mm), after continuous exposure for 48 h to
be 42 ppm of CuSO
4
. This amount exceeds the
MCL set by the US EPA at 1.3 ppm of copper.
EarthTec
1
was found to be toxic to quagga mussel
veligers, presumably because at this early life-stage
they do not have a thick protective shell and
membrane function is less well developed, therefore
making them more susceptible to copper ions. In the
present study, 2.8 ppm of EarthTec
1
(0.16 ppm Cu
2þ
)
was found to be effective for killing quagga mussel
veligers in minutes. Based on personal observation,
EarthTec
1
was effective on all life stages of veligers,
from trochophores to pediveligers. Kennedy et al.
(2006) found the highest 24 h LC
50
value for the early
life stages (trochophores) of veligers to Cutrine
1
-Ultra
was 13 mgCul
71
(0.013 ppm Cu). The study showed
that this chemical is effective for killing the earliest life
stage, trochophores. However, it did not investigate its
toxicity to later, more developed veliger stages.
The second segment of the study examined the
effects of EarthTec
1
on preventing quagga mussel
veligers from colonizing fiberglass substrata. In Phase I
and Phase II, EarthTec
1
was effective in preventing
veliger colonization. Phase I of the colonization
experiment showed that a greater density of mussel
colonization occurred in the control groups whereas
there was far less colonization in the 1 ppm group
(p50.01). Mussel colonization was successfully
deterred when veligers were exposed to 1 ppm of
EarthTec
1
(0.06 Cu
2þ
). Phase II of the colonization
study was conducted in January, where water tem-
peratures were lower (range ¼9.68C–13.38C) com-
pared to Phase I where water temperatures were
warmer (range ¼12.38C–13.38C). It was found that
there was very little colonization in the 2 ppm groups
compared to the control groups, while no colonization
occurred in the 3 ppm groups. The data are in
agreement with the previous experiment that showed
3 ppm was lethal to quagga mussel veligers (Table 1).
The 3 ppm experimental value is also very close to the
statistically predicted value of 2.8 ppm (Figure 3).
Therefore, it is recommended that 2.8 ppm of Earth-
tec
1
can prevent quagga mussel colonization.
Presently, chlorine is the most commonly used
chemical for prevention of veliger mussel colonization.
One study that was conducted in a field laboratory
found that an intermittent 2 h daily treatment with 1
mg l
71
chlorine reduced mussel settlement by 91%
compared with the controls. Although, chlorine is
effective in preventing quagga mussel veligers from
settling, densities of up to 6000 m
2
still occurred
compared to the control settlement monitors which
reached 147,100 m
2
(Bidwell et al. 1999). The same
study also looked at using half the amount of chlorine
(0.5 mg l
71
) for 4 h day
71
, and similar reductions in
mussel colonization were found. The 2 to 4 h chlorine
treatments did cause a reduction in settling, but the
breaks in treatment were sufficient for the veligers to
feed and grow (Bidwell et al. 1999). The intermittent
chlorine schedule in this study may work for a short
time; however, it will not prevent 100% of mussels
from fouling.
Recommendations for further study
Chemical management strategies targeting early larval
stages of quagga mussels are more likely to be cost
efficient and less prone to non-target environmental
impact than strategies aimed at controlling adults and
juveniles. The toxicity experiment was conducted from
late November to early February when the veligers are
competent in colonization in Lake Mead (Gerstenber-
ger et al. 2011). Therefore, a lower dose, such as
1 ppm, may still be effective in preventing colonization
in other seasons when veligers were less competent.
Since veliger dynamics in Lake Mead vary by season,
further studies on the impacts of different seasonal
temperature regimes on the effectiveness of Earth Tec
1
in preventing quagga mussel settlement may be
required to determine the lowest effective dose required
to prevent any mussel settlement or fouling.
EarthTec
1
may be most effective in the summer
time when water temperatures are higher. Copper
toxicity increases with an increase in temperature and
decreases at lower temperatures. Rao and Khan (2000)
examined the toxicity of CuCl
2
on zebra mussels (D.
polymorpha) with increasing water temperatures. The
ambient water temperature was set at 158C, and then
tested at 208and 258C. A 48 h LC
50
of 0.78 ppm CuCl
2
at 208C decreased to 0.24 ppm CuCl
2
at 258C. A
similar effect occurred during a 96 h exposure to
CuCl
2
. The 208C 96 h LC50 of 0.5 ppm CuCl
2
declined to 0.11 ppm at 258C. Because summer surface
water temperatures in Lake Mead approach 28–308C,
the concentration of Earth Tec
1
required to prevent
mussel fouling may be greatly reduced during warm
summer months. Thus, the concentrations of Earth
Tec
1
required to prevent mussel fouling may have to
be reevaluated relative to temperature conditions
during the application period.
More research needs to be done in Lake Mead to
understand better the lethality of EarthTec
1
to the
various larval development stages so the appropriate
lethal dose to prevent pediveliger settlement can be
determined. Research also needs to examine the lethal
doses to different stages of veligers in different seasons
when environmental factors, such as temperature and
food quantity and quality are a challenge. It has been
documented that quagga mussel veligers are present
year-round in Lake Mead, with the percentage of
26 A. Watters et al.
Downloaded by [State University College], [Wai Hing Wong] at 20:37 30 November 2012
settlement competent veligers peaking at 460% dur-
ing the fall and declining to 55% in February when
surface water temperatures are at their lowest (Ger-
stenberger et al. 2011). The veliger abundance in Lake
Mead was found to be strongly associated with the
water temperature in the metalimnion (Gerstenberger
et al. 2011). Therefore, experiments need to be
designed to examine different chemical doses to
prevent settlement over a wide range of seasonal
temperatures at which settlement occurs. In that case,
chemical control may be implemented in low doses
and/or for a reduced amount of time when the water
temperature is low in winter time. This would reduce
the amount of chemical that is necessary for applica-
tion; hence, reducing cost and the adverse impact on
the surrounding ecosystem. The significantly higher
chemical sensitivity of veligers compared to adult and
juvenile mussels has pertinent implications in the
design and use of the chemical. Application of
chemical controls in the environment is dependent on
a two major factors. Firstly, the chemical needs to be
effective against the target organism (ie quagga
mussels) and secondly it must not have adverse effects
on non-target species in the environment. Further-
more, chemical control plans need to be safe, practical,
easy to implement, and cost effective. Therefore,
because of the elevated toxicity of Earth Tec
1
to
quagga mussel larval stages relative to juveniles and
adults and its capacity to prevent mussel settlement at
relatively low application doses, prevention of mussel
settlement and fouling may be the most cost-effective
and environmentally acceptable Earth Tec
1
applica-
tion technology.
Apart from chemical control, there are other
alternative treatment methods in quagga/zebra mussel
control and management, such as physical and
mechanical cleaning, freezing, desiccation, and biolo-
gical control. Among these alternative methods,
thermal control is an optimistic and more environmen-
tally benign method to control mussel fouling that has
been tested and adopted by many water treatment
plants and power industry (Perepelizin & Boltvskoy
2011; Grutters et al. 2012 and references therein), as
well as agencies that decontaminate boats to prevent
the overland dispersal of invasive mussels (Morse 2009;
Comeau et al. 2011).
Conclusions
For the toxicity portion of the study, 5 ppm of
EarthTec
1
(Cu
2þ
0.3 ppm) killed 100% of quagga
mussel adults by 168 h and juveniles by 72 h, while for
veligers, 3 ppm was effective in 530 min. For the
colonization portion of the study, 1 ppm of EarthTec
1
(Cu
2þ
0.06 ppm) reduced veliger colonization on
fiberglass panels. However, the present study was
conducted in a laboratory setting, and it cannot be
assumed that the same results would occur if con-
ducted in the field because of uncontrolled conditions.
While chemical control of quagga mussels has been
proven effective in laboratory studies and closed
systems, the recommended higher doses required for
adult and juvenile eradication restricts the use of harsh,
chemical-based strategies in field studies. The best way
to combat this issue with chemical control, is to
determine the most sensitive life stage and tailor
management techniques to that specific life stage, and
in this case, the veliger. This would optimize target
efficacy while minimizing chemical release into the
environment, risk to non-target species, and cost that
would be required.
Acknowledgments
This study was supported by National Park Service and
Earth Science Laboratories, Inc. This study would not have
been completed without the help and support from the staff
at the Nevada Department of Wildlife’s Fish Hatchery, along
with the many people who reviewed this manuscript.
Constructive comments from three anonymous reviewers
were helpful in improving the quality of a previous version of
this manuscript.
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28 A. Watters et al.
Downloaded by [State University College], [Wai Hing Wong] at 20:37 30 November 2012
... EarthTec QZ.-EarthTec QZ, a USEPA-registered, copper-based molluscicide, is also used to control dreissenid mussels. In laboratory studies, EarthTec QZ applied at 1 mg/L reduced the colonization of quagga mussel veligers on fiberglass panels (Watters et al. 2013). Additionally, quagga mussel veligers were more sensitive to the chemical than were juvenile or adult life stages (Watters et al. 2013). ...
... In laboratory studies, EarthTec QZ applied at 1 mg/L reduced the colonization of quagga mussel veligers on fiberglass panels (Watters et al. 2013). Additionally, quagga mussel veligers were more sensitive to the chemical than were juvenile or adult life stages (Watters et al. 2013). Exposure of zebra mussel adults to EarthTec QZ at 1 mg/L for 72 h resulted in 100% mortality (Claudi et al. 2014), and the exposure of juvenile quagga mussels to 5 mg/L for 72 h resulted in 98% mortality (Watters et al. 2013). ...
... Additionally, quagga mussel veligers were more sensitive to the chemical than were juvenile or adult life stages (Watters et al. 2013). Exposure of zebra mussel adults to EarthTec QZ at 1 mg/L for 72 h resulted in 100% mortality (Claudi et al. 2014), and the exposure of juvenile quagga mussels to 5 mg/L for 72 h resulted in 98% mortality (Watters et al. 2013). ...
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Wildland firefighting equipment moves large volumes of raw water during fire incidents in order to extinguish flames or control fire growth. This water movement may serve as pathways for aquatic invasive organisms to be moved between water bodies and watersheds. The equipment used may become contaminated and serve as vectors for future invasions across large geographic areas. New guidelines used by federal firefighting agencies recommend the application of sanitation solutions using quaternary ammonium compounds for decontaminating wildland fire equipment to prevent the spread of aquatic invasive species that may foul the equipment. While quaternary ammonium compounds have been tested on other aquatic organisms, the effectiveness of such compounds has not been systematically tested on dreissenid mussels. We tested the survival of quagga mussel veligers after exposure to a 3% solution of Sparquat 256® for 5 and 10 minutes. We assessed survival immediately after treatment and then after 60 minutes in fresh water. We found that a 5 minute exposure duration was insufficient to kill 100% of tested veligers. However a 10 minute exposure, as prescribed in the interagency operational guidelines for preventing spread of aquatic invasive species, was effective in killing all tested veligers, but not immediately after treatment. An additional 60 minutes were required after the quaternary ammonium solution was removed before 100% mortality was achieved. This work highlights the need for more rigorous evaluation of the effectiveness of various sanitation solutions in killing quagga and zebra mussels under different ambient temperatures in order to validate and refine the sanitation protocol for firefighting equipment and other applications.
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Increase in water temperature from an ambient of 15 degrees C to 20 and 25 degrees C increased the respiration rate in zebra mussels, Dreissena polymorpha, by 50 and 175%, respectively, and increased the toxicity of copper; a 48-hour lethal concentration to kill 50% of the organisms (LC50) of 775 mu g/L at 20 degrees C decreased to 238 mu g/L at 25 degrees C, and a 96-hour LC50 of 487 mu g/L at 20 degrees C reduced to 107 mu g/L at 25 degrees C. The oxygen consumption rate in the presence of 150 mu g/L copper decreased by 16% at 20 degrees C and by 50% at 25 degrees C. Thus, high temperatures may increase the toxicity of copper, and possibly other metals, to zebra mussels. Similar increases in heavy metal toxicity may also accompany global warming, which is expected to raise surface water temperature by 2 to 3 degrees C. Such temperature and heavy metal combinations may also be useful in designing field trials to control this nuisance species.
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Introduction.- Data management and software.- Advice for teachers.- Exploration.- Linear regression.- Generalised linear modelling.- Additive and generalised additive modelling.- Introduction to mixed modelling.- Univariate tree models.- Measures of association.- Ordination--first encounter.- Principal component analysis and redundancy analysis.- Correspondence analysis and canonical correspondence analysis.- Introduction to discriminant analysis.- Principal coordinate analysis and non-metric multidimensional scaling.- Time series analysis--Introduction.- Common trends and sudden changes.- Analysis and modelling lattice data.- Spatially continuous data analysis and modelling.- Univariate methods to analyse abundance of decapod larvae.- Analysing presence and absence data for flatfish distribution in the Tagus estuary, Portugual.- Crop pollination by honeybees in an Argentinean pampas system using additive mixed modelling.- Investigating the effects of rice farming on aquatic birds with mixed modelling.- Classification trees and radar detection of birds for North Sea wind farms.- Fish stock identification through neural network analysis of parasite fauna.- Monitoring for change: using generalised least squares, nonmetric multidimensional scaling, and the Mantel test on western Montana grasslands.- Univariate and multivariate analysis applied on a Dutch sandy beach community.- Multivariate analyses of South-American zoobenthic species--spoilt for choice.- Principal component analysis applied to harbour porpoise fatty acid data.- Multivariate analysis of morphometric turtle data--size and shape.- Redundancy analysis and additive modelling applied on savanna tree data.- Canonical correspondence analysis of lowland pasture vegetation in the humid tropics of Mexico.- Estimating common trends in Portuguese fisheries landings.- Common trends in demersal communities on the Newfoundland-Labrador Shelf.- Sea level change and salt marshes in the Wadden Sea: a time series analysis.- Time series analysis of Hawaiian waterbirds.- Spatial modelling of forest community features in the Volzhsko-Kamsky reserve.