Seagrass transplant success linked to sediment bacterial community composition

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Seagrass transplant success linked to sediment
bacterial community composition

• Eric Milbrandt
• Sanibel-Captiva Conservation Foundation

27 March 2008 Charlotte Harbor Summit Punta
Gorda, FL
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Background and Justification

• Widespread losses, declines in density, and
  changes in distribution of seagrass communities
  occur as the result of natural and anthropogenic
  activities
• Attempts to restore seagrass habitats through
  bare-root vegetative transplants have met with
  limited success
• Why? Complex interactions mediating seagrass
  health
• environmental conditions (Thorhaug 1985, Lewis
  1987, Molenaar and Meinesz 1995, Fonseca et al.
  1998)
• biogeochemical aspects of the sediment (Koch
  2001)

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Phase I Field Experiment

• Purpose - to disrupt sediment bacteria and
  examine the effects on early transplant survival

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Transplant Methods

• Plants were removed from the area to be dredged,
  then separated from the sediments
• Blade length, blade width, the number of blades
  per shoot
• Sediments from each treatment were sub-sampled
  for microbial analysis

Measuring the seagrass leaves before transplanting
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Response Variables

• Growth of transplants relative to naturally
  growing plants
• Survivorship in a 3 month monitoring period
• Microbial diversity analysis at the start
  (response to sterilization treatment) and at the
  end of monitoring

Individually marked transplant
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Response to treatments
Steam treated sediment bacteria communities were
significantly disrupted
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Disruption caused higher mortality
Disruption caused higher mortality
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Results (cont.)
Bacterial community composition was similar among
survivors
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Additional research

• Details can be found in Milbrandt, E.C., J.M.
  Greenawalt, P.D. Sokoloff, in press, Short-term
  indicators of seagrass transplant stress in
  response to rhizosphere and bacterial community
  disruption. Botanica Marina.
• Why is community composition critical to
  surviving transplant shock?

• Detoxify H2S or other phytotoxins
• Carbon and Nitrogen re-mineralization activities
  provide the ratio of necessary nutrients for
  growth, especially when transplanted

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Phase II Greenhouse

• Variables (light, salinity, temperature, DO) can
  be controlled in a laboratory experiment.
• Substrate and sulfide concentrations were
  manipulated

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Thalassia transplant growth rates
SA () Sulfide, () Autoclave SN () Sulfide, (-)
Autoclave NSA (-) Sulfide, () Autoclave NSN (-)
Sulfide, (-) Autoclave Control, not transplanted

• Growth rates significantly slower in autoclaved
  playsand than other treatments

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DNA Yield


SA () Sulfide, () Autoclave SN () Sulfide, (-)
Autoclave NSA (-) Sulfide, () Autoclave NSN (-)
Sulfide, (-) Autoclave Control, not transplanted

• DNA yield significantly lower in autoclaved
  playsand

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Bacterial community
SA () Sulfide, () Autoclave SN () Sulfide, (-)
Autoclave NSA (-) Sulfide, () Autoclave NSN (-)
Sulfide, (-) Autoclave Control, not transplanted

• No significant effect of treatment observed

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Conclusions

• Phase I Field experiment
• Manupulation of the root zone caused significant
  changes in bacterial community composition and
  decreases in transplant survival
• Whenever possible, seagrasses should be
  transplanted with substrate (GIGA 3m X 3m)
• Phase II Greenhouse experiment
• Elevated sulfide treatment had no measurable
  effect on transplant success
• Playsand decreased transplant survival, and
  should not be used in transplant projects (caused
  by a lack of bacterial colonization?)

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Acknowledgements

• Support
• SCCF Core Research Program
• FGCU Biotechnology Program
• CHNEP Research and Restoration Partners
• JN Ding Darling National Wildlife Refuge
• People
• Jaime Boswell-Greenawalt
• Paul Sokoloff
• Jon Guinn
• Jeff Siwicke
• AJ Martignette