By Alexis Oetterer
Amid the pandemic this summer, the REU has been about staying flexible and going with the flow. Flow cytometry, that is. For my research project, I am working with Dr. Nicole Poulton to analyze the predator-prey dynamics of Mesodinium spp. and Dinophysis spp. in the Boothbay region of the Gulf of Maine.
To do this, flow cytometry is a powerful tool to quickly quantify and evaluate cells collected in water samples. It was originally used in medicine to count blood and cancer cells, and Bigelow scientists were the first to apply it to ocean research. Water samples, which have been collected from various sites weekly to biweekly as part of an ongoing time series, are entered into a flow chamber. A pump downstream draws the sample through the instrument, forcing the cells through in single file. They pass in front of a laser beam and based on the characteristics of the cell, the light is scattered.
The angle at which it scatters depends on the size, shape, and refractive index of the cell. Depending on the pigments of the particle, it will emit fluorescence at different wavelengths (for instance, chlorophyll fluoresces red and phycoerythrin fluoresces orange). The signals from the fluorescence and light scatter are processed by the computer and used to create a scatterplot. From this data, total populations of organisms can be determined; however, it is imagining-in-flow analysis (FlowCAM) that allows for the enumeration of specific taxonomic groups. The FlowCAM flash illuminates the sample and a camera is triggered at short intervals. The images of the particles are used to generate an image library, which can then be reviewed to examine morphology of cells and visually classify organisms and particle types. I will compare population abundance data from 2016, 2017, and 2018 to analyze changes in populations and to see if there are any correlations with biophysical parameters.
The key players in this dynamic are cryptophytes, Mesodinium, and Dinophysis. Cryptophytes are a type of autotrophic nanoplankton that contain chloroplasts. Mesodinium, a type of ciliate, ingests cryptophytes and sequesters their chloroplasts, leading to increased growth and photosynthetic rates. After stealing plastids from cryptophytes, Mesodinium subsequently gets robbed by Dinophysis, a type of dinoflagellate. Dinophysis can maintain the plastids for several generations which allows them to grow even when prey is absent. This entire dynamic occurs microscopically, but it illuminates the fact that predator-prey interactions and food webs are not as direct or conventional as some might think.
The dynamic is important to study because the Gulf of Maine has warmed faster than 99% of the global ocean over the course of a decade. With shifts in ocean conditions, the dynamics of phytoplankton are also likely to change. Dinophysis is a species of concern, since it forms toxic algal blooms which could harm the shellfish industry. As climate change intensifies, blooms are becoming more frequent and occurring in new locations. The availability of Mesodinium is necessary for a bloom, prompting us to ask questions about whether or not we see similar dynamics between collection sites, if the presence of Mesodinium can be used as a leading indicator of a Dinophysis bloom, when peak blooms occurred in comparison to previous years, and how environmental factors affect bloom formation.
Although we all wish we could be together at Bigelow this summer, this experience has still been an incredible opportunity to meet people from across the country, converse with scientists passionate about their work, conduct research, and expand on the idea that science doesn’t follow a linear path: the career we plan on having might change, experimental methods have to be reworked, data doesn’t turn out as predicted, new programs and code have to be learned, rigorous statistical analysis needs to be conducted, etc. Where the next step leads can be a surprise, but it is a step I will always be willing to take.
Alexis Oetterer is a Truman State University student in Bigelow Laboratory for Ocean Science’s Research Experience for Undergraduates program. This intensive experience provides an immersion in ocean research with an emphasis on state-of-the-art methods and technologies.