When we think of predators, pumas, hawks, and killer whales may come to mind. But, predators exist on the single-cell scale as well. Here’s a picture of a single-celled predator called a tintinid, who’s trying to eat a large algal cell, the spikey diatom corethron.
One mission on the cruise is to identify who’s eating whom in this Antarctic food web. We’re looking directly at what the krill are eating, but we can also try to capture the feeding of even tinier predators. Single-celled organisms that can be seen through a microscope are predators to one another, and to the algae in the water. These tiny predators are known as zooplankton. Using these bottles, incubated in seawater constantly flowing through large on-deck tanks, we measure the grazing of single-celled predators on the marine algae. Basically, we’re testing whether or not the zooplankton are eating their veggies!
We capture the signal of zooplankton grazing by incubating water over 24 hours, and measuring the growth of algae with and without grazers present.
Grazing experiments are conducted in these large tanks, which maintain the temperature of the seawater (cold! around -1.9 degrees Celsius!). The sewater is constantly flowing through the tanks to maintain temperature, and prevent ice from forming.