Mysis relicta in Lake Michigan: abundances and relationships with their potential prey, Daphnia

Diel vertical migration produced maximum concentrations in the thermocline at night of 1-10 mysids.m^-3. Variation among replicates averaged 28% with a 3-net Tucker trawl and 19% with Puget Sound vertical closing nets. Mean areal abundances over 5 yr averaged 110 mysids.m^-2 (range 25-645). Synoptic cruises from 43°N to 45°N during August indicated that densities were considerably greater offshore than inshore, and greater in the N than in the S. Although Mysis is potentially an important predator on Daphnia, differences in nighttime vertical distributions reduce encounters between Mysis and Daphnia during summer in Lake Michigan, such that Mysis exert mortality rates on Daphnia of <1.5% per day; the latter are in general <10% of the birth rates of Daphnia populations. -from Authors