Abstract: Zooplankton is an immensely numerous and diverse group of organisms occupying every corner of the oceans, seas and freshwater bodies on the planet. They form a crucial link between autotrophic phytoplankton and higher trophic levels such as crustaceans, molluscs, sh, and marine mammals. Changing environmental conditions such as water temperatures, salinities and pH values currently create monumental challenges to their well-being. A signi cant subgroup of zooplankton are crustaceans of sizes between 1 and 10 mm. Despite their small size they have extremely acute senses that allow them to navigate their surroundings, escape predators, nd food and mate. In a series of joint works with Rudi Strickler (Department of Biological Sciences, University of Wisconsin - Milwaukee) we have investigated various behaviors of crustacean zooplankton. These include the visualization of the feeding current of the calanoid copepod Leptodiaptomus sicilis, the introduction of the \ecological temperature" as a descriptor of the swimming behavior of water eas Daphnia pulicaria and the communication by sex pheromones in copepods. The tools required for the studies stem from optics, ecology, neuroanatomy, computational uid dynamics, and computational neuroscience.