Abstract:

This work is a continuation of the Tier 1 screening process to identify species of phytoplankton that are sensitive and resilient to oil and Corexit exposure. Cultures were grown of Micromonas pusilla, Tetraselmis astigmatica, Ochromonas sp., and other groups of phytoplankton that are underrepresented in the literature, but still important to the ecology of the Gulf of Mexico. Measurements of growth dynamics and photophysiology help to ascertain how these organisms respond to oil pollution.

Suggested Citation:

Laura Bretherton, Andrew Irwin, Zoe Finkel, Antonietta Quigg. 2019. Physiological responses of marine phytoplankton exposed to oil and Corexit in culture experiments. Distributed by: Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC), Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-jehv-5771

Publications:

Bretherton, L., Hillhouse, J., Kamalanathan, M., Finkel, Z. V., Irwin, A. J., & Quigg, A. (2020). Trait-dependent variability of the response of marine phytoplankton to oil and dispersant exposure. Marine Pollution Bulletin, 153, 110906. doi:10.1016/j.marpolbul.2020.110906

Purpose:

This work was conducted to further understand what traits contribute to resistance to oil in marine phytoplankton. The species were selected to test a variety of traits such as motility, mixotrophy, cell size and the presence of a cell wall. This work can allow us to better predict how phytoplankton communities in the Gulf of Mexico might respond to future oil spills, and understand why different taxonomic groups respond so differently to oil exposure.

Data Parameters and Units:

Species: denotes the algal species the data is for (Mp = Micromonas pusilla; Ta = Tetraselmis astigmatica; Os = Ochromonas sp., Hp = Heterocapsa pygmaea; Pm = Prorocentrum minimum) Timepoint: units are in days Treatment: the conditions the culture was grown in (C = control, f/2 seawater media; O = WAF, Water Accommodated Fraction of oil; M = CEWAF, Chemically Enhanced Water Accommodated Fraction of oil; DM = DCEWAF, Diluted Chemically Enhanced Water Accommodated Fraction of oil) Replicate: each treatment was grown in triplicate, labelled A, B and C EOE: Estimated Oil Equivalents, oil concentration measured in mg/L Chl-a: Chlorophyll-a, measured in µg/L Fv/Fm: the photosystem II (PSII) quantum yield, dimensionless Sigma: PSII absorption cross-section, measured in Å2 (quanta)-1 p: PSII connectivity factor, dimensionless Tau1: time constant of photosynthetic electron transport on the acceptor side of PSII, measured in µs Tau2: time constant of photosynthetic electron transport between PSII and photosystem I (PSI), measured in µs

Methods:

Treatments were prepared using sterile seawater enriched with f/2 nutrients. 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 1 L glass bottles and staged in a climate-controlled chamber kept at 19° C. All treatments were grown in triplicate with true biological replication. Every day, samples for EOE (5 mL), chlorophyll, and photophysiology (4 mL) were retrieved from every experimental bottle. To each of the EOE samples, 15 mL of dichloromethane was added, and samples were transferred to a fridge until analysis using a spectrophotofluorometer. The samples for chlorophyll and photophysiology were left to dark-acclimate for ~10 minutes before being transferred into a FIRe (Fluorescence Induction and Relaxation) system (Satlantic, Halifax, Canada). Parameters were collected from both single turnover (ST) and multiple turnover (MT) curves, using 10 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).

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