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The Effects of Nutrient Enrichment and Predator Removal on Algal Communities in a New England Salt Marsh. Julia Randall Senior Thesis Middlebury College January 27, 2005. Goals and Predictions. My goals: Effects of nutrient enrichment on algal communities in salt marsh creeks

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The Effects of Nutrient Enrichment and Predator Removal on Algal Communities in a New England Salt Marsh


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The Effects of Nutrient Enrichment and Predator Removal on Algal Communities in a New England Salt Marsh

Julia Randall

Senior Thesis

Middlebury College

January 27, 2005

goals and predictions
Goals and Predictions
  • My goals:
    • Effects of nutrient enrichment on algal communities in salt marsh creeks
    • Effects of predator removal on these same algal communities
  • Why algae?
    • Primary producers affect system as a whole
    • Should respond quickly to treatments
  • Predictions
    • Nutrient enrichment will increase algal biomass and decrease algal species richness.
    • Predator removal will decrease algal biomass.
sampling methods
Sampling Methods
  • Sampled two types of algal communities
    • Benthic microalgae
      • Slide rack colonization for density and species composition
    • Filamentous macroalgae
      • Biomass core
      • Strip of algae for species composition
sampling methods4

Current species counts:

  • Microalgae: 62 species
  • Macroalgae: 29 species
Sampling Methods
  • Sample processing
    • Microalgae: counted number of individuals per species on slides
    • Macroalgae: cores cleaned, looked through for species composition, dried and weighed.
results microalgae
Results: Microalgae
  • No significant response to predator removal. Why?
    • Slide placement
    • No evidence of grazing

Average density of microalgae on colonized slides

Possible interactions between treatments?

  • No significant response to nutrient enrichment. Why?
    • Silicon limited
    • Too short a time frame
results microalgae6
Results: Microalgae
  • No response to predator removal. Why?
    • Slide Placement
    • No evidence of grazing

Microalgal species richness on colonized slides

  • In +N, the richness is higher in August than in June.
    • Unusual but not impossible
    • Diversity
results microalgae7
Results: Microalgae

June

August

+N-F

2.26

2.31

+N+F

2.52

2.38

C-F

2.16

1.86

C+F

2.18

1.77

Species Diversity

(Shannon-Wiener Index)

results microalgae8

Navicula spE

    • Decreased density
    • Possible indicator of eutrophic conditions
  • Pleurosigma sp and Gyrosigma sp
    • Densities increased
    • Larger, motile cells favored by eutrophic conditions
Results: Microalgae
  • Responses of certain species of microalgae to nutrient enrichment
  • More information on nutrient requirements of individual species is needed
results macroalgae
Results: Macroalgae
  • No response to nutrient enrichment. Why?
    • Time frame
    • Pathway of nitrogen through system

Biomass of filamentous macroalgae from cores

  • No response to predator removal. Why?
    • Mummichogs forage on marsh platform.
results macroalgae10
Results: Macroalgae
  • No response to nutrient enrichment
    • Diversity is the issue
    • Species not driven to local extinction

Species richness of filamentous macroalgae

  • No response to predator removal
    • Mummichogs forage on marsh platform.
results macroalgae11
Results: Macroalgae
  • Enteromorpha spp.
    • Documented positive response to enrichment
    • In this study, it was found in both +N and C creeks.

Individual trends of macroalgal species in response to nutrient enrichment

  • Fucus spp
    • Documented negative response to enrichment
    • In this study, it was found only in the C creek.
results macroalgae12
Results: Macroalgae

Species composition of filamentous macroalgae

  • Response to nutrient enrichment:
    • West creek (C) has a similar August species composition to Clubhead creek (Ctrl).
    • Sweeney creek (F) has a different August species composition.
conclusions
Conclusions
  • No significant change in microalgal density and species richness, or in macroalgal biomass and species richness in response to either treatment.
  • Species diversity of microalgae appeared to be affected by the combination of treatments.
  • Species composition in filamentous macroalgae changed in response to nutrient enrichment, but not predator removal
  • Predictions
    • Changes in species composition and biomass of both macro- and microalgae are expected as a result of nutrient enrichment.
    • It cannot be predicted from our data whether predator removal will have any effect in future seasons.
    • The next two years of treatment and sampling should clarify responses of the system to the manipulations.
acknowledgments
Acknowledgments
  • Kari Galvan for giving this presentation!
  • Vermont Genetics Network and Middlebury College Biology Department, and Middlebury College Senior Work fund
  • TIDE project
  • Sallie Sheldon
  • MBL: Linda Deegan, David Patterson
  • Marshview people: Mike Johnson, Christian Picard, Catherine Sutera, and especially Kari Galvan
  • Middlebury people: Katie Harrold, Anna Strimaitis, Andi Lloyd, Steve Trombulak, and the rest of the BI 500 team
  • Others: Eric Randall and Jessica Dumont