Invasive clams in Lake Tahoe: Reproductive strategies and impacts to native benthic community structure
Natural Resources and Environmental Science
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Invasive species are of concern to ecologists and resource managers due to the growing ecological and economic impacts associated with their introduction. In North America, invasive species cause significant environmental impacts with costs estimates of $137 billion annually. Second to loss of habitat, invasive species have been linked to the declines in biodiversity on a global scale. Once established, invasive species have been shown to alter community and ecosystem dynamics, change habitat for native species, interrupt energy flow through food webs, and reduce ecosystem services. Among non-native aquatic species, invasive bivalves can cause significant impacts by altering the availability of resources, contributing to the extirpation of native species, declines in diversity and impairment of ecosystem functioning. They are able to tolerate a wide range of environmental conditions (temperature, water chemistry, substrate, etc.), allowing them to acclimatize to a new environments, making them adaptable to exploit ecological niches. In the last century, Corbicula fluminea (Asian clam) has been one of the more successful invasive bivalves to establish in aquatic ecosystems. C. fluminea is an invasive freshwater bivalve to North American that originally established in Pacific Northwest in 1938 from Southeast Asia, and has since been documented in 42 states. The shells of dead C. fluminea may provide refuge and substrate for the establishment of benthic larval insect communities and live clams may influence benthic communities by processes of bioturbation of sediment via burrowing and biodeposition of organic matter as feces and pseudofeces. Through highly efficient suspension-feeding and deposit- feeding on sediment organic matter, C. fluminea may also couple the pelagic and benthic food webs. The vectors of invasion are live bait buckets however the release of aquarium stock and transport via boat bilge is possible.Recently there has been an invasion of C. fluminea in Lake Tahoe, a large, deep subalpine lake located in the central Sierra Nevada of California and Nevada. Very little is known about the life history or impacts of clams on the ecology of the lake; however, preliminary research suggests they may linked to increased nearshore algal blooms. The chapters included here examine the reproductive strategies (Chapter 1) and impacts to native benthic community structure (Chapter 2) by C. fluminea in Lake Tahoe. In Chapter 1, it was determined that C. fluminea in Lake Tahoe had a low reproductive effort with a single spawn that occurred in late summer that is likely linked to the temperature and low food availability. Moreover, deeper water populations of clams are likely populations sinks dues due to the cold temperatures. Chapter 2 shows how C. fluminea changes benthic community structure depending on the level of infestation. It was determined that three taxa had greater abundances where abundances of C. fluminea are low. In areas with greater abundance, C. fluminea facilitate two taxa, Chironomidae and Trichoptera. While the mechanisms were not studied, the shells of clams may provide structure and thus habitat for certain invertebrates. Other mechanisms of facilitation such as competition or providing increased food supply through the release of pseudofeces may also impact community structure. Other behavioral experiments and raw data not formally presented in chapter form are presented in the Appendix. As the establishment of C. fluminea is still in an early stage of invasion, future studies and monitoring will be essential to further determine how the clam impacts Lake Tahoe's ecosystem.