Undergraduate Research

Studying tiny ocean organisms on a large scale: How do we make sure we have accurate, useful data?

Each summer, the University of Rhode Island Graduate School of Oceanography (GSO) hosts undergraduate students from all over the country to participate in oceanographic research. These Summer Undergraduate Research Fellows (SURFOs) have not only been working with GSO scientists, but they also have spent part of their time learning how to communicate this science to the public. Read on to find out what they have been up to, and why everyone should be as excited as they are about their work.

The author of this post, Amanda Herbst, is a rising senior at Cal Poly, San Luis Obispo where she is majoring in Chemistry and minoring in Dance. This summer she worked with Pierre Marrec and Susanne Menden-Deuer through the URI GSO Summer Undergraduate Research program.

 

No Plankton, No Life

Captured in this image is a variety of phytoplankton observed during an oceanographic survey in the North Atlantic this past July. Credit: Jason Schaedler, Menden-Deuer Lab

Phytoplankton are microscopic organisms that live in the upper part of the ocean. Just like plants on land, they take up carbon dioxide and use sunlight to produce their own food, through photosynthesis, and then release oxygen. Although most phytoplankton are smaller than the human eye can detect, all life on Earth is directly or indirectly reliant on them as they make up the base of oceanic food webs. This means that the majority of life in the ocean, from other plankton to fish to whales, rely on them for fuel. Their ecological significance makes phytoplankton a vital subject to study and understand, which is something I wasn’t fully aware of before this summer.

 

A Sea of Data

A woman (Amanda Herbst) in rain boots stands at in a lab aboard a ship with science equipment. She is filtering water samples.
Here I am filtering water samples for discrete data on board the R/V Endeavor.

All types of phytoplankton use a green pigment called chlorophyll-a to photosynthesize. By measuring the amount of chlorophyll-a in a given amount of water, we can estimate the amount of plankton within. The higher the concentration of chlorophyll-a in the water, the more phytoplankton. 

Just like how your white shirt glows under a black light, chlorophyll-a has a special property where it will fluoresce, or emit a certain wavelength of light that we can detect, when excited by a different wavelength. We can measure this fluorescence and convert the value into a concentration of the pigment. There are a couple different ways to obtain these measurements–one provides discrete data, the other continuous data.

Discrete data are obtained from individual water samples that are put through a filtration and extraction process before measurement. This gives us accurate and precise results, but is time-consuming and costly. We can alternatively collect continuous data by measuring chlorophyll-a fluorescence directly in the water as it passes through an instrument. This type of measurement allows us to easily collect thousands of data points and is extremely useful when trying to understand phytoplankton distribution across large spaces and times. However, the continuous data is often not as accurate, so it needs to be calibrated with the discrete data in order to be reliable.

 

Cruising for Plankton

Example of the continuous fluorescence data collected across the Northeast U.S. Shelf during the summer of 2019. Credit: Amanda Herbst

The Northeast U.S. Shelf Long-Term Ecological Research project began in 2018 and studies an ecologically and economically important ecosystem in the Atlantic Ocean (see map to the right). The near-shore waters are home to a rich marine ecosystem that we depend on. Here, there are large commercial fishery operations, activities to enjoy such as sailing, kayaking, and other water sports, and conservation efforts including protecting the vulnerable Atlantic salmon. The main goal of the project is to understand the link between the environment and planktonic food webs. Every winter and summer, the research vessel, the R/V Endeavor, travels across the Northeast U.S. shelf on a 6-day cruise while collecting physical data such as temperature and salinity, as well as biological data including chlorophyll-a fluorescence. The ship has a system that pumps ocean water through scientific instruments onboard, which take chlorophyll-a measurements every minute. This continuous data gives us a good understanding of the distribution of phytoplankton in the surface of the water along the ship’s path. But, as mentioned above, the data needs to be calibrated. Therefore, throughout the cruise, additional discrete water samples are taken directly from the system and measured for chlorophyll-a concentration. 

Here, I am helping to lower a CTD (conductivity, temperature, and density) rosette into the ocean to collect water samples at different depths in the water column. Credit: Jason Schaedler, Menden-Deuer Lab

And this is where I come in. This summer, I used the discrete data samples to calibrate the less accurate continuous data for six cruises, including the one this summer, which I had the opportunity to go on. As it was my first research cruise, I was both nervous and excited (and a little worried about getting seasick), but I learned so much and witnessed some fascinating science in action. I was even able to collect my own samples that I then used in my project once I was back on land. 

By calibrating the continuous data, I am making it accurate and useful. And even better, it will be published to an environmental data repository for others to use for future research. This might include validating chlorophyll-a data obtained from models and satellites, as well as helping to further the study of how phytoplankton distribution–and the organisms that depend on them, including the lobster and cod on our plates–may change in the future. Overall, I have enjoyed contributing to advancing data accuracy and accessibility in a big way, even if the phytoplankton themselves are very tiny.   

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