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Biotic controls on microbial communities in estuarine and riverine habitats . Trisha Pascal-Lopez Microbial Ecology Lab, Mentors: Rima Franklin, Ph.D, and Amy Jenkins. Nutrient Input (ex. farm runoff) Algal Bloom (consumed by bacteria) Bacteria (hypoxia) Marine creature die

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slide1

Biotic controls on microbial communities in estuarine and riverine habitats

Trisha Pascal-Lopez

Microbial Ecology Lab,

Mentors: Rima Franklin, Ph.D,

and Amy Jenkins

slide2

Nutrient Input (ex. farm runoff)

  • Algal Bloom (consumed by bacteria)
  • Bacteria (hypoxia)
  • Marine creature die
  • Trophic cascade
slide3

A. Purpose

  • Study the ecological relationships that occur in an aquatic microbial food web
  • To understand the interdependence of three levels of the food web (phytoplankton, bacteria, and grazers)
  • Focus on response of bacteria to other community members

www.jerrygreerphotography.com/james_river_summer_reflection.htm

b setup
B. Setup

1) Two different initial environment samples:

  • James River mile 21 (Estuarine)
  • James River Rice Center (Riverine)

Courtesy of Paul Bukaveckas & River Ecology lab

slide5

B. Setup

2) Four treatments:

  • Manipulated light and dark levels
  • Eukaryotic growth inhibitor (cycloheximide)
  • 3 replicate of each treatment per environment, 3 day incubation
methods
Methods

1) Phytoplankton community:

  • Fluorescence detection of chlorophyll levels

2) Bacterial community:

  • Abundance (microscopic direct counts)
  • Culturability (counts of solid media/agar)
  • Genetic profiling (RAPD DNA fingerprints)

3) Grazer community:

  • Abundance and diversity (microscopic determination)
  • Mainly protozoa, rotifers and larvae

www.compucyte.com/pubbacterialdetection.htm

c results
C. Results

Estuary

site

Initial comparison

  • Distinct communities at start of experiment
  • Estuary had lower phytoplankton, grazer and bacteria abundance than riverine site (Rice).

Rice

Center

slide8

Were the treatments effective?

  • Changes to the phytoplankton population (greater for estuary)
  • Affected estuary & riverine phytoplankton differently
  • Reduced grazer abundance
  • Grazers linked to phytoplankton?
  • Decrease in grazer diversity
slide9

How did bacteria respond to the changes

in the phytoplankton and grazer abundance/ diversity?

Estuary: Bacteria abundance not linked to phytoplankton or grazers abundances (unaffected in all treatments).

Rice Center (Riverine): Treatments had an effect on bacterial community.

slide10

Light

+ cyclohex.

Dark

+ cyclohex.

Light

Dark

Light

+ cyclohex.

Dark

+ cyclohex.

Light

Dark

Changes in bacterial community composition?

Estuary: Community composition similar in all treatments

River: Changes in bacterial community with each treatment.

implications
Implications
  • Microbial communities in the Estuarine and Riverine environments are different.
    • Estuarine environment bacterial communities are not linked to grazer or phytoplankton abundance
    • Riverine environment shows bacterial interactions with phytoplankton and grazer communities
  • Microbial community interactions vary depending on the environment which controls their response to environmental stress.
d future goals
D. Future Goals
  • Statistical analysis of data
  • Chemistry (Nitrogen and DOC)
  • Run the experiment again with changes
    • Add another mile marker
    • Collect water sample at different seasons or times of day
    • Manipulate nutrient concentration
slide13

Questions?

Thank You