Presentation Title

Changes in the Microbial Community After the Addition of Nutrients and Zooplankton in Bottle Incubations

Faculty Mentor

Dr. Adriane Jones, Dr. Diane Kim

Start Date

17-11-2018 8:30 AM

End Date

17-11-2018 10:30 AM

Location

CREVELING 120

Session

POSTER 1

Type of Presentation

Poster

Subject Area

biological_agricultural_sciences

Abstract

Mesocosms or bottle incubations are enclosed environments that allow the natural environment to be observed under controlled conditions. The microbial food web is composed of both single celled eukaryotes and bacteria that can be photosynthetic or heterotrophic, which have complex interactions with each other. Microbial growth is affected by both nutrient availability (bottom up) and predator zooplankton grazing (top down). In this experiment, we manipulated the microbial food web on Catalina Island, California by adding nutrients (nitrate and phosphate) or nutrients plus zooplankton grazers (plankton >500 μm) into our bottles. We hypothesized that the addition of nutrients would increase the abundance of microbes and that the addition of zooplankton would have a negative impact. Seawater was collected from an intake pipe at the USC Wrigley Marine Science Center facility 30 feet below the surface. Triplicate incubation bottles were set up under three treatments: 1) control 2) nutrients and 3) nutrients plus zooplankton grazers. The bottles were incubated in an outdoor flow through seawater system located on Catalina from May 27-31 2018. Subsamples were collected daily for 1) bacteria cell counts, 2) eukaryotic cell counts, 3) nitrate measurements and 4) extracted chlorophyll on two sizes of filters GF/F (>0.7 μm), and GF/D (> 2.7 μm). Nitrate levels were higher in the two nutrient addition treatments (~12 μM) compared to the control (~6 μM), and remained constant in all three treatments throughout the course of the experiment. Bacterial abundances were 3-5 x 10^6 cells/ml and did not change across the treatments or throughout the experiment. Eukaryotic cells (~5 μm) increased with the addition of zooplankton grazers compared to the nutrients alone and the control. Chlorophyll concentration in the two experimental treatments increased in both size fractions 1) everything >0.7 μm and 2) cells > 2.7 μm. The chlorophyll concentration in the fraction that included the smallest cells >0.7 μm showed the greatest increase in both experimental treatments suggesting that the smaller size class phytoplankton had the greatest response to the amendments. Furthermore, the greatest increase in chlorophyll was found in the fraction that included the smallest cells >0.7 μm when amended with nutrients only suggesting that the zooplankton might be grazing on the cells in the 0.7 to 2.7 μm size range.

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Nov 17th, 8:30 AM Nov 17th, 10:30 AM

Changes in the Microbial Community After the Addition of Nutrients and Zooplankton in Bottle Incubations

CREVELING 120

Mesocosms or bottle incubations are enclosed environments that allow the natural environment to be observed under controlled conditions. The microbial food web is composed of both single celled eukaryotes and bacteria that can be photosynthetic or heterotrophic, which have complex interactions with each other. Microbial growth is affected by both nutrient availability (bottom up) and predator zooplankton grazing (top down). In this experiment, we manipulated the microbial food web on Catalina Island, California by adding nutrients (nitrate and phosphate) or nutrients plus zooplankton grazers (plankton >500 μm) into our bottles. We hypothesized that the addition of nutrients would increase the abundance of microbes and that the addition of zooplankton would have a negative impact. Seawater was collected from an intake pipe at the USC Wrigley Marine Science Center facility 30 feet below the surface. Triplicate incubation bottles were set up under three treatments: 1) control 2) nutrients and 3) nutrients plus zooplankton grazers. The bottles were incubated in an outdoor flow through seawater system located on Catalina from May 27-31 2018. Subsamples were collected daily for 1) bacteria cell counts, 2) eukaryotic cell counts, 3) nitrate measurements and 4) extracted chlorophyll on two sizes of filters GF/F (>0.7 μm), and GF/D (> 2.7 μm). Nitrate levels were higher in the two nutrient addition treatments (~12 μM) compared to the control (~6 μM), and remained constant in all three treatments throughout the course of the experiment. Bacterial abundances were 3-5 x 10^6 cells/ml and did not change across the treatments or throughout the experiment. Eukaryotic cells (~5 μm) increased with the addition of zooplankton grazers compared to the nutrients alone and the control. Chlorophyll concentration in the two experimental treatments increased in both size fractions 1) everything >0.7 μm and 2) cells > 2.7 μm. The chlorophyll concentration in the fraction that included the smallest cells >0.7 μm showed the greatest increase in both experimental treatments suggesting that the smaller size class phytoplankton had the greatest response to the amendments. Furthermore, the greatest increase in chlorophyll was found in the fraction that included the smallest cells >0.7 μm when amended with nutrients only suggesting that the zooplankton might be grazing on the cells in the 0.7 to 2.7 μm size range.