Opossum Shrimp (Mysis relicta) Predation on Zooplankton

Abstract

Mysis relicta clearance rates were not affected by changes in prey and predator density in single-prey systems where Epischura nevadensis late instars were used as food. A comparison of the results obtained from single-, two-prey, and multiple-prey systems revealed that Mysis clearance rates of E. nevadensis late instars and Diaptomus tyrrelli males were significantly affected by the presence and abundance of alternative prey.When offered natural prey assemblages, the smallest Mysis preyed preferentially on the smallest available prey (Bosmina, Ceriodaphnia, Diaptomus nauplii) while larger Mysis showed an increased preference for larger prey (Epischura, Daphnia). In general, Mysis preferred Daphnia over copepods; Epischura, Ceriodaphnia, Bosmina, and cyclopoid copepods over Diaptomus copepodites and adults; and Diaptomus males over Diaptomus females. Total consumption rates increased with increasing predator size and starvation duration. Food selectivity patterns exhibited by Mysis were attributed to the mechanical efficiency with which the predators captured and handled food particles of different sizes, to the vigor of prey escape responses, and to predator–prey encounter frequencies.Key words: Mysis relicta, predation, zooplankton, feeding preferences, opossum shrimp