Term of Award

Fall 2011

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Department

Department of Biology

Committee Chair

Risa Cohen

Committee Member 1

Scott Harrison

Committee Member 2

Danny Gleason

Abstract

Short-term and seasonal variation in abiotic factors such as salinity, nutrient concentration, and light availability strongly influence total phytoplankton biomass but less is known about their effects on species-level changes due to difficulties associated with identifying and enumerating individual taxa. Understanding taxon-specific shifts is important as species often contribute differently to primary productivity and food web support for higher trophic levels. The goals of this study were to examine changes in overall phytoplankton abundance and community composition following short-term increases in freshwater input (Chapter 1), seasonal variation in abiotic conditions (Chapter 2), and manipulated nutrient concentrations within the Skidaway River Estuary (Chapter 3). Both microscopy and molecular analysis were used to examine species make-up. To characterize short-term and seasonal variation in the phytoplankton assemblage, three, two-week intensive field samplings were conducted following rain events of different magnitudes and in different seasons. During each sampling event, total phytoplankton abundance and species composition were determined twice daily at high and low tide along with abiotic measurements of salinity, temperature, light attenuation, and nitrate concentration. To examine estuarine phytoplankton community response to increased nutrients under manipulated conditions, phytoplankton from the SKE were exposed to either nutrient enrichment (phosphorous and/or nitrogen addition) or control treatments. Within and among all sampling periods the phytoplankton community was dominated by large diatoms including Coscinodiscus and Nitzschia species, and other taxa including chlorophytes like Nannochloropsis and dinoflagellates like Gymnodinium were more common in Spring. Salinity explained most of the variation in phytoplankton abundance and species composition and there were also positive relationships between the abundance of dominant species and temperature, light attenuation, and nitrate concentration, river discharge, and rainfall.

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