Abstract:

The Deepwater Horizon oil spill released 4.3 million barrels of crude oil into the Gulf of Mexico (GoM). In the coastal zone of the GoM, phytoplankton are known to be nitrogen limited for most of the year, including the post spill period. Little is known about the phytoplankton response to nutrient availability in the presence of oil. Previous studies show that the diatom Phaeodactylum tricornutum (Pt) is resilient in the presence of oil and it is hypothesized to be an effect of its protective silica frustule. The purpose of this study was to test if nitrate and silica limitation affect the response of Pt in the presence of oil. Diatom cultures were grown in four different f/2 media nutrient treatments for a year: replete, -Si, ¼ N, and combination -Si and ¼ N. Each culture was subsequently inoculated into a control and water accommodated fraction of oil (WAF) treatment for 4 days. Samples were taken daily to monitor photosynthetic efficiency using fluorescence induction and relaxation and PhytoPAM, changes in chlorophyll-a concentrations, concentration of oil in the growth medium, and intracellular and extracellular macromolecular composition. Results showed that photosynthetic efficiency and growth rates were more affected by nitrogen limitation than the presence of oil. Extracellular macromolecular composition showed higher carbohydrate to protein ratios in the nitrogen limited treatments as well. In addition, Pt showed morphological variability with cells linking together in “chains” when Si and N limited for prolonged periods. This study could help us better predict how the GoM phytoplankton may respond to any future oil spills when affected by nutrient stress.

Suggested Citation:

Hillhouse, Jessica, Manoj Kamalanathan, Talia Rodkey, Andrew Mondragon, Noah Claflin, and Antonietta Quigg. 2021. Effects of nutrient availability on the diatom Phaeodactylum tricornutum in the presence of oil. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/1TBZJDET

Purpose:

To understand how nitrogen and silica limitation affect resistant diatom species, Phaeodactylum tricornutum, in the presence of oil.

Data Parameters and Units:

The dataset consists of 4 folders -Pt (-n) -fall 2018; Pt (-si and -n combo only)- spring 2019; pt (-Si and -N) fall 2019; and Pt (-si) -summer 2018. The headers in the Excel files-Sample ID, Emission, Conc. (mg/L), Sample Volume, Dilution Factor, Final Concentration (mg/L), Alpha(micromol e-.micromol-1 photons), ETRmax (micromol.electrons m2.s-1), Cell counts (cells per ml), Fv/Fm (relative fluorescence), Sigma PSII (Å2 (quanta)-1), Sigma PSII: Å2 (quanta)-1 Estimate oil equivalent (mg L-1), Neutral sugars (mg), Uronic acids (mg), Proteins (mg), FvD/FmD (relative fluorescence), blank, and Chl-a.

Methods:

WAF-Water accommodated fraction (WAF) of oil was made using Macondo surrogate oil added to f/2 media and stirred for 24 hours in the dark CEWAF-CEWAF was made by adding 400 µL of a 1:20 mixture (Corexit:oil) to each L of f/2 media and stirred for 24 hours in the dark DCEWAF-DCEWAF was made by diluting CEWAF 1:10 with f/2 media DDCEWAF-DDCEWAF was made by diluting CEWAF 1:20 with f/2 media Each treatment below was done in triplicate (A,B,C) C: Control treatment; f/2 media C (-Si): Control treatment without silica ;f/2 media without silica C (-N): Control treatment without nitrogen; f/2 media without nitrogen C (-both); Control treatment without silica and nitrogen; f/2 media without silica and nitrogen O: oil treatment; WAF made with f/2 O (-Si): WAF made with f/2 without silica O (-N): WAF made with f/2 without nitrogen O (both): WAF made with f/2 without silica and nitrogen M: CEWAF made with f/2 M (-Si): CEWAF made with f/2 without silica M (-N): CEWAF made with f/2 without nitrogen M (-both): CEWAF made with f/2 without silica and nitrogen DM: DCEWAF made with f/2 DM (-Si): DCEWAF made with f/2 without silica DM (-N): DCEWAF made with f/2 without nitrogen DM (-both): DCEWAF made with f/2 without silica and nitrogen DDM: DDCEWAF made with f/2 DDM (-Si): DDCEWAF made with f/2 without silica DDM (-N): DDCEWAF made with f/2 without nitrogen DDM (-both): DDCEWAF made with f/2 without silica and nitrogen

Instruments:

FIRe: Satlantic Fluorescence induction and Relaxation fluorometer system EOE: RF-5301 PC Spectrofluorophotometer Relative fluorescence: 10AU Turner Designs fluorometer WALZ Phytopam

Individual Files: