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Implications of Cercopagis and Bythotrephes to alewife recruitment andstability of the Lake Michigan pelagic food web

We have examined prey selection and feeding of the invading predatory  cercopagid cladocerans Cercopagis pengoi and Bythotrephes longimanus  useful for predicting predatory impact on zooplankton. We will combine  this information with field observations  of population dynamics, production and spatial distribution of  zooplankton and fishes to describe  and understand invasion dynamics of Cercopagis. We hypothesized that  alewife predation on Bythotrephes, a competitor and predator of  Cercopagis, has allowed Cercopagis to invade nearshore waters of the  spatially complex Lake Michigan.  We analyzed results of a 2  4  experiment to evaluate time varying spatial coupling and predatory  interactions among fish, Bythotrephes, Cercopagis, and other  zooplankton over the diel cycle. We did intense diel of sampling  (every four hours) of: zooplankton distribution by net tows, pumping,  and plankton survey system; fish distribution by acoustics; and fish  in trawls for diet analyses at a deep and shallow stations near  Muskegon MI during a full moon and new moon to determine spatial and  predatory interactions among Bythotrephes, Cercopagis, alewives, and  zooplankton. Results showed that alewives fed throughout the day and  night, heavily selecting Bythotrephes, and strongly avoiding  Cercopagis.  Inshore, predation of alewives on Bythotrephes was higher  than Bythotrephes production, and predation on Cercopagis was much  lower than production (Pothoven et al. 2  7). Offshore, there were no  Cercopagis, and preliminary estimates suggested that alewife predation  took only a small fraction of Bythotrephes production because fish  biomass was lower Bythotrephes. Detailed coupling between fish and  prey was shown by plankton survey systems and size categories were  assigned. Zooplankton in the large Daphnia size range showed strong  vertical migration with the population stratifying in relatively  narrow depth strata during the day that did not overlap with fish or  Bythotrephes sized particles.  Vertical distribution of "Daphnia"  varied great between cruises because of depth of thermocline and its  structure. In general they selected the lower metalimnion or upper  hypolimnion. These same trends were seen with net tow data sampling  the broad epi-, meta-, and hypolimnetic regions.  Work in 2  8 will  focus on refining estimates of alewife predation in the offshore  region and the factors that regulate it.

Status
In progress
Type
Project
Start Date
End Date
Scope of Study
Field Investigation
Laboratory Investigation
Scale of Phenomena
Ecosystem
Impact of Pollutants
Exotic Species
Processes
Natural Ecological Processes
Lake Basin Connecting Channels
Lake Michigan
Purpose of Project
Special Survey
Trend Assessment
Resource Being Monitored
Wildlife
Biology And Life History
Population Dynamics
Control And Mitigation
Habitat Manipulation
Ecosystem Effects
Food Web Structure
Prevention and Introduction
Identification of Potential Invaders
Spread of Established ANS Populations
Mechanisms of Spread
Annex Numbers
Research & Development
Annex 17
Impact of water quality and AIS on fish and wildlife populations and habitats
General
Aquatic Nuisance Species
Annex
  • Annex Numbers
    Annex Numbers
    Research & Development
  • Annex 17
    Annex 17
    Impact of water quality and AIS on fish and wildlife populations and habitats

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