Food consists of dinoflagellates and other small forms.
"Marine Protozoa from Woods Hole" by Gary N. Calkins
Diagram of transverse fission of a Dinoflagellate.
"Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 5" by Various
Tropical coral reefs live in a close relationship with single-celled algae called dinoflagellates.
In addition to its symbiosis with the coral, the cyanobacteria also may have a relationship with the dinoflagellates, the latter supplying the bacteria with glycerol, for example.
The tiny marine dinoflagellate Karenia brevis produces brevetoxin, which in high concentrations is responsible for the harmful algal blooms known as red tides that occur in the waters off the west coast of Florida.