Zooplankton in Sanya Bay, China move up and down in the water at different times of day. In spring, they stay near the surface, but in summer, they sink during the day and rise at night. Some species move in different ways, like sinking during the day and rising at night, or rising at dusk and dawn. Light affects their movement, but not the amount of phytoplankton in the water. In summer, some larger zooplankton can even reach the surface. The way zooplankton move up and down is linked to their size, the depth of the water, and their natural behavior.