Abstract:

Ocean acidification (OA) and its effects on seawater carbonate chemistry affect all marine organisms, especially those that utilize inorganic carbon for photosynthesis. The effects of oil compounds on phytoplankton in future OA conditions has not been well studied. Roller table experiments with Thalassiosira pseudonana, a small centric diatom, were conducted to produce marine snow aggregates in six treatments: Control (pCO2 = 400 ppm), OA (pCO2 = 750 ppm), water accommodated fraction of oil (WAF), OAWAF, diluted chemically enhanced WAF (DCEWAF), and OADCEWAF. Measurements included intracellular photophysiological responses, oil concentrations and polycyclic aromatic hydrocarbons (PAHs), aggregate morphology, transparent exopolymeric particles (TEP), and extracellular polymeric substances (EPS) to investigate if OA will affect the response to oil spill conditions. The experiments were conducted in the dark to eliminate cell replication and photosynthesis and used both stationary and exponential growth phases.

Suggested Citation:

Jennifer Genzer, Jessica Hillhouse, Manoj Kamalanathan, Laura Bretherton, Antonietta Quigg. 2020. Potential impacts of ocean acidification on diatom aggregation when exposed to crude oil and chemical dispersants. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/VF86SWMX

Publications:

Genzer, J. L., Kamalanathan, M., Bretherton, L., Hillhouse, J., Xu, C., Santschi, P. H., & Quigg, A. (2020). Diatom aggregation when exposed to crude oil and chemical dispersant: Potential impacts of ocean acidification. PLOS ONE, 15(7), e0235473. doi:10.1371/journal.pone.0235473

Purpose:

To investigate how an oil spill may affect diatom aggregation in future ocean conditions.

Data Parameters and Units:

Dataset consists of 1 Excel file which contains several experimental treatments examined under the stationary and exponential phases. The treatments are as follows- Control (no additions), OA ocean acidification (adjusted carbonate chemistry), WAF (water accommodated fraction of oil), OAWAF, DCEWAF (dilute chemically enhanced water accommodated fraction of oil), and OADCEWAF. Main parameters: FvD/FmD: relative fluorescence Sigma PSII: Å2 (quanta)-1 Ρ: ρ Chlorophyll a: microgram Cell counts: cells per mL Aggregate area: cm2 Aggregate counts Aggregate mean gray-value Aggregate aspect ratio Aggregate settling time: seconds Neutral sugars: mg Uronic acids: mg Proteins: mg Transparent exopolymeric substances: Polycyclic aromatic hydrocarbons: mg or ng g-1 Equivalent spherical diameter: mm Estimate oil equivalent: mg L-1 pH pCO2: ppm TCO2: µmol kg SW-1 HCO3-: µmol kg SW-1 CO32-: µmol kg SW-1 CO2: µmol kg SW-1 The two worksheets split between stationary and growth phase experiments. Data divided between the initial time point (t=0) and final time point (t=f). No measurements were taken between the beginning and end due to the nature of the experimental design.

Methods:

WAF was prepared in darkness over 24 hrs in a 120L continuous flow-through baffled recirculating tank system (Wade et al. 2017) using 0.4 mL Macondo surrogate oil per L artificial seawater. For DCEWAF, the oil was premixed with Corexit (ratio of 1:20). This mixture was added (0.4 mL per L artificial seawater) to 9 L aspirator bottles, as smaller volumes were required, and left to mix with a stir bar and plate over 24 hrs in total darkness. Methods of extraction of PAH from water: Samples were frozen at -20ºC prior to PAH extraction. Each sample was thawed and spiked with 50 μL of internal standards (d8-naphthalene, d10-acenaphthene, d10-phenanthrene, d12-chrysene and d12-perylene). SSW samples (700 mL) were extracted with dichloromethane as described in Morales-McDevitt et al., (2019). Following the dichloromethane extraction for AGG samples (5 mL), the samples were gravity filtered through a glass Monstr-Pipette containing silica gel/sodium sulfate to remove the organic particulates (Morales-McDevitt et al., 2019; Shi et al. 2019).

Instruments:

FIRe: Satlantic Fluorescence induction and Relaxation fluorometer system EOE: RF-5301 PC Spectrofluorophotometer Billy: 10AU Turner Designs fluorometer Microscope: Olympus CH2 pH probe: Fisher scientific Accumet AB15 pH probe TEP: Genesys 10S UV-Vis spectrophotometer GERG GC/MS: Agilent 6890N GC system with 5975CMSD EPS: Beckman Coulter Allegra x-12 Centrifuge Biotech Epoch plate reader

Provenance and Historical References:

Wade, T. L., Morales-McDevitt, M., Bera, G., Shi, D., Sweet, S., Wang, B., Gold-Bouchot, G., Quigg., A. & Knap, A. H. (2017). A method for the production of large volumes of WAF and CEWAF for dosing mesocosms to understand marine oil snow formation. Heliyon, 3(10), e00419. doi:10.1016/j.heliyon.2017.e00419 Morales-McDevitt, M. E., Shi, D., Knap, A. H., Quigg, A., Sweet, S. T., Sericano, J. L., & Wade, T. L. (2020). Mesocosm experiments to better understand hydrocarbon half-lives for oil and oil dispersant mixtures. PLOS ONE, 15(1), e0228554. doi:10.1371/journal.pone.0228554 Shi, D., Bera, G., Knap, A. H., Quigg, A., Al Atwah, I., Gold-Bouchot, G., & Wade, T. L. (2020). A mesocosm experiment to determine half-lives of individual hydrocarbons in simulated oil spill scenarios with and without the dispersant, Corexit. Marine Pollution Bulletin, 151, 110804. doi:10.1016/j.marpolbul.2019.110804

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