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Swimming Behavior of the Florida Red Tide

Red tide organisms are a type of plankton, which means they float with the currents in the ocean. Some plankton are able to swim very short distances. The Florida red tide organism, Karenia brevis, is one of these motile organisms.  It has two flagella, or whiplike structures, that propel and direct it through the water. One flagellum twists and turns the cell while the other propels the cell through its environment. Karenia brevis can swim at a speed of up to 3 feet per hour – not very fast!

Many of our research questions about K. brevis focus on its ability to form dense blooms.  How can this single organism dominate an entire community of diverse algae and reach such high concentrations?  Does it have an advantage over other algae? Scientists believe that the daily migratory behavior of K. brevis may be one factor that gives it an edge over other algae in the ocean. We know that many dinoflagellates swim to deeper, darker waters to take up dissolved nutrients at night. Then, during the day, they swim to shallower, sunlit waters to photosynthesize.  Such daily migration may allow K. brevis to find optimal light and nutrient regimes when other non-motile algae cannot.

Scientists at FWRI are studying how changes in the physics and chemistry of the water column may affect the migratory behavior of K. brevis.  One hypothesis is that cells will be able to more freely migrate in well-mixed environments where salinity and temperature are uniform.  In contrast, in an environment with a sharp salinity or temperature change, the cells might not cross over to the new environment.  This layering of water would serve as a barrier that restricts migration and affect nutrient or light access and K. brevis distribution.  

Researcher Matt Garrett has designed experiments (as part of his thesis research) to address the following questions:

  • What is the natural migratory behavior of K. brevis in uniform environments?  That is, how does it migrate throughout a daily cycle?

  • How does the presence of weak and strong temperature boundary affect migratory behavior? How does the presence of nutrients such as nitrogen in one layer affect migratory behavior?

Experiments are conducted in a simulated water column - a 6-foot tall PVC cylinder which we keep in a temperature- and light-controlled incubator. First, researchers set up different physical conditions by creating temperature barriers. They wrap tubing filled with chilled water around the lower half of the column to keep the lower column cool and the upper part of the column warm. The column is filled with a culture of K. brevis and scientists track its movement for 48 hours. So they do not disturb the water column once it is set up, researchers track movement with instruments called fluorometers that are attached to the column at different depths.  They can also sample cells by removing them through ports in the column. The results so far have shown that the presence of a weak temperature gradient (1.5 °C difference between the surface and bottom) delays the migration to depth at night, and a strong temperature gradient (3.7 °C difference) stops the movement all together. Future experiments will explore how K. brevis behavior might change when nutrients are added to one of the layers. Will migration be quicker? This work will allow us to better understand K.brevis behavior and the formation of blooms.  Scientists can use the results from their experiments in the lab to predict the conditions under which K. brevis may bloom in nature.