The vertical migration of zooplankton in relation to predator avoidance.

Abstract

This project examines vertical migration of zooplankton in relation to predator avoidance. There are several hypotheses as to why zooplankton may exhibit this migratory pattern. Our hypothesis is that fish are visual predators and zooplankton migrate to avoid predation. We predict that the number of zooplankton at higher depths will increase during the night and decrease during the day. We measured the number of zooplankton at four varying groups according to size and species. Light intensity was measured during the day for each of the four days samples were collected. We concluded that vertical migration was not occurring among the two different types of zooplankton or sizes classes. The zooplankton were then exposed to predators under controlled conditions. Three tanks were exposed to twelve hours of light, the other three to twelve hours of darkness. After 24 hours, a known amount of zooplankton was added to each sample. After twelve hours the number of zooplankton remaining in each tank was calculated which, when compared to the sample already counted, gave the amount of zooplankton which had been eaten by the fish. We found a significant difference between the size of the species, the species themselves, and the night and day simulations.