<P> Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes . The migration occurs when organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone of lakes during the day . The word diel comes from the Latin dies day, and means a 24 - hour period . It is the greatest migration in the world in terms of biomass . This form of migration is not restricted to any one taxa as examples are known from crustaceans (copepods), molluscs (squid), and ray - finned fishes (trout). There are various stimuli responsible for this phenomenon, the most prominent being response to changes in light intensity, though evidence suggests that biological clock s are an underlying stimulus as well . There are a number of potential reasons to explain the phenomenon in nature, though it is most typically to access food and avoid predators . While this mass migration is typically nocturnal, with the animals ascending from the depths at nightfall and descending at sunrise, novel types of vertical migration can occur in response to the different cues and stimuli that trigger migration . Some novel events include the absence of DVM during midnight sun in Arctic regions and the sudden onset of migration due to a solar eclipse . </P> <P> During World War II the U.S. Navy was taking sonar readings of the ocean when they discovered the deep scattering layer (DSL). While performing sound propagation experiments the University of California's Division of War Research (UCDWR), consistently had results of the echo - sounder that showed a distinct reverberation that they attributed to mid-water layer scattering agents, there was speculation these readings may be attributed to enemy submarines . By collaborating with biologists from Scripps Institution and the UCDWR, they were able to confirm that the observed reverberations from the echo - sounder were in fact related to the diel vertical migration of marine animals . The DSL was caused by large, dense groupings of organisms, like zooplankton, that scattered the sonar to create a false or second bottom . </P>

What is an advantage of daily vertical migration by marine zooplankton quizlet