Proposal: Tahoe Research Supported by SNPLMA Round 10
I. Title Page
Title: Natural and human limitations to Asian clam distribution and recolonization— factors that impact the management and control in Lake Tahoe
Proposal subtheme 2b: Special status species and communities and priority invasive species
Principal
Investigator and
Receiving
Institution
Co-Principal
Investigator
Dr. Marion Wittmann
UC Davis Tahoe Environmental Research Center
291 Country Club Drive, Incline Village, NV 89451
Phone: 775-881-7560, FAX: 775-832-1673
Email: mwittmann@ucdavis.edu
•
Dr. Sudeep Chandra
Department of Natural Resources and Environmental Science
University of Nevada Reno
Agency
Collaborator
1000 Valley Road/ MS 186, Reno, NV 89512
Phone: 775-784-6221, FAX: 775-784-4530
Email: sudeep@cabnr.unr.edu
•
Dr. John Reuter
UC Davis Tahoe Environmental Research Center, Davis, CA 95617
Phone: 530-304-1473, FAX: 530 754 9364
Email: jereuter@ucdavis.edu
•
Dr. Geoff Schladow
UC Davis Tahoe Environmental Research Center, Davis, CA 95617
Phone: 530-752-3942, FAX: 775-832-1673
Email: gschladow@ucdavis.edu
•
Ted Thayer
Tahoe Regional Planning Agency
PO Box 5310, Stateline, NV 89449
Phone: (775) 588-5301, Fax: (775) 588-4527 tthayer@trpa.org
•
Steve Chilton
US Fish and Wildlife Service
Nevada Fish and Wildlife Office, P.O. Box 5310, Stateline, NV 89449
Phone: (775) 589-5265, Fax: (775) 588-4527 steve_chilton@fws.gov
•
Dave Roberts
Tahoe Resource Conservation District
870 Emerald Bay Road, South Lake Tahoe, CA 96150
Phone: (530) 543 -1501, Fax: (530) 543-1660 droberts@tahoercd.org
•
Dan Sussman
Lahontan Regional Water Quality Control Board
2501 Lake Tahoe Blvd., South Lake Tahoe, CA 96150
Phone: 530.542.5466, Fax: 530.544.2271
DSussman@waterboards.ca.gov
•
Elizabeth Harrison
Nevada Division of State Lands
901 S Stewart Street, Suite 5003, Carson City, NV 89701
Phone: (775) 684-2736, Fax: 684-2721
Grants Contact
Person eharrison@lands.nv.gov
George Malyj
UC Davis John Muir Institute of the Environment (JMIE)
Watershed Sci Bldg, RM 1105G, Davis, CA 95616
Phone: 530 752 3938, FAX: 530 754 9364 gjmalyj@ucdavis.edu
Funding requested: $249,887
Total cost share: $ 0
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Proposal: Tahoe Research Supported by SNPLMA Round 10
II. Proposal Narrative a. Project abstract The invasive bivalve, Asian clam ( Corbicula fluminea ) is established and spreading in Lake Tahoe. In 2002, low density populations (2-20 individuals per m
2
) were observed in the south eastern portion of the lake, and in 2009 densities up to 5000 individuals per m
2
have been measured.
Through extensive field collection and laboratory experimentation, the UC Davis (UCD) – UN Reno
(UNR) science team has found that this expanding population has already had significant ecological impacts on native benthic invertebrate biodiversity, has promoted filamentous algal blooms and is changing water chemistry as well as aesthetic value of the Lake Tahoe nearshore through shell deposition.
In rapid response to this nearshore invasion, federal and state agencies collaborated with UCD and UNR to develop a short term Asian clam management plan and implement a series of studies to understand the distribution, life history and reproductive strategies of this species in relation to population control.
Additionally, a series of non-chemical management strategies have been tested in small scale pilot projects in Lake Tahoe. Findings from this research have shown that Asian clam is distributed mostly in south eastern portion of the lake, with some low density satellite populations in Glenbrook Bay, Camp
Richardson and Emerald Bay. Asian clam are located at depths greater than 70 m, which is deeper than the scientific literature has described or studied. The contribution of these deepwater clam populations to nearshore populations, as well as the growth, life history or reproductive strategies of this species in a temperature limited environment is unknown. Asian clam is an environmentally tolerant species, and there are few management strategies available. The UCD-UNR research team has found that by laying rubber bottom barriers over clam beds, it is possible to reduce dissolved oxygen concentrations to 0 mg/L and that after an approximate 1-2 month period, there is 100% mortality of clams under this barrier. There is potential for population reduction of this species in Lake Tahoe using this method, but it is important to consider the feasibility of implementation given economic costs, and more importantly, the recolonization rate of Asian clam--given propagule pressure from advective transport of juveniles via water currents, and diffusive spread of adjacent populations (including the recently observed deep water beds). Recent empirical studies have demonstrated the potential for increased mortality (such as that caused by invasive species removal harvest) to lead to overcompensation (increased population growth) in invasive populations, including well known aquatic invasive species such as Asian clam, zebra mussel and river snails (Zipkin et al. 2009). The understanding of the interaction between the ecology and management of an invasive species is key toward a successful control program. The major objectives of this proposal are to (1) understand the life history (including reproduction and growth) of deepwater clam populations and their relationship with associated benthic macroinvertebrate communities, chlorophyll concentrations, temperature, water currents and nearshore clam populations as a potential source or sink of recruits, (2) develop the relationship between treatment site selection (i.e., low population density site versus high density population center site) and rate of Asian clam recolonization, and (3) perform a cost efficiency analysis of rubber bottom barrier application that is dependent on recolonization rate and site selection. b. Justification statement:
Asian clam ( Corbicula fluminea ) is the first molluscan aquatic invasive species (AIS) to have established in Lake Tahoe. Where populations are dense, Asian clam dominates native benthic macroinvertebrates, impacts water quality through concentrated nutrient excretion and associated algal blooms, and alters water chemistry as well as the aesthetic values of nearshore regions through shell deposition. Fortunately,
Asian clam is in the early invasion stage (Figure 1), i.e., it has not fully dispersed to all available suitable habitat in Lake Tahoe. A biological invasion in its early stages allows for the study of dispersal mechanisms, impacts to native communities and also provides an opportunity for the control and management of a species before it has completely invaded an ecosystem.
In collaboration with federal and state agencies and organizations (TRPA, TRCD, USFWS,
USACE, CDFG, USDA-ARS, CA State Parks, LRWQCB, NDEP, NDOW, NDSL, TWSA) and funding from sources including SNPLMA science and capital funds, CTC, USACE, USBR, LRWQCB Clean up and Abatement, and NDSL license plate funds our researchers from UC Davis (UCD) and UN Reno
(UNR) have spent the last 18 months intensively researching the lakewide distribution, life history, and
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Proposal: Tahoe Research Supported by SNPLMA Round 10 impacts to water quality and native ecosystems of Asian clam
1
. As part of this effort our research team has also experimented with non-chemical control strategies specific to the Lake Tahoe environment
(using small-scale test lots 10-20 m
2
). These investigations have led to two key observations. First, by applying benthic barriers (45 mil rubber sheets placed upon clam beds), it is possible to reduce dissolved oxygen concentrations within the sediment column to levels fatal to Asian clam. The second key observation relates to Asian clam distribution in Lake Tahoe: populations have generally continuous yet patchy distribution along the southeastern portion of the lake with smaller satellite populations occurring in discrete locations both horizontally--Emerald Bay, Camp Richardson, Glenbrook, and vertically--at greater water depths than previously observed (>70 m).
These findings have implications for the management of Asian clam and the ecology of native species impacted by Asian clams. First, they demonstrate that it is possible to kill Asian clams in Lake
Tahoe. However, the observed spatial distribution leads to the question: Will recolonization of treated areas rapidly negate the benefits of treatment? Such recolonization may come from a variety of mechanisms including advective transport of both juveniles and adults by lake currents (McMahon 1999,
Williams and McMahon 1986), “diffusive spread” of clams from areas of high concentration to adjacent areas of low concentration, the contribution of deepwater clam beds to shallow water populations (and vice versa) or some combination of all three mechanisms. None of these mechanisms have been studied or quantified in Lake Tahoe and this remains the outstanding informational gap to know whether effective control is possible, and if so, how much it would cost. The results will also inform two other important questions: (1) whether control strategy should focus on the highest density populations or the satellite populations, and 2) whether these deepwater clams may be impacting endemic species of concern—two species of blind amphipod ( Stygobromus tahoensis, Stygobromus laciocolus ), the stonefly ( Capnia lacustra ) as well as deepwater macrophyte beds that are known to provide habitat for these and other native species.
The need for a science based strategy for the prevention of further spread and the control of existing populations is clear and timely. The understanding of deep water clam populations and the recolonization rates for treatment areas in different regions of the lake are imperative for the conservation of Lake Tahoe’s native species and the pursuit of an effective AIS management program. The proposed research is intended to advance the scientific literature of invasion ecology and to guide existing management pursuits at Lake Tahoe and other locations. c. Concise background and problem statement
The Asian clam invasion is continuing to impact the nearshore region of Lake Tahoe, but not without the potential for population reduction and control. Since the 2008 discovery of dense Asian clam beds in the south eastern portion of the lake, a collaborative science team from UCD and UNR in conjunction with a number of basin agencies has created a plan for the research and development of Asian clam control in
Lake Tahoe (Wittmann et al. 2008). The Asian clam research and management plan includes the use of pilot project testing and re-testing to determine the efficacy of suction removal and benthic barriers, observation and monitoring, and the results from concurrent field and lab research to develop an informed long-term management strategy for Asian clam in Lake Tahoe. The research team has engaged in an intensive research program to study the distribution, life history, growth and reproductive strategies, impacts to algal growth and water quality, as well as field implementation of experimental non-chemical management strategies. Results of some of these research efforts are outlined below.
Asian clam biology, ecology and distribution
Through benthic grab sampling and the lakewide deployment of an autonomous underwater vehicle
1
Lake Tahoe Basin resource agency executives, elected officials ranging from county supervisors to U.S. Senators from both California and Nevada and others have publically supported the need for the science-based management of Asian clams.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
(AUV) called Gavia
2
(capable of taking high resolution imagery of the lake bottom) the UCD-UNR research team have demonstrated that Asian clam are mostly distributed in the southeastern portion of
Lake Tahoe (populations variably distributed from Cave Rock to the East Channel of the Tahoe Keys).
Newly discovered satellite populations in the southern portion of Glenbrook Bay, Camp Richardson and at the mouth of Emerald Bay (Figure 2) showed very low density (1-10 individuals/m
2
) compared to
Marla Bay (average 3000 individuals/m
2
). Asian clam are located in water depths ranging from 2 to 80 meter in regions of the Lake (Figure 3)—much deeper than the previously observed maximum depth (40 m). McMahon (1999) cites that Asian clam is restricted to shallow, nearshore lentic systems, however, there have been deepwater (80-100 m) occurrences of Asian clam observed in Lake Mead (Peck et al.
1987, Wittmann, Chandra et al. 2009), and now in Lake Tahoe. Currently there are no published findings of Asian clam growth, reproduction or life history strategies in deep waters.
Where Asian clam occurs in Lake Tahoe, it dominates the benthic macroinvertebrate community
(Figure 4), including native pea clams ( Pisidium spp.) and gastropod species ( Physella sp.
and
Planorbidae). In Lake Tahoe, an individual Asian clam is capable of filtering over 15-20 liters of lake water (and feeding on phytoplankton) in a 24 hour period. Laboratory experiments by UCD and UNR have shown that the subsequent excretion of nitrogen and phosphorus from this feeding stimulates the growth of recently observed filamentous algal species Zygnema sp . and Cladophora glomerata . These algal species have impacted the Lake Tahoe nearshore water clarity, ecology as well as human recreational use
3
. Additionally, these filamentous algal species are known in other systems to be associated with invasive bivalves (Davies and Hecky 2005), and increased levels of E. coli and other bacteria (Byappanahalli et al. 2003).
Asian clam populations in Lake Tahoe have two major reproductive events per year, with each individual capable of producing at least 150 juveniles per event. This reproductive pattern is similar to
Asian clam populations in other systems where food availability and temperature conditions are met
(Sousa et al. 2008). Lake Tahoe clam populations are increasing in numbers—maximum densities in 2008 were recorded by UCD--UNR at 3200 individuals/m
2
; in 2009 densities as high as 5000 individuals/m
2 were observed in Marla Bay. Lake current modeling to understand the movement of pelagic Asian clam veligers, as funded by SNPLMA Round 9 science grant is currently underway. Through these laboratory, modeling and field studies, it is clear that Lake Tahoe is an adequate environment for the proliferation of
Asian clam, its environmental impacts, and given recreational boater and surface current movement, has the potential to spread to many locations.
Asian clam management experimentation
Asian clam are a successful invasive species due in part to their ability to survive in a wide range of temperature, turbidity, pollutant, water flow and food availability conditions (McMahon and Bogan
2001). This tolerance to adverse conditions makes Asian clam and other invasive bivalve species difficult to control with chemical or thermal application (Mattice et al. 1987, McMahon and Lutey 1988).
However, both zebra mussels ( Dreissena polymorpha ) (Mikheev 1964, Mackie et al. 1989) and Asian clam (McMahon 1983) have been reported to be intolerant of acute hypoxia and are generally absent from chronically hypoxic waters (McMahon 2001). Exposing Asian clam to anoxia in a laboratory setting has yielded mean survival times of 11.8 and 35.1 days at 25°C and 15°C, respectively, and without mortality for 84 days at 5°C (Matthews and McMahon 1999).
Two non-chemical management techniques have been experimented on Asian clam beds in Lake
Tahoe. The use of diver assisted suction removal and various bottom barriers (inverted chambers, and plastic, polyethylene and rubber tarping) have been implemented on a small scale (3m by 3m plots) and monitored for the reduction of dissolved oxygen concentration under barriers, mortality of clams and other benthic invertebrates, and recolonization. The various phases of this management experiment began
2
The AUV was deployed in partnership with researchers from the Civil and Environmental engineering department
3 from the University of British Columbia. For more information on the AUV see: http://gavia.is/
“Marla Bay algae invasion is a mystery” August 5, 2008. Tahoe Daily Tribune. Author: Adam Jensen
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Proposal: Tahoe Research Supported by SNPLMA Round 10 in March 2009 and are currently underway. We have found that diver assisted suction removal is costly, effective at reducing (but not eradicating) Asian clam and other benthic macroinvertebrates, and is susceptible to recolonization from neighboring plots and clams remaining that were missed in the suction process. Laying a rubber barrier over clam beds reduced dissolved oxygen to 0 mg/L in 36 hours under summer temperature conditions (16-18°C) and remained at this level until removal (Figure 5). After a 1 month period of 0 mg/L dissolved oxygen, there is 100% Asian clam mortality under the rubber barrier down to the 19 cm range over which clams have been observed in the sediment column (Figure 6).
Through these pilot experiments we have observed that Asian clam removal can have variable costs, can reduce populations, and that these areas are susceptible to recolonization. Of the methods presented here, rubber bottom barriers have the greatest potential as a successful non-chemical and economically feasible control strategy for Asian clam, but also can have adverse affects if control is incomplete control, thus potentially stimulating increased Asian clam population growth (Zipkin et al. 2009). Rubber bottom barriers also impact non-target benthic invertebrates (greater than 95% reduction in native species abundance at the conclusion of this experiment), water chemistry i.e., increased sediment phosphorus release as a result of anoxic conditions, and the potential promotion of increased algal growth, associated bacteria ( E.coli
) (Byappanahalli et al.2003) or presence of other AIS such as crayfish.
Problem statement
Under the directive of the Lake Tahoe Asian clam research and management plan, the research and management team are tasked with developing an implementation strategy for control. The efficient control of Asian clam populations in Lake Tahoe depends on the associated deployment costs of treatments, and also the rate of recolonization after treatment. The UCD-UNR research team has a fundamental understanding of the basic life history strategies, distribution and potential non-chemical control strategy for Asian clam in the shallow regions of Lake Tahoe. This latter information is based on pilot studies at the 3 m by 3 m scale. The problem now is to understand the mechanisms and quantify the rate of recolonization at scales closer to those required for practical management purposes. There are approximately 100 hectares of infestation in Marla Bay—we suggest that a better understanding of recolonization at scales greater than 10 m
2
is needed prior to costly, large scale management actions. The scales to be used here are on the order of 1 acre (approx. 4000 m
2
). The precise mechanism of recolonization will also provide information on the control strategy – whether to initially focus on high concentration areas or satellite populations to control range increase. An additional complication is the recent discover of deep water clam populations and studies on their behavior fecundation and contribution to shallow water areas are urgently required and scientifically novel. The impact by these populations to endemic macroinvertebrate and plant species is likely, given that Asian clam dominated macroinvertebrates in shallow zones (Figure 4). d. Goals, objectives, and hypotheses to be tested
The primary goal is to evaluate the practical feasibility, the ecological impacts, and the economic costs of large-scale deployment of benthic barrier to control Asian clam at Lake Tahoe. This will be through the study of the natural environmental limitations of Asian clam in Lake Tahoe as well as the humanmediated limitations to Asian clam in Lake Tahoe (i.e., control strategies), and subsequent recolonization.
The hypotheses to be tested are: 1) Are deepwater Asian clams a reproducing population, and if so, are there transport mechanisms that will deliver juveniles to shallow water regions? 2) Is recolonization dominated by advective transport at the acre scale? 3) Does the rate of recolonization after treatment with rubber barriers depend on barrier size and density of surrounding populations? and 4) Given the costs associated with control, and recolonization rates measured in different plot areas, is Asian clam treatment feasible over a 5-10 year period?
Specific objectives are to:
1. Understand the life history (including reproduction and growth) of deepwater clam populations and their relationship with associated benthic macroinvertebrate communities, chlorophyll
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Proposal: Tahoe Research Supported by SNPLMA Round 10 concentrations, temperature, water currents and nearshore clam populations as a potential source or sink of recruits
2. Develop the relationship between treatment site selection (i.e., low population density site versus high density population center site) and rate of Asian clam recolonization
3. Perform a cost efficiency analysis of rubber bottom barrier application that is dependent on recolonization rate and site selection e. Approach, methodology and location of the research
The approach, method and location for each objective are presented below.
Objective 1: Deepwater clam population study: Growth, reproduction and communication with shallow water populations
We propose to study deepwater Asian clam life strategies to better understand the possible links between shallow and deep water clams at Nevada Beach where we have sensed potentially high density Asian clam populations (Figure 3). To characterize the benthic macroinvertebrate populations in these areas, benthic grab surveys using a PONAR along transects that range from 5 to 80 meter depth will be carried out twice in one year to account for population growth and the contribution of the reproductive season.
Three grab samples will be taken per depth to account for patchiness. Samples will be processed for macroinvertebrate identification, abundance, biomass and Asian clam abundance and size class distribution. Additional Asian clam samples will be removed from various depths along this transect to be dissected and processed for reproductive evidence (presence of gametes and/or pediveligers).
A growth experiment using cages that contain measured clams will be deployed at three depths at the Nevada Beach site: 10 m, 40m and 80m, to understand the differential growth rates by depth and temperature distribution (these cages have been successfully used in Lake Tahoe – Wittmann et al. unpublished). We will mark each individual clam, and measure its growth (greatest shell length anterior to posterior edges) four times over a one year period. We will characterize the habitat for clams at 10, 40 and 80 m depth by collecting temperature, water nutrient concentration, chlorophyll a and phaeophytin levels, and sediment particle size distribution and type. To further understand whether deepwater Asian clams are reproducing, we will conduct a drifting juveniles study (Cataldo and Boltovskoy 1999, Nanbu et al. 2007) with vertical plankton tows with 65 micron mesh, bi-monthly from June through October
(reproductive period). We will collect vertical tows at regular increments from the bottom (i.e., 0-20 m,
21-40 m, 41-60m, 61-80m) to understand the abundance of veligers or gametes with depth. We will place an ADCP (Acoustic Doppler current profiler) at Nevada Beach at an intermediate depth (20m > ADCP depth > 80m) for a period of 3 months. The water velocity and flow direction will inform us of water current movement (upwelling, downwelling) in this area, and potential for water current dispersal of
Asian clam veligers or adults between the deep and shallow waters of this region.
Because the application of control strategies is logistically not likely for deepwater locations in
Lake Tahoe, understanding the source-sink dynamics between the nearshore and deepwater clam beds is imperative for the pursuit of control. Source sink dynamics are central to invasion ecology (Krkosek and
Lewis 2009) for their influence on population dynamics (Brown and Kodric-Brown 1977; Pulliam 1988), species ranges (Holt 2003). Source–sink dynamics can maintain populations in poor habitats (Pulliam
1988) and reduce them in suitable habitats. In addition, few studies have linked the communication between nearshore and deepwater benthic ecology in freshwater systems. This study will contribute to both the biological invasion and limnological bodies of literature, as well as to inform the feasibility of management in Lake Tahoe.
Objective 2: Measuring recolonization in a large scale rubber treatment in high density and low density clam areas . Biological invasions can be divided into distinct population processes: arrival (the process by which individuals are transported to a new habitat); establishment (the process by which populations grow to levels that extirpation is no longer is likely); and spread (the expansion of a population’s range) (Dobson and May 1986, Shigesada and Kawasaki 1995). Corresponding to each of these invasion phases is a management activity: 1) strategies for preventing arrival, 2) detection and eradication in preventing establishment, and 3) domestic quarantines and barrier zones are strategies for
6

Proposal: Tahoe Research Supported by SNPLMA Round 10 limiting the spread of established populations (Liebhold et al. 2007). Because Asian clam has arrived and is established in Lake Tahoe, determining strategies for management activity 3 is the concern for management pursuits in this lake.
The Lake Tahoe Asian clam working group--through the utilization of LRWQCB clean up and abatement, SNPLMA capital and NDSL license plate funds--has agreed to move forward with Asian clam control experimentation using rubber barriers and has identified the need for an implementation strategy above small scale pilot plot treatments. The management of many well known invasive species in the U.S. has taken a number of different approaches—ranging from targeting the source populations, the satellite populations or some combination of both to effectively and efficiently utilize resources. We propose to use SNPLMA capital funds for 2010 will be used to acquire materials necessary for a 1 acre (>4000 m
2
) treatment in a low density Asian clam area (site outside of Lakeside Marina where average density is 800 individuals/m
2
) and for a 1 acre treatment in a high density Asian clam population center (Marla Bay, where average density is 3000 individuals/m
2
). We propose to use SNPLMA research funds to study the ecological impacts of this rubber barrier application and the population dynamics of Asian clam recolonization following such a treatment. We will carry out a pre-application characterization of benthic macroinvertebrate communities at the two sites by benthic grab sampler (PONAR) as well as SCUBAbased sampling for sediment porewater nutrient content and sediment algal content (seston). Specifically we will collect 45 PONAR samples in and around each 1 acre treatment area to identify the abundance and biodiversity of the benthic macroinvertebrate communities in these areas, and to characterize the
Asian clam populations (and thus propagule pressure) bordering these areas. The PONAR sample locations will be in regular distances from the “edge” of the barrier plot to the center, as well as along the fringe of the plot. This will aid in the differentiation of recolonization from diffusive processes of neighboring areas (i.e., clams moving from immediate regions) or from advective transport of planktonic pediveligers. The rubber barriers will remain in place for a period of 2-4 months, at which point, materials will be removed and the same sampling scheme for the pre-application characterization will occur to identify changes to the benthic macroinvertebrate community and sediment nutrient condition as a result of rubber application. For a period of 1.5 years, PONAR grab sampling will be carried out in these plots every 8-10 weeks in order to observe Asian clam and other macroinvertebrate recolonization. These 1 acre plots are located at the same sites as the pilot project experimentation, where we have previously been able to study Asian clam and invertebrate populations, recolonization, sediment type, and site logistic feasibility at a small scale. Placing the large scale rubber treatment in the same location allows for the comparison of recolonization rates between the original 3m by 3m plots and the proposed 1 acre plots.
Objective 3: Economic efficiency analysis of rubber barrier treatment given recolonization rate
Using materials and labor costs for rubber barrier treatment, the rate of recolonization of Asian clam posttreatment, and the number of times that a treatment on a given area to maintain desired levels of Asian clam density, we will perform a cost effectiveness analysis of the application of rubber barriers in a lower density population site compared to the high density population site, for a given time period. Asian clam population densities in Lake Tahoe range from 0 to 5000 individuals per m
2
. Given variable amounts of funding ($0 to millions), there is an associated population density reduction that can be achieved over time. As an example, given a theoretical $1 million control budget, and Asian clam recolonization rates for a particular management/control area (i.e., 1 acre), it would be possible to treat a low density population once per 10 year period or a high density population center site once per 5 year period to keep population densities below a desired 10 clams/m
2
. This information can be directly used to guide management pursuits in both the selection of target sites and the frequency of treatments over time. The data collected from carrying out objectives 1 and 2 will provide the information necessary to carry out this cost effectiveness analysis of objective 3.
f. Relationship of the research to previous and current relevant research, monitoring, and/or environmental improvement efforts
In 2008, members of the Lake Tahoe Aquatic Invasive Species Working Group (LTAISWG) and UCD-
UNR science team began to develop a strategy to control the existing Asian clam beds in Lake Tahoe. In
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Proposal: Tahoe Research Supported by SNPLMA Round 10
2009, field and laboratory research were successfully carried out with results that inform both scientists and lake managers on the extent of the Asian clam invasion as well as the demonstration of potential nonchemical tools for the treatment of populations. This has been a rapidly evolving discussion built upon agreements that pilot investigations will be conducted to field test various control alternatives including suction removal and bottom barriers. Agency executives from the TRPA, NDSL, TRCD, USFWS,
LRWQCB and the CTC directed the LTAISWG and the UCD-UNR science team to begin development of these pilot removal investigations and to develop a science plan to evaluate these actions and provide managers with the knowledge needed to devise a full-scale management plan. The SNPLMA Round 10 proposal submitted on behalf of this UCD-UNR team proposed and carried out research based on this effort, with an abundance of data collected and presented herein. This current SNPLMA proposal is being submitted as an extension of the described management efforts based on the past year’s research findings.
In addition, this proposal is directly related to the conservation element of the TRPA regional plan update.
Specifically, as cited in the wildlife and fisheries subelement, this proposal lends directly towards the continued work with state and federal managers in the response to aquatic invasive species through the study of implemented management actions. Additionally, there is a nearshore component to the TRPA regional plan update. While the details of this component have not been supplied to the public by the
TRPA, the Asian clam populations of Lake Tahoe are already having an impact to the nearshore water clarity via algal growth stimulation, and the deposition of shell matter. The efficient management and reduction of Asian clam populations has the potential to remediate these impacts to the Tahoe nearshore. g. Strategy for engaging with managers and obtaining permits
Informally we will be in close contact with the LTAISWG and the LTAISCC as the Asian clam management project continues in 2010. We will formally engage managers by continuing to have monthly (and sometimes weekly) meetings with the Asian Clam Working Group (ACWG), which is comprised of representatives from TRPA, TRCD, USFWS, USACE, CADFG, USDA-ARS, CA State
Parks, LRWQCB, NDEP, NDOW, NDSL, TWSA, and by presenting quarterly updates in either as oral presentations or in written format to the LTAISWG, LTAISCC and the ACWG. When requested we will convene one technical and one public outreach meeting in collaboration with agencies and local organizations each year. Results from our project and reviews of other useful information related to Asian clam ecology and management will be posted on the UCD website (terc.ucdavis.edu) and the UNR website (environment.unr.edu). Results of the research will also be presented at the biennial Tahoe
Research Symposium, to be held in March 2010. Given the experimental endeavors of 2009, the permit acquisition structure is currently in place and functioning via the actions and relationships between UCD,
UNR, the TRCD, TRPA, NDEP and the TWSA. As of September 2009, all permits to conduct pilot removal activities have been renewed and are in good faith. h. Description of deliverables/products and plan for how data and products will be reviewed and made available to end users
There is an urgent need to develop a strategy for the efficient and effective implementation of research based Asian clam management pursuits in Lake Tahoe. Lake managers are seeking information on the efficacy of various control methods in managing clam populations. In this proposal we are providing critical information on the contribution of existing clam populations to the colonization of new areas, or the recolonization of treated areas in Lake Tahoe. In addition, we provide a framework for the implementation strategy for Asian clam treatment, with both biological and economic factors as the driving constraints for feasibility. The research group will continue to be in direct communication with lake managers and agency representatives of all levels to inform them of biological findings that relate directly to management of this invasive species. We will provide quarterly progress reports, a preliminary report (end of first year), and a final report (end of project). As part of this project we also expect to make presentations at annual scientific meetings (e.g. ASLO, ESA, regional meetings), submit manuscript(s) for publication in academic journals, and make public presentations of data as requested.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
III. Schedule of major milestones/deliverables
Milestone/Deliverables Start Date End Date Description
Submit quarterly progress reports
Objective 1, 2: Field collections
June 2010 May 2012 Submit brief progress report to Tahoe
June 2010 October
2011
Science Program coordinator on quarterly basis.
Field collections for deepwater clam beds at Nevada Beach to assess population, benthic diversity, clam fecundity, growth experiments—parameters establishing establishment and growth. Pre-rubber barrier application baseline characterization and post barrier application recolonization monitoring.
Objective 1, 2: Lab processing November
2010
January
2012
Process samples in laboratory for recolonization and economic model development
Objective 3: Data processing and Model development, Final reporting
Present quarterly updates to the LTAISWG, LTAISCC,
ACWG and relevant agencies
October
2011
May 2012 Data processing and modeling
Final Report
June 2010 May 2012 Present brief updates to the LTAISWG,
LTAISCC and ACWG at regular meetings, call a special meeting if needed to present information that may help managers develop control methods for
Asian clams
October
2011 proposed research. This report will be written specifically to aid managers and agency representatives in the decisionmaking for AIS management in Lake
Tahoe. This will include both biological assessment of Asian clam management and the presentation of associated costs.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
IV. Literature cited
Brown JH, Kodric-Brown A. 1977. Turnover rates in insular biogeography—effect of immigration on extinction. Ecology 58:445–449.
Byappanahalli MN, Shively DA, Nevers MB, Sadowsky MJ, Whitman RL. 2003. Growth and survival of
Escherichia coli and enterococci populations in the macro-alga Cladophora (Chlorophyta) FEMS
Microbiology Ecology 46 (2003): 203-211.
Cataldo D, Boltovskoy D. 1998. Population dynamics of Corbicula fluminea (Bivalvia) in the Paraná river delta (Argentina). Hydrobiologia, 380(1/2):153-163.
Davies JM, Hecky RE. 2005. "Initial Measurements of Benthic Photosynthesis and Respiration in Lake
Erie," Journal of Great Lakes Research 31(2):195-207.
Dobson AP, May RM. 1986. Patterns of invasions by pathogens and parasites. In: Mooney HA; Drake,
JA, eds. Ecology of biological invasions of North America and Hawaii. New York: Springer-
Verlag.
Hobbs RJ, Humphries SE. 1995. An integrated approach to the ecology and management of plant invasions. Conservation Biology 9(4): 761-770.
Holt RD. 2003. On the evolutionary ecology of species' ranges. Evol Ecol Res 5:159–178.
Liebhold AM, Sharov AA, Tobin PC. 2007. Population biology of gypsy moth spread. Pp. 15-32 in
“Slow the Spread: A national program to manage the gypsy moth” (P.C. Tobin and L.M.
Blackburn, eds.) USDA Forest Service Northern Research Station General Technical Report
NRS-6.
Krkošek M, Lewis MA. Lewis. 2009. An R
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theory for source sink dynamics with application to
Dreissena competition. Theoretical ecology. Online publication May 2009.
DOI 10.1007/s12080-
009-0051-7.
Mackie GL, Gibbons WN, Muncaster BW, Gray IM. 1989. The Zebra Mussel, Dreissena polymorpha : A synthesis of European experiences and a preview for North America. Water Resources Branch,
Great lakes Section, Ontario Ministry of the Environment, Toronto, Ontario.
Mattice JS, McLean RB, Burch MB. 1982. Evaluation of short-term exposure to heated water and chlorine for control of the Asiatic clam ( Corbicula fluminea ). Oak Ridge National Laboratory,
Environmental Science Division, Publication No. 1748. U.S. National Technical Information
Service, Department of Commerce, Springfield, VA, 33 pp.
Matthews MA, McMahon RF. 1999. Effects of temperature and temperature acclimation on survival of zebra mussels ( Dreissena polymorpha ) and Asian clams ( Corbicula fluminea ) under extreme hypoxia. J. Moll. Stud. 65: 317–325.
McMahon RF. 1983. Ecology of an invasive pest bivalve; Corbicula. In: The Mollusca, 6: Ecology.
(W.D. Hunter, ed.), 505-561. Academic Press, Orlando, Florida.
McMahon RF. 1999. Invasive characteristics of the freshwater bivalve, Corbicula fluminea . In : Claudi,
R., Leach, J. H. Eds. Nonindigenous freshwater organisms: vectors, biology and impacts. Lewis
Publishers, Boca Raton, FL, pp. 315-343.
McMahon RF, Bogan AE. 2001. Mollusca: Bivalvia. Pages 331-429 in J. H. T. a. P. Covich, editor.
Ecology and classification of North American freshwater invertebrates. Academic Press, San
Diego, CA.
McMahon RF, Lutey RW. 1988. Field and laboratory studies of the efficacy of poly[oxyethylene(dimethyliminio)ethylene(dimenthyliminio)ethylene dichloride] as a biocide against the Asian clam, Corbicula fluminea.
In : Proceedings: service water reliability improvement seminar. Electric Power Research Institute, Palo Alto, CA, pp. 61-72.
Mikheev VP. 1964. Mortality rate of Dreissena in anaerobic conditions. In: Biology and control of
Dreissena (B.K. Shtegmen, ed.), 65-68. Israel Program for Scientific Translations, Ltd., IPST Cat.
No. 1774, Jerusalem, Israel.
Nanbu R, Yokoyama E, Mizuno T, et al. 2007. Larval settlement and recruitment of a brackish water clam, Corbicula japonica , in the Kiso estuaries, central Japan. American Malacological Bulletin
22(1-2):143-155.
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Peck SK, Pratt WL, Pollard JE, Paulson LJ, Baepler DH. 1987. Benthic invertebrates and crayfish of Lake
Mead. Lake Mead Limnological Research Center, Environmental Research Center, University of
Nevada-Las Vegas. 93 p.
Pulliam HR. 1988. Sources, sinks, and population regulation. American Naturalist 132:652–661.
Shigesada N, Kawasaki K, Takeda Y. 1995. Modeling stratified diffusion in biological invasions.
American Naturalist. 146: 229-251.
Sousa R, Antunes C, Guilhermino L. 2008. Ecology of the invasive Asian clam Corbicula fluminea
(Muller, 1774) in aquatic ecosystems: an overview. Annales De Limnologie International Journal of Limnology 44:85-94.
Williams CJ, McMahon RF. 1986. Power station entrainment of Corbicula fluminea (Müller) in relation to population dynamics, reproductive cycles and biotic and abiotic variables. American
Malacological Bulletin Special Edition No. 2: 99-111.
Wittmann M et al. 2008. “Development of Asian clam control and monitoring plan strategies for Lake
Tahoe. Submitted to the Tahoe Regional Planning Agency.
Wittmann M, Chandra S, Caires A, Denton M, Rosen MR, Wong WH, Teitjen T, Turner K, Roefer P,
Holdren C. 2009. Early invasion population structure of quagga mussel and associated benthic invertebrate community composition on soft sediment in a large reservoir. Lake Reservoir
Management. Submitted.
Zipkin EF, Kraft CE, Cooch EG, Sullivan PJ. 2009. When can efforts to control nuisance and invasive species backfire? Ecological Applications. 19(6) 1585-1995.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
V. Figures
Figure 1. A schematic of the theoretical relationship between the abundance of an invasive species over time in relation to management stage (Hobbs and Humphries 1995). When population numbers are low early in a species invasion, the rate of invasive species abundance changes slowly because of limits to reproductive capacity per unit time. These low abundance periods occur during an invasion where quarantine, eradication and control are priorities for managers because of the potential for management when invasive species abundance is low. Once populations have increased over an extended amount of time, effective control is unlikely without massive resource inputs.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
Figure 2.
Distribution of Asian clam in Lake Tahoe: LEFT: A map of the distribution of Asian clam population density as indicated by benthic grab sampling (PONAR) efforts in 2008. RIGHT: Preliminary results of Gavia AUV lakewide survey. Red marks indicate Asian clam presence, blue marks indicate no
Asian clam presence. Note indications of Asian clam along the east shore, and north of Zephyr Cove.
Figure 3. Results from a deepwater Gavia autonomous underwater vehicle (AUV) survey at Nevada
Beach, Lake Tahoe. The red and blue markers represent the percentages of high resolution imagery frames that have identified objects as Asian clam. Benthic surveys carried out in 2009 correlate with these findings to indicate Asian clam presence from 8 to 80 m depth.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
Figure 4.
Benthic invertebrate distribution in Marla Bay (area of high Asian clam density) and in Zephyr
Cove (area of Asian clam presence, but lesser density than Marla Bay). Asian clam dominates benthic macroinvertebrates in Marla Bay, and can achieve densities as high as 5000 individuals per m
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Figure 5.
Dissolved oxygen concentrations (in mg/L) under an inverted chamber (box), a rubber barrier, and under a plastic barrier. Dissolved oxygen concentrations reduce to zero after 72 hours under the inverted chamber, after 36 hours under the rubber barrier and never under the plastic barrier.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
Figure 6. Numbers of live and dead Asian clams measured on a weekly basis under rubber botttom barriers. Green circles indicate live Asian clams, blue circles indicate dead Asian clams. The size of each circle indicates the abundance of clams found in each plot.
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