Research Experiences for Undergraduates (REU) Student Chris Payne Presents DROPPS Research

Every summer, the University of Texas Marine Science Institute (UTMSI) admits Research Experiences for Undergraduates (REU) interns to participate in exciting research, giving them valuable experience that will prepare them for careers in marine science. After choosing a research topic and mentors, they spend the summer working on their projects and give a final presentation at the REU Symposium at the end of the summer. 

Chris Payne, a marine biology major from Boston University, is one such student. He decided to work with DROPPS because he realized the value of studying oil spills and wanted to help be a part of the solution to this complicated problem.

There have been many studies on how oil affects macrofauna, but not as many studies on the impacts it has to the base of the marine food chain: plankton.  These tiny organisms are important for many reasons. Plankton are important contributors to primary and secondary production. Also, toxic species can cause harmful algal blooms when they are in large numbers. They also form important links in the marine food web, and finally, they provide organic matter to deep sea ecosystems through marine snow.

Research Questions

Chris Payne presents at the REUfest
2015 Summer Symposium
Credit: Lalitha Asirvadam

Chris’ research focused on these questions: What effect does oil and dispersant have on natural plankton populations? How do changes in oil and dispersant concentrations affect natural plankton communities? Chris worked closely with his mentors, Dr. Brad Gemmell and Dr. Ed Buskey from DROPPS, to try and find answers to these questions.

Background

In preliminary experiments, Dr. Gemmell has looked at the dinoflagellate Prorocentrum and its ciliate grazers. He exposed them to oil and dispersants and observed changes in populations. His results indicated that dispersants inhibit ciliate growth which led to population increases in dinoflagellates. Chris wondered if similar results can be seen in natural plankton populations.

Methods

His study consisted of three experiments: two using nearshore water and one using offshore water. The water was filtered to remove large zooplankton. Each experiment used three treatments: filtered sea water, seawater with crude oil, and seawater with crude oil and dispersant. Both offshore and nearshore experiments were exposed to 20 µL Lˉ̄ ¹ of crude oil, while an additional treatment was conducted for nearshore water with 50 µL Lˉ̄ ¹ concentration of oil. A 20:1 ratio of crude oil to dispersant was used in all three experiments. For the nearshore experiments, 10 mL samples were taken daily and Chris counted diatoms, dinoflagellates, and ciliates using microscopy, FlowCAM, and flow cytometry. The offshore samples had to be settled in 50 mL settling chambers and were counted using microscopy.

Results

For the 20 µL Lˉ̄ ¹ crude oil nearshore experiment, Chris found no significant differences among the total populations of the control, oil, and oil plus dispersant treatments. The 50 µL Lˉ̄ ¹ nearshore experiment, however, showed significant differences among the total populations of each treatment.

Conclusion

In summary, Chris observed that oil and dispersants have a negative effect on diatoms; however, dinoflagellates appear to be resistant to the toxicity of oil and dispersants. In addition, higher concentrations of oil have a more significant impact on plankton populations while offshore populations were more affected by 20 µL Lˉ̄ ¹ concentration of crude oil than the nearshore populations.  And finally, a population of small (approximately 2 micron) organisms becomes much more abundant in oil and oil + dispersant treatments. It may be that small nanoplankton (such as Synechococcus) are resistant to oil and dispersant.

Chris gave his final presentation on August 5, 2015. He said that he learned a lot and enjoyed his time as an REU student at UTMSI. He is currently thinking about a future in marine conservation.

Research sponsored by the Gulf of Mexico Research Initiative 

Oil and Plankton: DROPPS Takes a Closer Look Using Laser Technology

The interactions of plankton with oil droplets is a fascinating but relatively unexplored area. Scientists in the DROPPS Consortium previously looked at oil droplets rising though thin layer of plankton to see how they interact with oil. This time DROPPS wanted to look further into what may have happened in the dispersed oil layers between the well head, at approximately 5000 feet below sea level, and the ocean surface. DROPPS Scientists used holography technology, small scale experiments in the lab, and a recently constructed tower tank, measuring approximately 4 meters tall, for their latest experiments.

During the week of June 22^nd 2015, DROPPS scientists Ed Buskey, Brad Gemmell, Jian Sheng, Joe Katz, David Murphy, Cheng Li, Larry David, Vincent d'Albignac and Jeffrey Cordero convened at the University of Texas Marine Science Institute (UTMSI) in Port Aransas, Texas to participate in the experiments.

DROPPS’ recent experiments involved holography technology which allows you to construct volume in 3D. This shows a 3D distribution of water and how it interacts with particles. DROPPS scientists were able to take a closer look at what could have happened to plumes of oil released from the Deepwater Horizon well head that had been mixed with dispersant. Studies showed dispersants created subsurface plumes of tiny oil droplets.  DROPPS recreated this in the laboratory by creating a layer of microscopic droplets (by adding dispersant to oil and mixing it up with seawater using stir plates), mimicking the subsurface layers associated with the Deepwater Horizon. They also created varying density layers in the water (by slightly changing the salinity), with the most dense water at the bottom, intermediate water in the middle, and lighter water at the top. They wanted to see how quickly oil would diffuse through these layers. Seawater density can change throughout the water column, with the most rapid changes often occurring near the bottom of the thermocline.  With the tower tank experiments, they set up layers to see how the micro oil droplets would disperse naturally, with and without small organisms swimming through it or with larger organisms stirring up the water.  This would help measure the importance of biogenic mixing (mixing of the ocean by animals), an idea that has recently been of great interest to biologists and oceanographers.

Small scale experiment in lab. Photo by Jeffery Cordero

First, DROPPS scientists conducted small scale experiments in the lab. In these experiments, they added small zooplankton, copepods mostly, and used PIV to examine how or if they mixed a layer of oil. The copepods did not seem to have much effect on the dispersion of the oil layer, probably because they were too small.  Tiny oil droplets have natural fluorescence so they glow when exposed to certain wavelengths of light. This allows DROPPS scientists to measure how well the animals mix the oil-water emulsion layer in comparison to natural diffusion.

A ctenophore suspended in water. Photo by Jeffery Cordero

 In the large tower tank experiment, they produced physical dispersion by using larger organisms (jellyfish), which had more of an effect on the layer containing dispersed oil.

Tower Tank. Photo by Jeffery Cordero

 In the future they hope to use intermediate sized organisms such as shrimp and small fish to examine their effects of biogenic mixing of dispersed oil. In the future, DROPPS scientists also wanted to study how these organisms interact with the dispersed oil layers; do copepods and other small zooplankton feed on the oil? Does this make them more susceptible to their predators (jellyfish and small fish)?

Video by Jeffery Cordero

Research sponsored by the Gulf of Mexico Research Initiative