Many of these animals can and do capture phytoplankton directly, and the ones that cannot, such as the fishes still take advantage of the nutritional quality of these tiny algae by preying on small animals that do eat them (such as copepods, rotifers and mysids).
Like with sea monkeys, you need to do everything exactly right to experience the full effect of your microscopic pets. According to the product listing, during the day, the plankton need to be placed in indirect natural light to photosynthesize. They'll glow in the dark when agitated (it's a defense mechanism, but you're not going to hurt your little friends.)
The plankton have a lifespan of a few months, but if you feed them nutrients and keep them in consistent temperatures they'll apparently reproduce indefinitely. You can buy more dinofood at the same link(Opens in a new tab) you used to purchase your aquarium. 781b155fdc