Artemia are passive filter feeders that forage by ingesting large amounts of water that contain phytoplankton. The nutritional value of food for brine shrimp is measured by "assimilation rate and efficiency", or how fast a shrimp is able to take up food and how efficiently it uses those nutrients to grow. Another measured aspect of this process is respiration rates, because the more a shrimp has to move around to find food, the more energy it needs.
Laboratory tests have shown that growth rates of Artemia fluctuate depending on the variety of phytoplankton they feed on. Algae with high protein and lipid reserves resulted in high growth rates. These were Chlamydomonas sphagnicolo, Dunaliella viridis, and Platymonas elliptica. An alga, Nitzchia closterium, with low protein and lipid levels but a high amount of carbohydrate resulted in slow growth when fed to Artemia.
Brine shrimp in the Great Salt Lake are not able to select high quality phytoplankton, nor are they able to adjust their metabolism based on food availability. This is likely tied to cyst production; because an adult is able to ensure that their genes will be passed on to the next generation regardless of present habitat conditions, there was little pressure to develop selective and active feeding mechanisms. The survival of adult brine shrimp is completely dependent upon food quality and quantity, while offspring are protected until food quality and quantity are such so that they can survive.