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Zooplankton Life Cycles: Direct Documentation of Pelagic Births and Deaths Relative to Diapausing Egg Production

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Abstract:Full-season demographics (pelagic births and deaths, diapause egg production) provide valuable insights into species persistence and dispersal success. The spiny cladoceran (Bythotrephes) possesses morphological adaptations (spines and thick-walled diapause eggs) that lessen impacts of fish predation, although the seasonal life history remains vulnerable. Because caudal spines are retained throughout life, spine accumulation in sediment traps documents seasonal mortality. Here we compare deposition patterns for spines and diapause eggs in a recently colonized inland lake (Lake Michigamme) with patterns found in a larger source lake (Lake Michigan). Direct mortality estimates for the inland lake are compared with traditional indirect estimates from egg ratio techniques. Although the long caudal spine protects against numerically abundant small fish, individuals are susceptible to ingestion by late-season YOY and larger fish. Laboratory experiments confirm that fish are responsible for spine breakage in nature accounting for an estimated 62-73% of Bythotrephes' seasonal mortality. The impact of late- season fish consumption is lessened because diapause eggs survive gut passage. Nonetheless, relatively few diapause eggs are produced in the inland lake. Sequential sediment traps document a more balanced pelagic birth/death to diapause egg relationship in Lake Michigan, probably because diapause egg-bearing adults find better refuge in central, deep waters. The presence of spines and thick-walled eggs inadvertently creates numerous dispersal options. Spines catch on fishing lines, gill nets and seines. Because diapause eggs survive gut passage, use of live wells and bait fish also promotes dispersal, although high fish predation at inland sites probably limits successful inland colonization

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Citation:Jarnagin, S. T., W. C. Kerfoot, and B. K. Swan. Zooplankton Life Cycles: Direct Documentation of Pelagic Births and Deaths Relative to Diapausing Egg Production. LIMNOLOGY AND OCEANOGRAPHY 49(4, part 2):1317-1332, (2004).
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Contact: Chris Siebert - (702) 798-2234 or siebert.christopher@epa.gov
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Division: Environmental Sciences Division
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Branch: Landscape Ecology Branch
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Product Type: Journal
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Published: 06/29/2004
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Related Entries:
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Bullet Item Development of Landscape Indicators for Use in Regional Ecological Risk Assessments
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