| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2005: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
Exotic species common carp (Cyprinus carpio) and red swamp crayfish (Procambarus clarkii) modify communities and ecosystems as keystone species and exotic ecosystem engineers. We examined whether different densities of carp and crayfish have different impacts, and compared their density-dependent effects. Using an enclosure experiment, we investigated the relationships between carp or crayfish density and water quality, phytoplankton, nutrient dynamics, submerged macrophytes (the establishment of seeding from seed bank), zooplankton, benthic macroinvertebrates and sediment organic matter. We hypothesize that the relationship between density and response variable are either : (i) linear or (ii) non-liner (exponential saturated curve). Both carp and crayfish increased suspended solids (SS), inorganic suspended solids (ISS) and chlorophyll a (Chl.a), changed nutrient dynamics and decreased submerged macrophytes and benthic macroinvertebrates, although only carp affected on zooplankton and
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sediment organic matter. However, carp and crayfish showed different density-dependent effects. The relationships between SS,ISS,Chl.a,NH_4-N and Chironominae response to carp density were non-linear, indicating that carp have strong effects on these variables at even low density. In contrast, crayfish have a large negative effect on submerged macrophytes and the relationship was non-linear. The observed effects of carp and crayfish on these variables were probably due to a combination of bioturbation, excretion and predation, suggesting that ecosystem engineering may have pronounced impactson other community members. Also, differences in their impacts were related to functional uniqueness. We also demonstrate that an introduction of exotic ecosystem engineer such as carp and crayfish may trigger a shift from a clear water state with abundant macrophytes to a turbid state dominated by phytoplankton. Our results provide important implications for strategies to eradicate carp and crayfish. Although eliminating these species as much as possible is the best management practice for conservation and restoration of native biodiversity and ecosystem, we propose that it gives first priority to remove crayfish to conserve macrophytes. Less
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