Brine shrimp (Artemia franciscana) leave feeding tracks in the surface film (neuston) as they graze along the surface of a microcosm experiment. The experiment was designed to test mercury uptake by brine shrimp in the Great Salt Lake, but it yielded interesting information on swimming and behavior as well. The nature of the surface film is unknown, and the shrimp did not seem to be removing it.
"Neuston" is the term for organisms that live on top of, in, or clinging to the surface film of water.