The Small Stuff Matters

The most important form of life in the ocean also happens to be the smallest. Phytoplankton provide the foundation of marine food webs, regulating global climate and the transport of nutrients and carbon. Phytoplankton populations fluctuate, sometimes growing high in numbers if they receive plenty of sunlight or nutrients. Other times, phytoplankton experience mortality, mainly from hungry grazers called microzooplankton (slightly larger carnivorous plankton) or from infectious viruses. As such vital components of the marine ecosystem, it is important to understand the balance between phytoplankton growth and death.

This is where we come in – our research team, which includes oceanographers from URI and UGA, are working to measure how often phytoplankton grow or die in the North Atlantic Ocean. Ultimately, we hope to link these findings of phytoplankton dynamics to larger-scale ocean and atmospheric measurements being made on the cruise.

On the cruise, we perform 24-hour incubation experiments with seawater collected from the water column. We sample the seawater the day its collected and a day later, measuring changes in the phytoplankton community using a range of instruments on board. One such instrument, the flow cytometer, allows us to count microscopic phytoplankton cells one-by-one. The flow cytometer takes up a sample and uses a laser to shine each cell as it passes by, distinguishing them based on specific size and fluorescence properties. After running a sample, we circle the populations, add some color to easily distinguish them and count the number of cells within each population. By comparing the number of cells gained or lost in a population each day, we can directly measure their growth and mortality rates!

Flow cytometry is just one technique we are employing on this cruise, but it is already helping to advance our knowledge of phytoplankton in the North Atlantic.

Written by Sean Anderson

Tags: NAAMES-III 2017