James Evans1, Jennifer Nelson1, Bethany Bachelor1, Scott Burghart2, Greg Tolley1

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Influence of Freshwater Inflow on the Spatial and
Temporal Distribution of Ichthyoplankton and
Gelatinous Zooplankton in Estero Bay

• James Evans1, Jennifer Nelson1, Bethany
  Bachelor1, Scott Burghart2, Greg Tolley1
• 1Florida Gulf Coast University, Coastal Watershed
  Institute
• 2University of South Florida, College of Marine
  Science Estuarine Ecology Lab

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Research Objectives

• Determine the influence of freshwater inflow on
  the spatial and temporal distribution of
  ichthyoplankton and gelatinous zooplankton
• Assess the effect of freshwater inflow on
  ichthyoplankton and gelatinous zooplankton
  community structure
• Provide information to water managers to help
  determine optimal freshwater inflows for managing
  important aquatic resources

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The Study Area
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Survey Design

• Sampling effort
• Two-year zooplankton survey
• Monthly sampling frequency
• 16 fixed stations per month
• 1 plankton-net tow per station
• 1 water-quality profile per station
• 384 total samples

• Sampling Methods
• 500-µm mesh, 0.5 m diameter plankton net
• oblique tows, 5 min duration
• Water quality profiles surface (0.2 m), bottom
  and 0.5-m intervals
• Flow data from USGS monitoring stations
• Laboratory Methods
• Zooplankton identified to the lowest practical
  taxon
• Fishes classified according to their
  developmental stage

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Data Analysis

• Hydrographs, salinity contours, seasonal water
  quality
• Spawning habitat and season
• Contour plots of water quality organism density
• Density-weighted mean salinity of capture
• Community structure
• Seasonality of habitat use
• Abundance relationships with salinity as a proxy
  for freshwater inflow

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Freshwater Flow 2005-2006
1 month
Hydrographs using indexed inflow Sum of
Ten Mile Canal Estero River
(N S branches) Spring Creek
Imperial River
42
Inter-annual lag in onset of wet season
(June 2005 vs. July 2006) Total
inflow 42 higher in 2005
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Water Quality
Temperature
Dissolved Oxygen
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Salinity Distribution
February
March
April
May
June
July
August
September
October
November
December
January
2005
2006
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Likely Spawning Habitat
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Seasonal Spawning Patterns
Protracted spawning Anchoa mitchilli (bay anchovy)
Spring-Summer spawning Trinectes
maculatus (hogchoker)
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Density-weighted Mean Salinity of Capture
Fishes
S (SU) S U
Gelatinous Predators
SU
S (SU) S U
SU
S (SU) S U
SU
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Anchovy eggs Anchoa mitchilli
Medusa Eutima sp.
Salinity
Wet June (2005)
Dry June (2006)
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Community Structure Fishes June 2005 (Wet)
Community Structure Fishes June 2006 (Dry)
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Gelatinous Predators June 2005 (Wet)
Gelatinous Predators June 2006 (Dry)
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Seasonal Patterns
Anchoa mitchilli (bay anchovy)
Eutima sp.
High degree of interannual variability in density
for some species
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Inter-annual Variability
Clytia sp. bloom June at stations 9 10
Sagitta tenuis
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Conclusions

• Ichthyoplankton and gelatinous predator densities
  and community structure appear to be strongly
  influenced by freshwater inflow
• Ichthyoplankton demonstrated seasonal patterns
  -abundances greatest in spring and summer and
  peak abundances in March, coinciding with the
  spawning season for the most abundant taxa
• Gelatinous predators were displaced downstream
  during periods of high inflow and bloom in poorly
  circulating waters
• Reduced freshwater flow may increase predation
  rates and competition for prey items by
  gelatinous predators

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Management Implications Future Work

• Ernst Peebles and Greg Tolley developed a
  management tool for predicting the impact of
  reduced flows on indicator taxa identified during
  this study
• Data will be used to help establish an MFL for
  Estero Bay
• Future work - investigate the role of freshwater
  inflow on the trophic relationships between
  ichthyoplankton and gelatinous predators

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Acknowledgements

• FGCU - Coastal Watershed Institute
• Greg Tolley
• Erin Dykes Lesli Haynes
• USF College of Marine Science Estuarine Ecology
  Lab
• Ernst Peebles, Scott Burghart, and Ralph
  Kitzmiller
• SFWMD
• Peter Doering Bob Chamberlain
• USGS
• Ed Patino, Mike Byrne and Carolyn Price

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Questions?