Recipient Organization
UNIVERSITY OF NEVADA
(N/A)
RENO,NV 89557
Performing Department
Natural Resources & Environmental Sciences
Non Technical Summary
The invasive bivalve, Asian clam is established and spreading in Lake Tahoe. In 2002, low density populations (2-20 individuals per m2) were observed in the south eastern portion of the lake, and in 2009 densities up to 5000 individuals per m2 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). 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.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
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 human-mediated limitations to Asian clam in Lake Tahoe (i.e., control strategies), and subsequent recolonization. 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 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.
Project Methods
Objective 1. 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. 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. Objective 2. 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 SCUBA-based 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 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. 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 post-treatment, 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.