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ZOOPLANKTON LIFE CYCLES: DIRECT DOCUMENTATION OF PELAGIC BIRTHS AND DEATHS RELATIVE TO DIAPAUSING EGG PRODUCTION
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).
Impact/Purpose:
The primary objectives of this research are to:
Develop methodologies so that landscape indicator values generated from different sensors on different dates (but in the same areas) are comparable; differences in metric values result from landscape changes and not differences in the sensors;
Quantify relationships between landscape metrics generated from wall-to-wall spatial data and (1) specific parameters related to water resource conditions in different environmental settings across the US, including but not limited to nutrients, sediment, and benthic communities, and (2) multi-species habitat suitability;
Develop and validate multivariate models based on quantification studies;
Develop GIS/model assessment protocols and tools to characterize risk of nutrient and sediment TMDL exceedence;
Complete an initial draft (potentially web based) of a national landscape condition assessment.
This research directly supports long-term goals established in ORDs multiyear plans related to GPRA Goal 2 (Water) and GPRA Goal 4 (Healthy Communities and Ecosystems), although funding for this task comes from Goal 4. Relative to the GRPA Goal 2 multiyear plan, this research is intended to "provide tools to assess and diagnose impairment in aquatic systems and the sources of associated stressors." Relative to the Goal 4 Multiyear Plan this research is intended to (1) provide states and tribes with an ability to assess the condition of waterbodies in a scientifically defensible and representative way, while allowing for aggregation and assessment of trends at multiple scales, (2) assist Federal, State and Local managers in diagnosing the probable cause and forecasting future conditions in a scientifically defensible manner to protect and restore ecosystems, and (3) provide Federal, State and Local managers with a scientifically defensible way to assess current and future ecological conditions, and probable causes of impairments, and a way to evaluate alternative future management scenarios.
Description:
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