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

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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  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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)

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

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