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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

Julia Randall

Senior Thesis

Middlebury College

January 27, 2005


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Goals and Predictions Algal Communities in a New England Salt Marsh

  • 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.


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Sampling Methods Algal Communities in a New England Salt Marsh

  • 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


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  • Current species counts: Algal Communities in a New England Salt Marsh

  • 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 l.jpg
Results: Microalgae Algal Communities in a New England Salt Marsh

  • 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


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Results: Microalgae Algal Communities in a New England Salt Marsh

  • 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


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Results: Microalgae Algal Communities in a New England Salt Marsh

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 l.jpg

  • Navicula Algal Communities in a New England Salt Marsh 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 l.jpg
Results: Macroalgae Algal Communities in a New England Salt Marsh

  • 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 l.jpg
Results: Macroalgae Algal Communities in a New England Salt Marsh

  • 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.


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Results: Macroalgae Algal Communities in a New England Salt Marsh

  • 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.


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Results: Macroalgae Algal Communities in a New England Salt Marsh

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.


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Conclusions Algal Communities in a New England Salt Marsh

  • 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.


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Acknowledgments Algal Communities in a New England Salt Marsh

  • 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


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