| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | January 24, 2017 |
| Latest Amendment Date: | February 4, 2022 |
| Award Number: | 1657314 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Cynthia Suchman
csuchman@nsf.gov (703)292-2092 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | April 1, 2017 |
| End Date: | March 31, 2023 (Estimated) |
| Total Intended Award Amount: | $318,001.00 |
| Total Awarded Amount to Date: | $318,001.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
75 LOWER COLLEGE RD RM 103 KINGSTON RI US 02881-1974 (401)874-2635 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
215 South Ferry Road Narragansett RI US 02882-1197 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | BIOLOGICAL OCEANOGRAPHY |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Phytoplankton have an intimate connection to the hydrodynamic environment in which they live.
Previous studies have examined the role that turbulence and shear play in nutrient uptake, patch/layer formation, and predator-prey encounters, but the role of phytoplankton orientation to increase light capture (and ultimately primary production) has been largely overlooked. Compelling evidence of persistent horizontal orientation of chain-forming diatoms, obtained from novel in situ holographic imaging, has led to a hypothesis that in regions of strong stratification, shear flows will lead to systematic horizontal orientation of elongate phytoplankton forms that maximizes their cross-sectional area (and light capture) in the ambient downwelling light field. It has also been suggested that variations in phytoplankton size and shape are fundamental traits conferring selective competitive advantages in certain hydrodynamic environments, thus modifying/mediating community composition. The interdisciplinary research of this project crosses three scientific disciplines (biology, optics and fluid dynamics) and will advance our understanding of the function of diverse forms of phytoplankton, their interactions with fluid flows, and the resultant impacts on the optics of the environment. The project will support a number of undergraduate and graduate students, and post-doctoral researchers.
This project combines analysis of previously collected field data with laboratory experiments and modeling. For the field data analysis, phytoplankton orientation is quantified from in situ holographic images of the undisturbed water column along with concurrent high resolution measurements of critical physical (turbulence/shear/stratification) and optical parameters collected from a ship-based holographic bio-physics profiler. In the laboratory, the orientation response of different phytoplankton species and morphologies is evaluated in custom built shear tanks under controlled laminar and turbulent conditions to confirm that elongate forms can orient in certain hydrodynamic environments to maximize light capture. In addition, controlled growth/physiology experiments in various shear tank treatments will explore the effects of orientation on growth, photosynthetic parameters and productivity. Lastly, the project results will be incorporated into a global analysis of observed and modeled physical, bio-optical and ecologically-relevant parameters, to quantify the relevance of this phenomenon to primary production and the carbon cycle.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The overarching goal of our collaborative project is to investigate whether horizontal orientation of elongate phytoplankton cells and colonies within typical oceanic shear flows enhances their light harvesting abilities in light limited environments, thus conferring a competitive ecological advantage. Our approach included innovative laboratory experiments, custom-designed instrumentation and analysis of field data.
To evaluate our hypothesis in the laboratory, uni-algal isolate of Stephaopyxis turris was grown under controlled conditions simultaneously for three different rotation rates in the Couette chamber. Holographic imaging was used to determine colony orientation, length, and concentration over 25 days. Holograms were reconstructed at 1 mm intervals and an extended depth of field image with all colonies in focus was generated by combining reconstructed planes. Laminar and turbulent cases showed an increase in individual diatom chains across the experiment. Higher growth rates were achieved in the turbulent case compared to the laminar case, consistent with previous studies.
Our study was unique in the ability to determine the orientation of the diatom chains in these different flows. Our lab studies clearly showed that strong preferential horizontal orientation was seen in the laminar case. We further sub-sampled the diatoms according to their aspect ratios (ratio of major axis to minor axis). Once diatom chains are segregated according to their aspect ratio, the trends again became clear. In the laminar case, stronger horizontal preferential orientation with increasing aspect ratio was seen. On the other hand, there was no discernable difference in the turbulent case. All orientation results discussed here agreed very well with field observations by our group as well as with theory.
Modeling and field studies were conducted that focused on the optical effects of phytoplankton orientation and the potential effects on light harvesting. In situ measurements of diatom colony orientation previously acquired with a HOLOCAM instrument were used to model their light absorption efficiency. A geometric optics based modeling approach was used for its ability to accommodate populations of large particles of various size and aspect ratio. Modeling of phytoplankton absorption was performed for several estimated intracellular chlorophyll concentrations over a continuous profile from the surface to ~25 m depth. Holographic images revealed a thin layer of Ditylum brightwellii with strong horizontal orientation. Orientation of colonies in this thin layer enhanced their absorption by up to 24.5% verifying our study hypothesis.
Last Modified: 06/18/2024
Modified by: Melissa Omand
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