Zooplankton are microscopic invertebrate animals that swim or drift in water. They are at the base of the food chain, feeding on microscopic plants and being fed upon by aquatic insects, fish and salamanders. Their sizes usually range from one-tenth of a millimeter to four millimeters, which is smaller than the head of a pin. Most zooplankton are filter feeders, using their appendages to strain bacteria and algae and other fine particles in the water. Because the animals are wholly aquatic but often live in habitats that dry temporarily, they are faced with problems related to the unpredictability of their watery existence. Different types of zooplankton respond to these challenges in various ways. Adult females may lay different types of eggs, depending on the season and whether the pond is likely to dry soon. Other zooplankton are tiny crustaceans, like Daphnia. (If you include krill and copepods, which can swim, this group constitutes about 70 percent of all plankton)
Like land plants, phytoplankton have chlorophyll to capture sunlight, and they use photosynthesis to turn it into chemical energy. They consume carbon dioxide, and release oxygen. All phytoplankton photosynthesize, but some get additional energy by consuming other organisms. Phytoplankton growth depends on the availability of carbon dioxide, sunlight, and nutrients. Phytoplankton, like land plants, require nutrients such as nitrate, phosphate, silicate, and calcium at various levels depending on the species.
Lasenby, D.C., M. Furst. 1981
Mysis is a truly omnivorous filter feeder. Algae, detritus, and other zooplankton are all consumed. Diet may vary from lake to lake, season to season, and year to year depending on availability of food items and abiotic factors. Deep, cold waters with high levels of dissolved oxygen are preferred by Mysis relicta. The species tends to inhabit deep oligotrophic lakes that provide ample oxygen and suitable temperatures during the heat of summer when stratified eutrophic lakes experience oxygen depletion in the hypolimnion. Adult lake trout and whitefish prey heavily on Mysis due to the fact that they feed near the bottom during the daytime in the deep waters. Rainbow trout are feeding on the Mysis at night when the temperatures cool. (We have seen this in the stomach content of Rainbows in Grand lake)