Abstract:
Fast repetition rate (FRR) fluorescence offers rapid measurement of photosynthesis in vivo, and is an effective tool for assessing stress responses in phytoplankton exposed to crude oil. Using natural phytoplankton communities collected from the Gulf of Mexico exposed to oil and the chemical dispersant Corexit, we measured fluorescence signals every 12 hours over 3 days using a Fluorescence Induction and Relaxation (FIRe) system.
Suggested Citation:
Laura Bretherton, Manoj Kamalanathan, Jennifer Genzer, Jessica Hillhouse, Antonietta Quigg. 2017. Fast repetition rate fluorescence responses of natural phytoplankton communities incubated for 3 days in a mesocosm experiment exposed to crude oil and chemical dispersants, July 2016. Distributed by: Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC), Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7NP22G2
Purpose:
The purpose of the coastal mesocosm experiment was to assess the response of natural microbial communities to crude oil and dispersant exposure. In order to monitor phytoplankton growth, chlorophyll fluorescence was measured using a fluorescence induction and relaxation (FIRe) system. This method allows for a multi-parameter assessment of phytoplankton photophysiology that can detect sub-lethal effects of oil and dispersants, and allow for better detection of oil and dispersant stress.
Data Parameters and Units:
Date (Month/Day/Year), Time Point (hours 0, 12, 24, 36, 48, 60, 72), Treatment (Control, WAF=water accommodated fraction, CEWAF=chemically enhanced water accommodated fraction, DCEWAF=diluted chemically enhanced water accommodated fraction), Replicate (A, B, C, FSW=filtered seawater, WAF, CEWAF, DCEWAF), Fo (baseline fluorescence, dimensionless), Fm (maximum fluorescence, dimensionless), Fv/Fm (photosynthetic quantum yield, dimensionless), sigma (functional absorption cross-section of photosystem II, Å^2/quanta), p (connectivity factor, dimensionless), tau1 (electron turnover time on acceptor side of photosystem II, µs), tau2 (electron turnover time between photosystem II and photosystem I, µs), chl-a (chlorophyll concentration by fluorescence, dimensionless)
Methods:
Natural seawater was collected from a coastal buoy in the Gulf of Mexico and brought back to Texas A&M University at Galveston for manipulation. Treatments were prepared in specialized glass tanks called WAF makers using the natural seawater. WAF treatments were prepared by adding Macondo crude oil to a target concentration of 1mg L-1, and CEWAF treatments were made with a stock solution containing a 20:1 ratio of oil:Corexit. One third of the CEWAF was then diluted until the crude oil concentration was consistent with the WAF to make the DCEWAF treatments. Control treatments were not exposed to either oil or Corexit. The experiments were then set up in 100L glass tanks staged in a room fitted with fluorescent bulbs. All treatments were grown in triplicate with true biological replication. A 4mL sample was retrieved from each tank every 12h over the course of 3 days. The samples were left to dark-acclimate for ~10 minutes before being transferred into the Fluorescence Induction and Relaxation (FIRe) system (Satlantic, Halifax, Canada). Parameters were collected from both single turnover (ST) and multiple turnover (MT) curves, using 60 acquisitions per sample to reduce noise. The sample was then recovered from the FIRe to measure the relative fluorescence intensity of chlorophyll-a using a Turner fluorometer (Turner Designs, San Jose, USA).
Instruments:
All data except chlorophyll concentration were collected using a Fluorescence Induction and Relaxation (FIRe) System (Satlantic, Halifax, Canada). Chlorophyll was measured with a 10AU Field Fluorometer (Turner Designs, San Jose, USA).
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